RADIO-FREQUENCY APPLICATION IN PREHEATING OF …

RADIO-FREQUENCY APPLICATION IN PREHEATING OF MARINATED

CHICKEN BREAST MEAT

by

DEEPTI DESHPANDE

(Under the Direction of Rakesh K. Singh)

ABSTRACT

Radio-frequency (RF) cooking is a form of dielectric heating in which products

are heated by subjecting them to an alternating electric field between two electrodes,

often parallel electrodes. In this study, the process of preheating marinated chicken breast

meat was optimized with a 6 kW radio-frequency oven. The denaturation temperatures of

chicken breast meat and its constituent proteins were determined by using a differential

Scanning Calorimeter. The samples were heated from 10 to 1000C at the heating rate of

100C/min. This thermal denaturation study further helped in designing a scheduled

heating sequence for cooking of chicken breast meat in an RF oven and resulted in the

most juicy cooked meat. RF preheating process was optimized by controlling various

parameters like the distance between electrodes, thickness of the product between two

parallel plate electrodes and the design of the product carrier. The best method for

presenting the product to the RF field was moving the product carrier through the

electrodes by the conveyor belt so that the product was exposed to the RF field while in

motion. This system ensures better heating uniformity of the product. A plastic material

transparent to RF waves made of polyetherimide, known as Ultem®, was procured and

used as product carrier. The cooked meat yields were determined as a function of

programmed preheating of marinated meat in the RF oven, followed by final cooking of

the product in a conventional air oven. Warner-Bratzler shear test were performed on

cooked samples to determine the quality of RF preheated product.

INDEX WORDS: Marinated Chicken Breast Meat, Radio-Frequency Heating,

Differential Scanning Calorimeter (DSC)


CHICKEN BREAST MEAT

by

DEEPTI DESHPANDE

B. TECH., LAXMINARAYAN INSITITUTE OF TECHNOLOGY, INDIA, 2005

A Thesis Submitted to the Graduate Faculty of The University of Georgia in Partial

Fulfillment of the Requirements for the Degree

MASTER OF SCIENCE

ATHENS, GEORGIA

2008

© 2008

Deepti Deshpande

All Rights Reserved


CHICKEN BREAST MEAT

by

DEEPTI DESHPANDE

Major Professor: Rakesh Singh

Committee: Romeo T. Toledo Stuart O. Nelson Karina G. Martino

Electronic Version Approved: Maureen Grasso Dean of the Graduate School The University of Georgia August 2008

iv

DEDICATION

I would like to dedicate this work to my friends and family for believing in me

and for their constant encouragement and support

v

ACKNOWLEDGEMENTS

I would like to thank Dr. Rakesh Singh and Dr. Romeo Toledo for giving me this

opportunity to work with them. It has been wonderful two years of experience under their

guidance and I have learnt so much. Thank you again for believing in me and being so

supportive throughout my research.

I would also like to thank Dr. Stuart Nelson for his assistance. He is a wonderful

professor. Many thanks to Dr. Karina Martino, for being on my committee. I am thankful

to Dr. Louise Wicker and Darlene for allowing me to work on meat proteins. I want to

thank Mrs. Mo Toledo. She has been my mom away from home and I really appreciate

her encouragement and support at every point.

This work could not have been possible without the help of Amudhan, Bilal and

Carl Ruiz. Thank you so much for helping me and working hard with me. I am also

thankful to the all the faculty and staff of food science department who helped me during

this project.

Thanks to my lovely friends, Preya, VJ, Tripti, Suavng, Lakshmi, PJ and so many

more I made during my stay here in Athens. They were so much fun to be with and I will

always cherish the wonderful times we spent together. Thanks to all my best friends

from school in India...you all helped me to become a better person in life.

vi

Last but not the least I want to thank my family …today what I am and what I

have achieved is because of you all. Especially I want to thank my Mom Mrs. Alka

Deshpande for always believing in me and who is my inspiration in life.

vii

TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS .................................................................................................v

LIST OF TABLES ........................................................................................................... viii

LIST OF FIGURES ........................................................................................................... ix

CHAPTER

1 INTRODUCTION .............................................................................................1

2 REVIEW OF LITERATURE ............................................................................3

3 RADIO-FREQUENCY APPLICATION IN PRE-HEATING OF

MARINATED CHICKEN BREAST MEAT ..............................................23

4 TRANSITION TEMPERATURES FOR CHICKEN BREAST MEAT AND

ITS CONSTITUENT PROTEINS ..............................................................62

5 CONCLUSIONS…………………………………………………………….93

viii

LIST OF TABLES

Page

Table 3.1: Percentage gain for four different treatments ...................................................51

Table 3.2: Percentage total moisture ..................................................................................52

Table 3.3: Effect of various treatments on purge, pH, expressible moisture and Cook yields……........................................................................................................53

Table 3.4: ANOVA for Design 1 .......................................................................................54

Table 3.5: Effect of Various Treatments on Gain, Cook Yields, Shear and Work of Shear…………………………………………………….……………….…..55

Table 3.6: ANOVA for Design 2……………………………….………………..............56 Table 3.7: Temperature distribution after final cooking in conventional air oven………57 Table 4.1: Absorbance readings for standard protein……………………………………80 Table 4.2: Absorbance Readings and Protein concentration for WSP and SSP…………81 Table 4.3: Summary of the Better Bradford Assay ……………………………………...82 Table 4.4: Protein concentrations diluted to 8 mg/ml for all samples to get constant

protein………..………………………………………………………………83 Table 4.5: Rf values and log MW for calibration curve of both gels …………………...84

Table 4.6: Molecular weights (MW) as estimated for the unknown WSP on gel 1……..85

Table 4.7: Molecular weights (MW) as estimated for the unknown SSP on gel 2 ……..86 Table 4.8: Peak denaturation temperatures for chicken breast meat and its constituent

proteins………………………………………………………………………87

ix

LIST OF FIGURES

Page

Figure 3.1: Dendrogram for Design 1 ................................................................................58

Figure 3.2: Dendrogram for Design 2 ................................................................................59

Figure 3.3: Time-Temperature data for Ultem® as product carrier ....................................60

Figure 3.4: Time-Temperature data for Rubbermaid as product carrier ............................61

Figure 4.1: Standard curve for meat proteins obtained by The Better Bradford Assay.....88

Figure 4.2: Calibration curve for Rf vs. Log MW for gel 1……………………………...89

Figure 4.3: Calibration curve for Rf vs. Log MW for gel 2 …………..............................90

Figure 4.4: Plot of Rf vs. Log MW for gel 2 ……………………………………………91

Figure 4.5: Transition peaks for marinated chicken breast meat ………………………..92

1

CHAPTER 1

INTRODUCTION

The safety of cooked meat and meat products is of increasing concern to

consumers, processors, and regulatory agencies. Conventional heating methods heat

foods starting from the exterior through conduction, convection or radiation and the

conduction of energy from the exterior to the middle of the solid food. The main

disadvantages of conventional heating methods are long cooking times, particularly with

thick solid pieces, and the existence of large temperature gradients between the surface

and the interior. The gradients result in overcooking the outside layers of the solid while

striving to reach temperatures in the slowest heating point in the solid lethal to pathogenic

microorganisms. Radio-frequency (RF) heating is a form of dielectric heating generated

when a material is positioned between two parallel plate electrodes and subjected to an

electric field with rapidly alternating polarity. Therefore, RF heating is potentially more

attractive than conventional heating methods, since heat is generated within the product,

thus eliminating the temperature gradient between the surface and interior of

conventionally heated whole-muscle meats. The focus of this research was to optimize

the process for preheating marinated chicken breast meat in an RF electric field. When

marinated meat is cooked, physical and chemical changes occur that changes the binding

of water in meat. Water held in the muscle is squeezed out during cooking when

collagenous membranes surrounding the muscle fibers and muscle fiber bundle contract

before the muscle protein gels.

2

Thus, a scheduled heating sequence in the cooking of meat would minimize the

release of water and will result in the most juicy cooked meat. The objectives of this

study were as follows:

(1) To determine the denaturation temperature profile of chicken breast meat using

Differential Scanning Calorimeter (DSC)

(2) To determine the efficiency of marinade pickup during RF heating

(3) To optimize the process parameters in order to preheat the marinated chicken

breast meat in RF oven

3

CHAPTER 2

REVIEW OF LITERATURE

Radio-frequency Cooking

Radio-frequency heating involves the transfer of electromagnetic energy directly

into a product, resulting in volumetric heating due to frictional interaction between

molecules. Although similar in some respects to microwave heating, RF heating has been

proposed to be more suitable for industrial heating of meats because greater penetration

depths are possible with this technology. The radio-frequency band of the

electromagnetic spectrum covers a broad range of high frequencies typically in the range

of 1 MHz to 300 MHz, while that of microwaves can be considered between 300 MHz

and 300 GHz (Ryynänen 1995). Both RF and microwave are considered non-ionizing

radiations as they do not have sufficient quantum energy to ionize compounds in

biological materials.

RF energy is generated by means of an RF generator that produces oscillating

fields of electromagnetic energy. The generator is comprised of an oscillator, power

supply and control circuitry. Heating of poor electrical conductors occurs when a high

voltage alternating electric field is applied to a medium sandwiched between two parallel

plate electrodes forming a capacitor configuration. The principle on which RF works is

such that, during heating, the product to be heated forms a dielectric between two metal

4

capacitor plates, which are alternately charged positively and negatively setting up a high

frequency alternating electric field. Three frequencies are commonly employed for RF

heating: 13.56, 27.12 and 40.68 MHz. Polar molecules such as water, try to align

themselves with the polarity of electric field. Since the polarity changes rapidly (at say 27

MHz, 27 million times/second), the molecules try to continuously realign themselves

within the electric field. Thus, the friction and kinetic energy caused by the colliding

neighboring molecules generates heat within the product, and the temperature of the

product rises (Piyasena and others 2003).

Advantages of RF heating include higher penetration depths, which are good for

large and thick products, and lower investment costs for RF equipment as compared to

microwave equipment. RF energy is also easier to understand and control as compared to

microwave energy. RF heating may be especially effective for large diameter foods like

meat because the low frequency of incident electromagnetic radiation allows greater

penetration depths (McKenna and others 2006). Risk of arcing is one of the major

disadvantages of using RF oven and there is not much data available on RF dielectric

properties as there is for microwave frequencies. Uneven temperature distributions are

also possible in RF cooked meat products as well as microwave heated products (Zhang

and others 2004b).

The microbial inactivation mechanisms of radio-frequency heating are quite

similar to those of microwave heating. Microwave and radio-frequency heating are

preferred for pasteurization and sterilization as compared to the conventional heating for

the primary reason that RF and microwave heating are rapid and therefore require less

5

time to reach the desired processes temperature. Microwave and RF heating may be

relatively uniform than conventional heating depending on the particular heating

situation. However, heating uniformity is difficult to predict. Other advantages of

microwave and RF heating systems are that they can be turned on or off instantly, and the

product can be pasteurized after being packaged.

Factors Influencing Radio-frequency Cooking

Dielectric properties

The dielectric properties of food are important factors that determine the

absorption and distribution of electromagnetic energy during dielectric heating. Dielectric

properties can be described in terms of complex relative permittivity εr:

rrr jεεε ′′−′= …………………………………………………………………………. (2.1)

where, 1−=j

The real part ( rε ′ ) of the relative complex permittivity is known as the dielectric

constant. The dielectric constant is a measure of the capability of a material to store

electrical energy. The imaginary part (rε ′′ ) of the relative complex permittivity is known

as the dielectric loss factor, which describes the ability of a material to dissipate energy in

response to an applied electric field (Wang and others 2003).

Materials with high values of dielectric loss factor will absorb energy at a faster

rate than materials with lower loss factors. The tangent of the dielectric loss angle (tan δ)

6

is called loss tangent or dissipation factor of the material. This is defined as the ratio of

dielectric loss factor (rε ′′ ) and dielectric constant (rε ′ ).

tan δ = r

r

εε

′′′ …………………..………………………………………………………. (2.2)

Factors affecting dielectric properties

The dielectric properties of foods are mainly dependent on temperature. The

effect of permittivity on temperature is represented by the following equation:

∆T / ∆t =

202 tanrf V

Cp

π ε ε δρ

′……………………………………………….....(2.3)

where ∆T = temperature increase (°C) in time t sec, f = frequency of dielectric

heating, ε0 = dielectric constant of vacuum, rε ′ = relative dielectric constant of material

to be heated, tan δ = tangent of dielectric loss angle, E = electric field strength (V/cm),

Cp = specific heat of material to be heated and ρ = density of the material to be heated.

The above equation shows that temperature increases with increasing loss factor.

However, if the loss factor is too high conduction current through the material negatively

affects the oscillator operation, and if it is too low, the heating rates are low. Hence to

achieve good heating rates the loss factor of the material should lie between 0.01<rε ′′ < 1

(Piyasena and others 2003).

E2

7

Penetration Depth

Another important factor affecting dielectric heating is penetration depth. It is

defined as the distance an incident electromagnetic wave can penetrate beneath the

surface of the material as the power decreases to 1/e of its level at the surface. It is

calculated by the following equation:

1/22

2 2 1 1rr

r

cdp

fεπ εε

= ′′ ′′ + − ′

………………………………………… (2.4)

where dp is the penetration depth, c is the speed of light in vacuum, 2.998×108

m/s, f is the frequency of dielectric heating, rε ′ = relative dielectric constant and rε ′′ =

dielectric loss factor of the material to be heated. This property is generally used to select

appropriate thickness of food package to ensure a relatively uniform heating along the

depth of a food package (Wang and others 2003).

In food materials, water and salt are the two major ingredients that influence

dielectric properties. Other food components usually have a minor influence on the

dielectric properties. It has been reported that physical changes such as fat melting and

protein denaturation affect dielectric properties. The dielectric properties are also

dependent on whether the electric field is oriented perpendicular or parallel to the fibrous

matrix of a food material (Bengtsson and others 1963). When starch gelatinizes, the

dielectric loss factor increases but there is no change in the dielectric constant (Miller and

others 1991).

8

The dielectric properties of many foods including meat and fish, agricultural

products, fruits and vegetables, bakery products, grains and dairy products have been

reported (Nelson and others 1994). The dielectric properties of food depend upon its

composition. Hence, it is helpful to conduct dielectric properties measurement for each

product that is to undergo a dielectric heating process.

Several studies have also been done to measure the effect of various factors like

temperature, moisture content, and ash content on dielectric properties of meat.

Sipahioglu and others (2003a) concluded that the dielectric constant of ham increased

with moisture and temperature and decreased with ash content. It was inferred that

increase in dielectric constant with temperature was a result of increasing levels of bound

water. Dielectric loss factor increased with temperature and ash content. Studies on

dielectric properties of turkey meat showed that as the water activity or ash increased, the

dielectric constant increased faster with temperature (Sipahioglu and others 2003b). It

was suggested that the effect of temperature on dielectric constant is a function of the

ratio of bound to free water. Zheng and others (1998) concluded that the process of

marination increased the dielectric loss factor and decreased penetration depth of

microwaves in seafood due to addition of salt and spices. They found that the temperature

difference from the surface to the center of marinated seafood was greater than that for

nonmarinated samples. Dielectric and thermophysical properties of meat batters showed

that the frequencies (microwave or radio) have a marked effect on dielectric properties

(Zhang and others 2004a).

9

More recently, the dielectric property profiles of chicken breast muscle were

studied (Zhuang and others 2007a; Zhuang and others 2007b). It was found that they

were dependent upon the radio wave and microwave frequencies as well as on the

temperature. Increasing frequency from 10 to 1,800 MHz resulted in decreasing values of

the dielectric constant and loss factor regardless of temperature in this range, chicken

breast muscle type, or deboning time. Both the deboning time and muscle type

significantly affect the average values of the loss tangent (tan = dielectric loss

factor/dielectric constant).

Another study on fresh and marinated chicken breast meat was done to measure

the dielectric properties at 27.12 MHz for a temperature range of 1ºC to 70ºC. It was

observed that the dielectric constant, loss factor and loss tangent increased across the

measured temperature range. The dielectric loss factor of marinated meat was three times

higher than that of fresh chicken breast meat. The penetration depth of marinated meat

was lower than that for fresh chicken breast meat (Lee and others 2008).

Applications of RF heating in Food Processing

Radio-frequency heating has various commercial applications in the food

industry. At present, some developments are being applied in the baking industry. Any

new application in the food industry will be in the value-added category of processed

foods (Tewari 2007).

Early applications of radio-frequency heating of foods were recognized in the

1940’s. The first attempts were to use RF energy to cook processed meat, to heat breads

10

and dehydrate vegetables (Kinn 1947; Moyer and Stotz 1947). This was followed by

application of RF energy to thaw frozen products in the 1960’s (Jason and Sanders 1962).

The latter authors applied RF heating to thaw herring and white fish on an industrial

scale. The next generation of commercial applications of RF energy was in the bakery

industry for final drying of cookies and crackers. RF heating is currently practiced in the

baking industry to remove excess moisture from products.

Several studies have been done to investigate the effect of RF heating on meat

products. Cooking and/or pasteurization of only a few selected meat products have been

investigated. It was reported that RF heating could be the most promising technique for

continuous pasteurization of sausage emulsions in terms of penetration depth, energy

efficiency and product quality (Houben and others 1991). Ryynänen (1995) concluded

that RF heating could be favorable for heating of cured whole meat products like hams as

mode of heating ions in solution, which are plentiful in a product to which salts have

been added. Laycock and others (2003) evaluated the influence of RF cooking on the

quality of ground, comminuted and muscle meat products after being heated to a center

temperature of 72ºC. They concluded that RF cooking of processed meat products

resulted in decreased cooking time, lower juice losses, acceptable color, water holding

capacity and texture. Another study on post-cooking temperature profiles of meat

emulsions (Zhang and others 2004b) suggested that uneven temperature distributions are

possible in RF cooked meat products. They found that the temperature differentials were

two fold higher within the RF cooked sample relative to its steam-cooked counterparts.

11

Recently, a study was done to develop a system for production of encased cooked

meats using RF heating (Brunton and others 2005). They also compared the quality of RF

heated products with those produced by commercial cooking methods. Zhang and others

(2006) developed a method for RF pasteurization of large diameter meat product in

casings (i.e. leg and shoulder ham) and compared the sensory attributes of RF pasteurized

products with conventionally pasteurized product. It was concluded that RF cooked hams

had significantly lower water holding capacities and higher yields compared to their

steam cooked counterparts. The differences in the quality between RF and steam-cooked

samples were found to be relatively minimal and could be reduced even further by

making minor adjustments to RF cooking procedures.

Meat Proteins

The muscle consists of 75% water, 20 %protein, 3%fat and 2% soluble nonprotein

substances. Muscle proteins are divided into three categories based mainly on their

solubility as myofibrillar, sarcoplasmic and stromal proteins. Myofibrillar or the SSP (salt

soluble proteins) comprise about 50-56% of the total skeletal muscle protein and are

insoluble in water, but can be extracted with concentrated salt solutions. Myosin is the

predominant salt soluble protein and is 50-55% followed by actin which is about 22% of

the total myofibrillar proteins (Sams 2001). Proteins mainly soluble in water are called

sarcoplasmic or WSP (water soluble proteins). They account for approximately 30-34%

of the total protein. They are soluble proteins of the sarcoplsma and consist of creatine

kinase, myoglobin and other enzymes of the glycolytic pathway. The remaining 10-15 %

12

of the proteins is connective tissue proteins. The connective tissue proteins, collagen,

reticulin and elastin are all fibrous proteins (Tornberg 2005).

Effect of Heating on Meat Proteins

Conformational changes of proteins occurring on heating are called denaturation.

The cooking temperature, where these changes occur is commonly called the

denaturation temperature and has been mostly investigated using the differential scanning

calorimeter (DSC). The unfolding of the proteins can be followed by optical rotary

dispersion (ORD) and circular dichroism (CD). Another structural change that occurs on

heating is protein-protein interaction, resulting in aggregation of proteins. This is studied

by turbidity measurements and loss in protein solubility. The gel forming ability and the

type of gels formed by proteins are studied using microstructural measurements

(Tornberg 2005).

Heating of meat results in the development of textural, color and flavor

characteristic of a cooked product. These changes are mainly attributed to the effect of

heat on proteins and fats in the meat. Myosin and actin (myofibrillar proteins) and also

collagen (main protein in connective tissue) are the major structural proteins present in

muscle foods, and thus the effect of heat on these proteins has a major influence on the

resulting texture of the cooked meat (Brunton and others 2006). Most of the sarcoplasmic

proteins aggregate between 40ºC and 60ºC, but for some of them the coagulation can

extend up to 90ºC. For myofibrillar proteins in solution, unfolding starts at 30-32ºC,

followed by protein-protein association at 36-40ºC and subsequent gelation at 45-50ºC.

13

At temperatures between 53ºC and 63ºC collagen denaturation occurs, followed by

collagen fiber shrinkage (Tornberg 2005).

Physical, Chemical and Functional Properties of Chicken Breast Meat

The major meat quality attributes are appearance, texture, juiciness, flavor and

functionality (Fletcher 2002). The color of raw or cooked meat is the primary

determinant of acceptability of meat in the market, while water-holding capacity strongly

influences the color of raw meat and texture of the cooked product. With increasing

trends in processing, meat functionality has increased in relative importance because of

its key role in determining the sensory quality of ready-to-eat products. Loss in

functionality of poultry breast meat is often associated with pale meat called as PSE

(pale, soft, exudative) meat. Factors affecting the color values of the breast meat include

early aging during processing and storage and the meat thickness. Several researches

have examined the differences in meat characteristics of normal and pale fillets selected

visually or using L*(lightness) values (Bianchi and others 2005). PSE meat is also

characterized by low moisture retention, soft texture and light appearance (Barbut and

others 2005). A good understanding of difference in quality properties related to color is

necessary in order to reduce the potential negative impact of meat color variation on

processed foods (Qiao and others 2002a). There is a strong relationship between muscle

pH and its effect on both color and functional properties (Qiao and others 2002b) .

Postmortem glycolysis results in lactic acid accumulation and hence decline in pH of

muscle from near to 7.0 at death, to almost 5.5 after 24 hours of storage in the walk-in-

cooler.

14

Thermal Effects on Meat Texture

Thermally processed shelf-stable meat is a good food source, but it must be tender

and moist for maximal consumer acceptance. Shear force value has often been used for

measurement of meat tenderness (Kong and others 2007). The effect of heat on proteins

in muscle foods, including denaturation, dissociation of myofibrillar proteins, transversal

and longitudinal shrinkage of meat fibers, aggregation and gel formation of sarcoplasmic

proteins and solubilization of connective tissue, has a major influence on resulting texture

of the cooked meat (Kong and others 2007; Murphy and Marks 2000; Wattanachant and

others 2005a; Wattanachant and others 2005b).

Factors affecting changes in meat tenderness during heating have been

investigated, and it has been stated that solubilization of connective tissue improved meat

tenderness, and heat-denaturation of myofibrillar proteins caused toughening (Kong and

others 2008). Collagen content and solubility determined the contribution of connective

tissue to meats toughness. Shrinking of connective tissue exerted pressure on the aqueous

solution in the extracellular void and expelled water, and the cooking loss was connected

to tenderness and rigidity of tissue (Palka and Daun 1999).

Process of Marination

Marinade solutions containing inorganic phosphates and NaCl are used to

enhance the quality of poultry and other muscle foods. These ingredients improve water-

holding capacity, reduce shrinkage and cooking loss, limit drip loss following defrosting,

and increase tenderness (Li and others 2000). In general, marinade solutions consists of

15

water, phosphate and salt, but might also consists of water binders to improve cook

yields, flavoring substances and antimicrobial agents in minute quantities. Tenderness of

meat products, along with juiciness, flavor and color are the main eating quality

characteristics that influence the consumer’s overall judgment of quality (Wood and

others 1995).

There are three methods for producing marinated products, which include

immersion, injection, and vacuum tumbling. Immersion, the oldest method, consists of

submerging the meat in the marinade and allowing the ingredients to penetrate the meat

through diffusion with the passage of time. This method is unreliable for the meat

industry because it does not provide regularity in distribution of the ingredients, and it is

not practical because it requires long processing times and limits the quantity of marinade

to be added.

Multineedle injection marination is perhaps the most widely used method because

it allows for dosing an exact quantity of the marinade, ensuring regularity in the products

without the time losses required for immersion. To inject a marinade, needles or probes

are inserted, and the marinade is injected as the probe or needles are withdrawn,

spreading the marinade throughout the piece (Sams 2001).

Vacuum tumbling is a method of marinating poultry meat to provide a ready-to-

cook, value-added product. Massaging and tumbling result in the extraction of protein

exudates (consisting mainly of the salt-soluble proteins actin and myosin), which promote

cohesion during thermal processing. Tumbling yields products with improved juiciness

and better slicing characteristics (Alvarado and McKee 2007).

16

Functions of Salt and Phosphate

Two of the most common ingredients in brines and marinades are NaCl and some

type of phosphate, most commonly sodium tripolyphosphate (STPP). Salt (NaCl or KCl)

is one of the oldest and most effective food preservatives used. Salt is included in poultry

meat formulations in order to 1) enhance product flavor, 2) increase moisture retention,

3) act as a synergist with STPP to extract salt-soluble proteins.

Phosphates vary in their solubility and effect on muscle pH, but generally,

alkaline phosphates improve water retention by shifting the pH further away from the

isoelectric point of the myofibrillar proteins and by unfolding muscle proteins, thereby

exposing more charged sites for water binding. When phosphates are used for increasing

water-holding properties of meat, the USDA requires that phosphate concentrations are no

higher than 0.5% of the finished product weight. Although there are many phosphates to

choose from, STPP remains the most commonly utilized in brine solutions because it is

easy to use and inexpensive (Alvarado and McKee 2007).

17

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22

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23

CHAPTER 3

RADIO-FREQUENCY APPLICATION IN PREHEATING OF MARINA TED

CHICKEN BREAST MEAT

Deshpande D, Singh RK, Toledo RT. To be submitted to Journal of Food Science

24

Abstract

Radio-frequency (RF) cooking is a form of dielectric heating in which products

are heated by subjecting them to an alternating electric field between two electrodes,

often parallel plate electrodes. Although similar to microwave heating, RF heating is

proposed to be more suitable for industrial heating of meats because of the greater

penetration depths possible with this technology. In this study, the process of preheating

marinated chicken breast meat in a 6 kW RF oven was optimized, by controlling various

parameters like the distance between electrodes, thickness of the product between two

parallel electrodes and the design of the product container. The best method for

presenting the product to the RF field was moving the product container in by the

conveyor belt so that the product was exposed to RF field while in motion. This system

ensures better heating uniformity of the product. A plastic material transparent to RF

waves, known as Ultem®, was procured and used as a product container. Use of this

product container resulted in very good heating rates compared to other product

containers used in this experiment. The cooked meat yields were determined as a function

of programmed preheating of marinated meat in the RF oven, followed by final cooking

of the product in conventional air oven. Warner-Bratzler shear tests were performed on

cooked samples to determine the quality of RF preheated product, and the quality of the

RF treated product was not much different from that of the product cooked directly in a

conventional air oven. Another experiment showed that when extra marinade was added

during preheating in RF oven, the product absorbed some part of it and the efficiency of

this pickup was determined by using the values of gain, purge, expressible moisture and

cook yields.

25

Keywords: Radio-Frequency heating, marinated chicken breast meat.

26

Introduction

Cooking of marinated meat is of great interest to processors in the poultry

industry. Conventional methods heat foods externally through conduction, convection or

radiation. The main disadvantages of conventional methods are longer cooking times and

non-uniform heating, because heat is transferred from outside to inside of the product.

Radio-frequency (RF) heating is a form of dielectric heating generated when the product

is subjected to an alternating electric field between two parallel electrodes. Therefore, RF

heating is a good alternative to these conventional methods because of its volumetric

form of heating in which heat is generated within the product, which reduces cooking

times and could potentially lead to more uniform heating. RF heating is similar to

microwave heating, and both are considered non-ionizing radiations, because they have

insufficient quantum energy (less than 10eV) to ionize biologically important atoms

(Piyasena and others 2003). Generally two frequencies (915 and 2450 MHz) are used for

microwave food processing and three frequencies (13.56, 27.12 and 40.68 MHz) are used

for radio-frequency food processing (Tewari and Juneja 2007). In both RF and

microwave heating, there is interaction of electromagnetic energy with matter, and hence

the dielectric properties of the materials involved are of the utmost importance. The

permittivity of material can be expressed as a complex quantity ( rrr jεεε ′′−′= ), the real

part of which is called the dielectric constant (rε ′ ), which represents the capability of the

material to store electric energy and the imaginary part, which is associated with the

dissipation of electric energy in the material and is called as the dielectric loss factor

( rε ′′ ). The loss tangent (tan δ = rε ′′ / rε ′ ), is also often used as an index of energy

dissipation or loss in a material exposed to RF or microwave electric fields. Another

27

important factor affecting dielectric heating is penetration depth. It is defined as the

distance an incident electromagnetic wave can penetrate beneath the surface of the

material where the power decreases to 1/e of the level at the surface. Few studies have

been done to measure the dielectric properties of chicken breast meat. Recently, the

dielectric properties of chicken breast muscle were studied (Zhuang and others 2007a;

Zhuang and others 2007b). It was found that the dielectric properties were dependent

upon the radio wave and microwave frequencies as well as on the temperature. Increasing

frequency from 10 to 1800 MHz resulted in decreasing values of the dielectric constant

and loss factor regardless of temperature in this range, chicken breast muscle type, or

time after deboning. Both the time after deboning and muscle type significantly affected

the average values of the loss tangent (tan = dielectric loss factor/dielectric constant).

Another study on fresh and marinated chicken breast meat was done to measure the

dielectric properties at 27.12 MHz in the temperature range of 1ºC to 70ºC. It was

observed that the dielectric constant, loss factor and loss tangent increased with

temperature through the temperature range of the measurement. The dielectric loss factor

of marinated meat was three times higher than that of fresh chicken breast meat. While

the penetration depth of marinated meat was lower than that for fresh chicken breast meat

(Lee and others 2008).

Several studies were conducted to investigate the effect of RF heating on meat

products. Cooking and/or pasteurization of only a few selected meat products have been

investigated. It is reported that RF heating could be the most promising technique for

continuous pasteurization of sausage emulsions in terms of penetration depth, energy

efficiency and product quality (Houben and others 1991). Ryynänen (1995) concluded

28

that RF heating could be favorable for heating of cured whole meat products like hams as

the mode of heating is by the depolarization of ions in solution, which are plentiful in a

product to which salts have been added. Laycock and others (2003) evaluated the

influence of RF cooking on the quality of ground, comminuted and muscle meat products

after being heated to a center temperature of 72ºC. They concluded that RF cooking of

processed meat products resulted in decreased cooking time, lower juice losses,

acceptable color, water holding capacity and texture. Another study on post-cooking

temperature profiles of meat emulsions (Zhang and others 2004) suggested that uneven

temperature distributions are possible in RF cooked meat products. They found that the

temperature differentials were two fold higher within the RF-cooked sample relative to its

steam-cooked counterparts.

Recently, a study was done to develop a system for production of cooked meats in

casings using RF heating (Brunton and others 2005). They also compared the quality of

RF-heated products with those produced by commercial cooking methods. Zhang and

others (2006) developed a method for RF pasteurization of large diameter meat product

in casings (i.e. leg and shoulder ham) and compared the sensory attributes of RF

pasteurized products with conventionally pasteurized product. It was concluded that RF

cooked hams had significantly lower water holding capacities and higher yields as

compared to their steam cooked counterparts. The differences in the quality between RF

and steam cooked samples were found to be relatively minimal and could be even further

reduced by making minor adjustments to the RF cooking procedures.

29

When marinated meat is cooked, physical and chemical changes occur that

change the binding of water in meat. Water held in the muscle is squeezed out during

cooking when collagenous membranes surrounding the muscle fibers and muscle fiber

bundle contract before the muscle protein gels. Thus, a scheduled heating sequence in the

cooking of meat would minimize the release of water and will result in the most juicy

cooked meat. The focus of this research was to optimize the process for preheating

marinated chicken breast meat when using a radio-frequency oven. The objectives of this

study are as follows:

(1) To determine the efficiency of marinade pickup using RF heating

(2) To optimize the process of preheating marinated chicken breast meat when using

a radio-frequency oven

30

Material and Methods

Sample preparation

Fresh chicken breast meat (sorted and trimmed to 113.3 gm pieces) was obtained

from a local commercial processing plant (Mar Jack Inc., Gainesville, GA). The initial

mass of fresh chicken breast meat was determined on a balance (Scale Systems Inc., IL)

and the meat was stored in a refrigerated room at 4ºC until it was used for further

processing. Marinade was prepared at room temperature at 22ºC by mixing 6% salt and

1.3% sodium tripolyphosphate (STPP) in desired amount of deionized (DI) water for

20% pick-up. The final concentration for salt and phosphate targeted in the product after

marination was 1% and 0.3% respectively. The marinade was then chilled at 4ºC until it

was ready for use. Chicken breast meat and the marinade were put together in a vacuum

tumbler (Model no. 1102, U-MEC Food Processing Equipment, CA) and 27 inches of

vacuum (692.30 mm Hg) was drawn with a high capacity vacuum pump. Tumbling was

conducted for 20 min at 8 rpm in a 7ºC processing room. The marinade addition was

targeted at 20% of meat weight. Immediately after tumbling, the mass of the marinated

meat was noted in order to determine the percent marinade absorption or the percentage

gain. The purge loss was calculated by determining the weight of samples after storing

for 24 h at 4ºC after marination. The pH and total moisture values of fresh chicken breast

meat, marinated meat and meat after 24h of storage were determined. Expressible

moisture was determined after 24h of storage. Two different experiments were performed

and the experimental design for both of them is described as follows:

31

Optimization of Marinade Retention by RF Preheating

This study was conducted to optimize the RF heating and vacuum tumbling

processes in order that the meat will absorb and hold marinade added during tumbling

and the additional marinade added to eliminate voids in the meat while heated in the RF

field. The RF oven was a Model S061B, Strayfield Fastran, UK. Four different

treatments were used. and each treatment was replicated twice. Ten percent (of green

weight) extra marinade was added in three treatments to determine the efficiency of

absorption while preheating in the RF oven. In treatments 1 and 2 (T1 and T2), the

samples were preheated in the RF oven to 30ºC. Immediately after preheating, they were

tumbled warm in the vacuum tumbler for 5 min for treatment 1, whereas they were

cooled in ice and tumbled for 2 min in treatment 2 (T2). In treatment 3 (T3), the

marinated meat at 5ºC was preheated in the RF oven to 20ºC, cooled with ice and then

vacuum tumbled for 2 min. In treatment 4 (T4), 30% of marinade was directly added to

fresh chicken breast meat and preheated in the RF oven to 30ºC and then vacuum

tumbled warm for 20 min immediately after RF treatment.

For the RF treatments, the marinated meat was put into Rubbermaid plastic

container (1.1 gal) for placement in the dielectric field. This container was used in all the

treatments. Preliminary experiments were conducted to determine the RF exposure

needed for the meat to reach the target temperature. Meat temperature was measured with

a type K thermocouple thermometer (Fisher Scientific) after the meat was removed from

the RF field. RF heating parameters were noted for each batch, which included the anode

current (Ia), grid current (Ig), distance between the electrodes, conveyor belt speed and

32

finally the RF heating rate. Immediately after, RF preheating, the mass of the meat

samples was determined and then the samples were stored in air-tight containers in the

cold room (4ºC) for 24 hours. The samples were again weighed after 24 h and the amount

of marinade lost as purge was recorded. The samples were then cooked in an air-

impingement oven (model no. 1450, Lincon Impinger, IN), until they reached the end-

point temperature of 80ºC. A Type K thermocouple probe was inserted in the thickest

part of the chicken breast meat to ascertain that the target endpoint temperature was

reached. In the reference treatment (control treatment), the vacuum tumbled batch was

directly cooked in the impingement air-oven after 24 hours at 4ºC and without RF

treatment. Results of the four RF treatments and the reference treatment were statistically

analyzed. The cooked meat yields for all the batches were determined after removal from

the impingement oven and equilibration to room temperature.

Optimization of Cook Yields by RF Preheating to Myofibrillar Protein Gelation

Temperature

This study was conducted to optimize cooked yield by preheating marinated

chicken breast meat in the RF field until the meat proteins were preset at 55-60ºC

followed by finial cooking to an internal temperature of 80ºC in a convection oven. A

Fiber-optic temperature-sensing device (UMI4, Universal Multichannel Instrument, Fiso

Technologies Inc., Canada) was used to measure and record time-temperature data during

RF heating. This study consisted of four treatments that were replicated four times. The

weight of each batch of breast meat was determined before heating in the RF oven.

Marinated chicken meat, prepared as described above, was used in this study. Meat at

33

4ºC was placed in the respective containers (Rubbermaid and Ultem) and exposed to the

RF field until the target end-point temperature between 55-60ºC was reached. This

temperature is the gelation temperature of the myofibrillar proteins. Immediately after RF

preheating, the meat was placed on an aluminum tray and cooked in a conventional air

oven (Blodgett, Dual Flow) at 176.6ºC until the center temperature reached 80ºC. The

meat temperature in the center of the thickest part of the meat was monitored using a type

K thermocouple. After the meat end-point temperature was reached, the meat was

allowed to equilibrate at room temperature and the cooked weight was measured. Six

breast pieces from each batch of cooked meat were then wrapped in aluminum foil and

the shear values were determined with a TA-XT2i texture analyzer. Results were reported

as the mean of each of the six samples for each batch.

For treatments 1, 3 and 4 a plastic material made of polyetherimide also known

as, Ultem® was procured and used as product carrier. The fiber-optic temperature

sensing probes were positioned, one at the geometric center and the other at the rear end

of the container in order to measure the temperature uniformity along the length of the

container. The tip of the probe was inserted in the thickest part of the breast meat. The

Ultem® container was made such that it matched the area of the upper electrode. For

treatment 1 (T1), the conveyor belt was moving at a set belt speed and the product was

exposed to RF as the container moved on the conveyor belt between two parallel plate

electrodes. After the first run, the RF oven was stopped for 2 min and again the product

was exposed to RF until it reached the target temperature of 55-60ºC. This was followed

by cooking the meat in a conventional oven until the end-point temperature of 80ºC was

reached and the final weight after cooking was determined. For treatment T3, the Ultem®

34

container was placed directly between the two plate parallel electrodes and the conveyor

belt was kept stationary. For treatment T4, the same Ultem® container was used and the

conveyor belt was kept moving at a variable belt speed. The meat was mixed in between

the two runs in order to ensure uniform temperature distribution at the end of RF

preheating. For treatment T2, a different container, i.e., the Rubbermaid plastic container

was used and the product was exposed to RF when the conveyor belt was on at a set belt

speed. This container was used in order to preheat three layers of product one above the

other and determine the uniformity of temperature distribution. The fiber optic probes

(Fiber Optic temperature Sensors, FISO technologies Inc, Canada) were placed such that

one of them was inserted into the meat piece on the top layer and the other one inside the

piece on the bottom layer of the product in the container. A control was used in which the

marinated meat was directly cooked on an aluminum tray in the convection oven until the

end-point temperature of 80ºC was reached. The temperature distribution of cooked meat

at different points along the length and width of an aluminum pan was noted and put in

the table in order to determine the nonuniformity of temperature distribution (Table 3.7).

Measurements of Meat Properties

pH

The pH of surface of chicken breast meat was measured with a direct probe

method, Accumet pH meter (AR15 pH meter, Fisher Scientific) equipped with a flat

probe (Accumet, Cat. no. 13-620-289) electrode. The pH meter probe was calibrated and

standardized (using pH 4.00 and pH 7.00 Buffer solutions) for every batch. The pH

values were obtained for fresh meat, marinated meat, RF preheated meat and meat after

35

24h of storage after marination. Triplicate measurements were made and values were

reported as the mean.

Total moisture

Total moisture values were determined with a Mettler Toledo moisture analyzer

(HR73 Moisture Analyzer, Mettler Toledo, Switzerland). About 4-5 grams of sample was

weighed on the aluminum pan. The drying temperature was set at 90ºC for the standard

drying cycle for about 3 to 4 h. Total percentage moisture values where obtained for fresh

chicken breast meat, marinated meat, RF preheated meat and meat after 24 h of storage.

Expressible Moisture

The Filter press method (Wierbicki and Deatherage 1958) was used for measuring

the water-holding capacity of the marinated meat after 24 hours of storage.

Samples )5300( ± mg of 24-h-stored marinated meat) were placed on a previously

weighed filter paper (Whatmann no. 1, 9 cm diameter). Then, the filter paper with meat

sample was placed between two Plexiglass plates. A load of 1.0 kg was applied for 1 min

and the damp filter paper was rapidly weighed after removing the compressed meat

sample. The mean of two replicates was taken as the average value for water holding

capacity, expressed as percentage of released water (expressible moisture, EM), and

calculated as:

EM= (wt. of damp filter paper – wt. of dry filter paper) × 100 / sample weight

36

Shear Value

Warner-Bratzler Shear tests were conducted on cooked chicken breast meat as

described by (Rababah and others 2005) using a TA- XT2i texture analyzer (Texture

Analyzer, Texture Technologies Corp.,NY). Samples were cooked, wrapped in aluminum

foil and equilibrated 30 min at room temperature (22ºC) as previously described. Cooked

chicken breast was cut parallel to the muscle fibers from the middle portion of the breast

to obtain a sample strip approximately 1.9 cm wide and 2.5 cm long. The sample

thickness was the natural thickness of the cooked meat. A slotted plate was installed into

a heavy-duty platform (TA 90) placed at the base of the texture analyzer and secured by

two thumbscrews. A shearing blade (TA 7 WB blade) was installed to load the cell

carrier. The heavy-duty platform was repositioned to enable the blade to pass through the

base plate. A 5-kg weight was used to calibrate the 25-kg load cell prior to the analysis

and the setting was adjusted at a preset speed of 5 mm/s, a test speed of 10 mm/s and a

posttest speed of 5 mm/s.

Shear test was conducted by loading the blade through the sample strip to

determine the maximum shear force (N) and the work of shearing (N s) based on the

force deformation curve. Average of six replicates was taken as the shear value for each

treatment.

37

% Marinade Pickup

Mass of fresh chicken breast meat was determined before marination.

Immediately after tumbling, the weight of marinated meat was determined and the

marinade absorption was calculated as follows:

MA = 1000 ×−

initial

initialh

W

WW………………………………………...………………… (3.1)

where, Winitial = green weight or initial weight of meat.

W0h= weight of marinated meat (at 0 h after marination)

Percentage Fluid Loss or Purge Loss

The samples were stored at 4ºC for 24 h and weighed. The percentage fluid loss

or purge loss of marinated mea was calculated as follows:

% FL = 10024 ×−

RF

RF

W

WW…………………………………………………………... (3.2)

where, W24= weight of marinated meat after 24 hours of storage.

WRF= weight of marinated meat after RF treatment.

Cook Yield

The samples were cooked as previously described. The whole batch was cooked

and cooked meat was allowed to equilibrate at room temperature and weighed. Cook

yields were calculated on green weight basis as follows:

% cook yield = (Wt. after cooking / Wt. initial) × 100 …………………………………... (3.3)

38

Statistical Analysis

Data were analyzed by using one-way Analysis of variance (ANOVA) and

Multiple Analysis of variance (MANOVA). The SAS jump software was used for this

purpose.

Results and Discussion

Optimized Marinade Retention

Results of measurements and one-way MANOVA resulted in the dendrogram

shown in Figure 3.1 and 3.2. The dendrogram was plotted using the MATLAB software.

The Y- axis of this plot is the mahalanobis distance which is used for statistical analysis.

The mahalanobis distance corrects data for different scales and correlations in the

variables. Since it has taken into consideration 4-5 different parameters in this experiment

in order to standardize them, it does not have a unit on Y-axis. The X-axis shows the four

different treatments and the control.

RF Preheating Parameters

Marinated chicken breast meat heated in Rubbermaid plastic container from 5ºC

to 30ºC required 25 min for treatments 1, 2 and 4 (with a heating rate of 1ºC/min), while

treatment 3 which was heated to 20ºC required 15 min. Cooking to a final end-point

temperature of 80ºC in an impingement oven for the reference treatment of marinated

non-RF preheated meat required 20 min from an initial temperature of 4ºC. This shows

that the RF heating was slower than conventional heating in an impingement oven. The

39

heating RF rates are dependent on various parameters such as distance between the

electrodes, product carrier, anode current and the grid current. The lesser the distance

between two parallel plate electrodes, the greater is the anode current and the heating

rates are faster. However, there is a limit to how far the electrodes can be spaced with the

product present in the gap. Arcing occurs and a strong arc will shut down the RF

generator. Electrode spacing was set at a point where arcing does not occur. When the

product was contained in a Rubbermaid container, the least possible distance between the

electrodes was 9.5cm without arcing. The anode current was 0.4 A and the grid current

was 0.74 A. One possible approach to increasing the RF heating rate will require the use

of a product container having the appropriate product depth and relatively low loss factor.

Percent Marinade Absorption (Gain)

Table 3.1 shows the percent of marinade absorption or the percentage gain for all

the treatments designed to maximize absorption of extra marinade added during the RF

preheating process. The gain values were found to be high for control i.e. around 27%.

Although more marinade was absorbed, all of it was not retained after 24 hours as the

expressible moisture values and the purge values were high compared to the other

treatments, which are discussed in detail in the following sections. A 3 to 4% gain was

obtained while the meat was RF preheated with the extra marinade. This was less than the

10% added marinade although there was no free marinade left when the meat and

marinade was removed from the container after RF treatment. These low values of gain

could be due to losses during the treatment (evaporation) and splashing of marinade as

the container was moved to the RF oven and positioned between the electrodes. In

40

addition, retumbling the meat after the RF treatment resulted in exudates of salt soluble

protein adhering to the walls of the tumbler and could not have been accounted for in the

final product weight. ANOVA results show that the percentage gain is not significantly

different in the four treatments and the control (p > 0.05). However, 3-4% gain in all four

treatments show that during RF preheating the extra marinade added gets absorbed with

further tumbling for 2-5 min. This could be an interesting inference for the poultry

industry.

Total Moisture

The total moisture values are given in Table 3.2. The total moisture was

maximum in RF-treated meat (Fresh meat < marinated meat < meat after RF treatment).

This proves that RF treatment promoted the absorption and retention of marinades in

chicken breast meat. The total moisture of chicken breast meat on wet basis was 78%

(Murphy and others 1998). In another study, the total moisture values for breast fillets

determined using the vacuum oven AOAC method was 76.35% (Qiao and others 2001).

In our study, the total moisture value was about 71% for fresh meat and 74% for

marinated meat. The difference in the total moisture values could be due to several

factors such as water absorbed during chilling, storage of meat in ice after deboning, or

wetting of the meat after deboning and also the method for determining the moisture

content. Mettler Toledo Moisture Analyzer, used in this study may also account for the

difference in values.

41

Percentage Fluid loss or “Purge” loss

The results of ANOVA for purge show that the p-value is very low (0.0002).

Hence, purge varied significantly with different treatments. Table 3.3 shows that the

purge is significantly different in treatment 3 and 4 as compared to the control treatment.

In treatment 3, the marinated chicken breast meat was preheated to a temperature of

20ºC. This temperature might not be sufficient to stimulate the absorption and retention

of marinade in the meat and hence the purge value is high. Whereas, in other treatments

the meat was preheated in the RF oven to 30ºC and at this temperature the marinade must

have been absorbed and retained after 24h.

pH

The pH value of marinated meat and meat after RF treatment was higher

compared to that of fresh chicken breast meat. The pH of marinated meat is given in table

3.3. Similar results were obtained in another study (Qiao and others 2002). They reported

the pH value for raw breast fillet as approximately 5.81, that of marinated fillet equal to

6.03 and the pH after cooking equal to 6.31. The ANOVA results (Table 3.4) show that

the p-value for pH is higher than 0.05 and hence it can be inferred that the pH does not

vary significantly with different treatments. The Tukey test also supports this

interpretation.

Expressible Moisture

The expressible moisture values for various treatments after 24h of storage are

reported in Table 3.3. Higher values of expressible moisture indicate lower water-holding

42

capacities. These results show that the expressible moisture in treatment 1 is significantly

different from the values obtained from the other 3 treatments and the control treatment.

The expressible moisture is lower in treatment 1 compared to its value in other

treatments. This indicates that the water absorbed during this RF treatment is retained in

the tissue. The expressible moisture value for the control is the highest. In another study

(Zhang and others 2004), EM values were reported to be significantly lower (P < 0.001)

for RF-cooked samples compared to steam-cooked samples. These findings were also in

agreement with those of Laycock and others (2003) for whole muscle and ground beef.

They reported that RF-heated whole muscle and ground beef samples had higher water-

holding capacities compared to their water-bath heated counterparts.

Cook Yield

P-value for cook yield across various treatments was less than 0.05. Thus, it can

be inferred that the cook yield is different from one or more treatments. The Tukey test

shows that cook yield from treatments 1 & 3 were statistically different from other

treatments and the control treatment. Cook yield value is high for treatment 1 as shown in

Table 3.3. The cook yields were calculated on the green weight basis. Zhang and others

(2006) concluded that the cook yield values for leg and shoulder ham for RF cooked

samples were higher than their steam-cooked counterparts.

43

Optimization of Cook Yields by RF Preheating to Myofibrillar Protein Gelation

Temperature

Time-Temperature Data for RF cooking

The dendogram of data analyzed statistically by MANOVA is shown in Figure

3.1 and 3.2. The Differential Scanning Calorimeter (DSC) showed a slight transition for

whole chicken breast meat at 55-57ºC. A study on meat proteins (Tornberg 2005)

reported that at temperatures between 53ºC and 63ºC collagen denaturation occurs

followed by collagen fiber shrinkage. Another study (Murphy and others 1998), showed

that chicken breast meat yielded three endothermic transitions, the first one at 53ºC and

the rest at 70 and 79ºC. Hence, in this study, the marinated meat was preheated in the RF

oven to around 55ºC in order to preset the proteins.

The typical time–temperature profile for RF-heated meat using Ultem® and

Rubbermaid plastic containers as product carriers are shown in Figure 3.3 and Figure 3.4

respectively. Figure 3.3 shows the time-temperature profile for preheating marinated

chicken breast meat in RF oven with Ultem® as the product carrier. Where position 1 is

position of fiber optic probe that was inserted in the meat piece at the center of the

Ultem® tray and position 2 is the position of fiber optic probe that was inserted in the

meat piece at the rear end of the Ultem® tray. Figure 3.4 shows the Time-Temperature

profile for preheating marinated chicken breast meat in RF oven with Rubbermaid

container as product carrier. Where, position 1 is the position of fiber optic probe that

was inserted in the meat piece at the bottom layer in the Rubbermaid container and

44

position 2 is the position of fiber optic probe that was inserted in the meat piece at the top

layer in the Rubbermaid container.

It can be inferred that the heating rates were faster when Ultem® was used as

product carrier as compared to Rubbermaid container. The time required to preheat the

meat to the target temperature in the RF oven using the Rubbermaid product carrier is

almost double that required for the product in Ultem® However, the temperature

distribution is uniform in case of treatment 2 (E2). Hence, the Rubbermaid container can

be used for RF preheating if uniform temperature distribution in different pieces along

the length of the container is desired. Table 3.5 shows the values of anode current (Ia)

and the cathode current (Ig). It can be inferred that as the distance between the electrodes

is reduced, the anode current (Ia) increases and the time required for RF preheating

decreases. Hence, in order to achieve faster heating rates, the distance between the upper

electrode and the product surface should be kept minimal.

Treatment 4 (E4) was conducted in order to obtain faster heating rates in

combination with uniform temperature distribution. The meat was mixed in between the

two runs while preheating in the RF oven. The oven was stopped for 5-7 min to rearrange

the meat and the temperature probes. Faster heating rates were achieved, however the

temperature distribution at the end of preheating was not as uniform as it was with the

Rubbermaid product container.

In the control, the marinated was directly cooked in a conventional air oven and

the time required for cooking to the final end-point temperature of 80ºC was

approximately 20 min. The temperature distribution along the length of the aluminum

45

tray after final cooking for the control is shown in Table 3.7. Zhang and others (2004),

studied the end-point temperature distribution for RF-cooked and steam-cooked pork

(Luncheon roll). These workers reported that for steam-cooked samples, the coldest point

was located at the geometrical center of the samples. In contrast, for RF-cooked samples,

the cold point was located at the part of the sample nearest to the bottom electrode. In our

study, for the Rubbermaid container as product carrier, the meat piece closest to the

bottom electrode was at higher temperature compared to the one on the surface. This

could be due to the gap between the surface layer of meat and the upper electrode and

due to evaporative loss as the container was not covered during cooking. Whereas, when

the Ultem® container was used as the product carrier, the meat at both ends of the tray i.e.

front and rear, was at the lower temperature compared to that of the center. The

temperature difference in this case along the length of the container was much more than

expected. This could be caused by many factors. The product in this experiment was

exposed to RF fields as a batch. In the case of continuous operation, it could be possible

to minimize this temperature difference. Another reason could be that the samples were

heated in air. The temperature difference could be due to the fact that samples could have

continually lost heat to the surroundings due to the lower temperature of surrounding air.

In addition, a lack of dielectric uniformity caused by areas of products with high capacity

for RF absorption can lead to runaway heating and even product arcing in these areas.

Widely varying temperature along the length of the container implies the need to change

the design of the product carrier. Zhang and others (2004), used a system in which

circulating hot water surrounded the system that held the comminuted meat product for

46

RF heating. These workers also reported temperature differentials, however they were

less in magnitude as those reported by (Laycock and others 2003).

Cook Yield

The cooked yield values for different treatments are given in Table 3.5. The cook

yield values were higher for treatment 1 and for control as compared to the other

treatments. The values are more than 100 as it was calculated on the green weight basis.

Similar values for cooked yields were obtained by Zhang and others (2006) for RF and

steam- cooked leg and shoulder ham. Statistical analysis using ANOVA (Table 3.6)

shows that the cook yield does not vary significantly in different treatments (p > 0.05).

Texture Analysis

Warner-Bratzler maximum shear force values and the work of shear for different

treatments are presented in Table 3.5. ANOVA table shows that the p-value for shear

force (N) and that for work of shear (N.s) are both less than 0.05 and hence these values

vary significantly with different treatments. The Tukey test results show that the shear

values for Treatment 2 (E2-Rubbermaid container as product carrier) are lower than that

for the other treatments. For the treatments where Ultem® was used as the product carrier,

there is no significant difference between the shear values obtained for RF preheated

meat and the control. However, in case of treatment E3, the shear values are

comparatively high. Work of shear was found to be same for all the treatments where

Ultem® was used as the product carrier. Similar values for work of shear were obtained

for treatment E2 (Rubbermaid container as product carrier) and the control.

47

Conclusion

Radio-frequency preheating of chicken meat has a great potential for the poultry

industry. Heating of meat to 55ºC using Ultem® as the product carrier resulted in faster

heating rates. The major advantage was to have all the pieces of uniform internal

temperature on entering the final heater and hence the target end-point temperature in the

final heater was reached at almost the same time for all the pieces. This avoided the over-

cooking of some meat pieces in the conventional process thus maximizing the cooked

product yield.

48

References

Brunton NP, Lyng JG, Li WQ, Cronin DA, Morgan D & McKenna B. 2005. Effect of

radio-frequency (RF) heating on the texture, colour and sensory properties of a

comminuted pork meat product. Food Res Int 38(3):337-344.

Houben J, Schoenmakers L, Vanputten E, Vanroon P & Krol B. 1991. Radio-frequency

pasteurization of sausage emulsions as a continuous process. J Microw Power

Electromagn Energy 26(4):202-205.

Laycock L, Piyasena P & Mittal GS. 2003. Radio-frequency cooking of ground,

comminuted and muscle meat products. Meat Sci 65(3):959-965.

Lee, Toledo & Nelson. 2008. The dielectric properties of fresh and marinated chicken

breast meat. Unpublished data Personal communication.

Murphy RY, Marks BP & Marcy JA. 1998. Apparent specific heat of chicken breast

patties and their constituent proteins by differential scanning calorimetry. J Food

Sci 63(1):88-91.

Piyasena P, Dussault C, Koutchma T, Ramaswamy HS & Awuah GB. 2003. Radio-

frequency heating of foods: Principles, applications and related properties - a

review. Crit Rev Food Sci Nutr 43(6):587-606.

Qiao M, Fletcher DL, Smith DP & Northcutt JK. 2001. The effect of broiler breast meat

color on ph, moisture, water-holding capacity, and emulsification capacity. Poult

Sci 80(5):676-680.

49

Qiao M, Fletcher DL, Smith DP & Northcutt JK. 2002. Effects of raw broiler breast meat

color variation on marination and cooked meat quality. Poult Sci 81(2):276-280.

Rababah T, Hettiarachchy NS, Eswaranandam S, Meullenet JF & Davis B. 2005. Sensory

evaluation of irradiated and nonirradiated poultry breast meat infused with plant

extracts. J Food Sci 70(3):S228-S235.

Ryynänen S. 1995. The electromagnetic properties of food materials: A review of the

basic principles. J Food Eng 26(4):409-429.

Tewari G & Juneja VK. 2007. Advances in thermal and non-thermal food preservation.

Blackwell Pub.



Wierbicki E & Deatherage FE. 1958. Determination of water-holding capacity of fresh

meats. J Agric Food Chem 6(5):387-392.

Zhang L, Lyng JG & Brunton NP. 2004. Effect of radio-frequency cooking on the

texture, colour and sensory properties of a large diameter comminuted meat

product. Meat Sci 68(2):257-268.

Zhang L, Lyng JG & Brunton NP. 2006. Quality of radio-frequency heated pork leg and

shoulder ham. J Food Eng 75(2):275-287.

50

Zhuang H, Nelson S, Trabelsi S & Savage E. 2007a. Effect of deboning time and muscle

type on dielectric properties of uncooked chicken breast meat at 50C. J Anim Sci

85:23-24.

Zhuang H, Nelson SO, Trabelsi S & Savage EM. 2007b. Dielectric properties of

uncooked chicken breast muscles from ten to one thousand eight hundred

megahertz(1). Poult Sci 86:2433-2440.

51

Table 3.1: Percentage gain for four different treatments

Treatment Gain (% Marinade Absorption)

Std. Deviation

T1 23.33 0.87

T2 23.45 0.27

T3 26.71 0.72

T4 24.10 0.89

Control 27.35 1.12

52

Table 3.2: Percentage total moisture (of fresh meat, marinated meat, meat after RF treatment and meat after 24 hours of storage) for different treatments

Treatment Fresh meat Marinated meat Meat after RF Treatment

T1 70.54 72.85 74.04

T2 70.38 73.61 75.16

T3 71.30 72.95 74.99

T4 70.58 72.95 73.69

53

Table 3.3: Effect of various treatments on purge, pH, expressible moisture and Cook yields

Treatment Purge 24 h %

pH 24 h Expressible

Moisture 24 h % Cook yield %

T1 0.01 (0.00)1 5.97 (0.06) 20.92 (0.40) 100.51 (0.85)

T2 0.02 (0.01) 5.88 (0.07) 31.31 (1.00) 96.11 (0.49)

T3 0.12 (0.01) 5.91 (0.08) 36.68 (1.67) 99.01 (2.47)

T4 0.01 (0.01) 5.86 (0.01) 36.59 (0.56) 92.38 (1.35)

Control 0.04 (0.01) 5.91 (0.01) 58.50 (2.12) 95.60 (2.00) 1Numbers in parentheses are standard deviations.

54

Table 3.4: ANOVA table for various parameters measured for four different treatments and control treatment (Design 1)

Parameter F Value Significance

Cook yield 7.78* < 0.05

Gain 2.16 0.21

Moisture 214.83* < 0.05

pH 1.1 0.44

Purge 60.93* < 0.05 .*indicates p value < 0.05, hence parameter varies significantly for different treatments

55

Table 3.5: Effect of Various Treatments on Gain, Cook Yields, Shear and Work of Shear.

Gain %

Ia (A)

Ig (A)

Dist. b/w electrodes

(cm)

Total cooking

time (min)

Cook Yield

%

Shear (N)

Work of

shear N.s.

E1 18.08 (1.00)

0.70 (0.00)

0.68 (0.00)

8.50 (0.00)

40.00 (0.00)

106.79 (7.44)

18.42 (0.32)

34.14 (1.08)

E2 18.36 (0.71)

0.40 (0.00)

0.74 (0.00)

10.50 (0.00)

55.00 (0.00)

105.29 (2.62)

15.00 (3.14)

28.49 (6.64)

E3 17.56 (0.77)

0.50 (0.00)

0.70 (0.00)

8.80 (0.00)

70.00 (0.00)

100.57 (3.35)

21.12 (0.91)

41.78 (2.54)

E4 19.08 (0.06)

0.65 (0.00)

0.68 (0.00)

9.00 (0.00)

45.00 (0.00)

104.18 (4.18)

18.07 (0.82)

35.87 (0.70)

Control 3.85

(0.75) 0.00

(0.00) 0.00

(0.00) 0.00

(0.00) 20.00 (0.00)

109.39 (4.08)

17.27 (2.88)

31.42 (5.72)

1Numbers in parentheses are standard deviations.

56

Table 3.6: ANOVA table for various parameters measured for four different treatments and control treatment (Design 2)

Parameter F Value Significance

Cook yield 1.98 0.15

Gain 313.06* < 0.05

Shear 4.94* < 0.05

Work of shear 5.92* < 0.05 *indicates p value < 0.05, hence parameter varies significantly for different treatments

57

Table 3.7: Temperature (ºC) distribution after final cooking in conventional air oven.

81.6 71.2 74.6

77.7 77.0 81.6

80.5 87.2 78.2

Picture showing the temperature distribution along the length of the aluminium tray after cooking in the conventional oven

58

Figure 3.1: Dendogram describing the relationship between different treatments and control based on the five testing parameters of pH, Gain, Moisture, Cook yield and Purge

59

Figure 3.2: Dendogram describing the relationship between different treatments and control based on Gain, Cook yield, Shear force and Work of Shear.

60

Time-temparature data

0

10

20

30

40

50

60

70

80

0 200 400 600 800 1000 1200 1400 1600

Time (s)

Tem

per

atur

e(C

)

position 1

position 2

Figure 3.3: Time-Temperature profile for preheating marinated chicken breast meat in RF oven with Ultem® as the product carrier

61

Time-temperature data

0

10

20

30

40

50

60

0 500 1000 1500 2000 2500

Time (s)

Tem

pera

ture

(C

)

position 1

position 2

Figure 3.4: Time-Temperature profile for preheating marinated chicken breast meat in RF oven with Rubbermaid container as product carrier.

63

CHAPTER 4

TEMPERATURE TRANSITIONS OF CHICKEN BREAST MEAT PROT EIN

FRACTIONS BY DIFFERENTIAL SCANNING CALORIMETRY

Deshpande D, Singh RK, Toledo RT. To be submitted to Journal of Food Science

64

Abstract

Poultry meat is comprised of 20-23% proteins, which consists of mainly

myofibrillar proteins, sarcoplasmic proteins and the connective tissue proteins.

Conformational changes on heating of protein are usually called denaturation and the

temperature where these changes occur is called the denaturation temperature. Heat

induced changes in proteins change water-holding capacity of meat. Meat can shrink in

two dimensions (length and width) and expand in the third dimension. The extent of meat

shrinkage and expansion varies with different types of muscles and meat temperatures.

The objectives of this study were: (1) Apply known procedures for extraction of

myofibrillar and sarcoplasmic proteins from the chicken breast meat and determine

difference in protein extractability between normal and PSE meat; and (2) Determine

temperature transitions in unmarinated whole muscle and its constituent proteins and in

heated marinated whole chicken breast muscle.

65

Introduction

Poultry meat is comprised of about 20-23% proteins, which are divided into three

categories based mainly on their solubility as myofibrillar, sarcoplasmic and stromal

proteins. Myofibrillar or the salt soluble proteins(SSP) comprise about 50-56% of the

total skeletal muscle protein and are insoluble in water but can be extracted with

concentrated salt solutions. Myosin is the predominant salt soluble protein and is 50-55%

followed by actin which is about 22% of the total myofibrillar protein (Sams 2001).

Proteins mainly soluble in water are called sarcoplasmic or water soluble proteins (WSP).

These consist of Creatine kinase, myoglobin and other enzymes. Stromal proteins which

constitute 3-5% of the total protein mainly consist of collagen and elastin (Belitz and

others 2004).

Functional properties of poultry meat are texture and water holding capacity

(WHC). Loss in functionality of poultry breast meat is often associated with pale meat

called as pale, soft, exudative (PSE) meat. Factors affecting the color values of the breast

meat include inadequate aging before deboning, time the meat was stored before

examination, and thickness of the meat. Several researchees have examined the

differences in characteristics of normal and pale fillets selected visually or using lightness

(L*) values (Bianchi and others 2005). Aside from color, PSE meat is characterized by

low moisture retention, softness and lack of springiness when poked with the finger, and

more reflective of light (Barbut and others 2005). A good understanding of difference in

quality attributes reflected by meat color is necessary in order to minimize the potentially

66

negative impact of meat color variation on foods prepared from the raw meat (Qiao and

others 2001).

Heating of meat results in the development of textural, color and flavor properties

characteristic of a cooked product. These changes result from thermally induced changes

in proteins and interactions with fats in the meat. Myosin and actin (myofibrillar proteins)

and also collagen (main protein in connective tissue) are the major structural proteins in

muscle foods. Thermal transitions of these proteins, the time span across and the high

temperature hold time after these transitions have major influences on the resulting

texture of the cooked meat (Brunton and others 2006). These effects include protein

denaturation, dissociation of myofibrillar proteins, shrinkage in length and width of meat

fibers, aggregation and gel formation of sarcoplasmic proteins and solubilization of

connective tissue (Kong and others 2007; Murphy and Marks 2000; Wattanachant and

others 2005a; Wattanachant and others 2005b). The solubilization of connective tissue

improves meat tenderness and heat denaturation of myofibrillar proteins causes

toughening (Kong and others 2008). Most of the water in the muscle is held by capillary

action by the myofibrils. When muscle is heated, proteins denature and release the

entrapped juice. The release of water and dissolved ions cause a detectable change in

dielectric properties and this can be used as a method to measure the protein denaturation

(Bircan and Barringer 2002).

Conformational changes on heating of protein are usually called denaturation and

the temperature where these changes occur is called the denaturation temperature. The

Differential Scanning Calorimeter (DSC) has mostly been used to determine the

67

denaturation temperatures of meat proteins (Tornberg 2005). The amount of denatured

proteins differs in normal and PSE muscle. The PSE muscle has a high drip loss, a very

pale color and contains denatured myofibrillar or sarcoplasmic proteins. The soluble

sarcoplasmic proteins are lower in PSE compared to normal muscle. Denatured muscle

proteins are less soluble than that of native proteins because insoluble aggregates are

formed on denaturation. It has been suggested that the light reflective and pale color of

PSE muscle is due to precipitation of denatured sarcoplasmic proteins. The precipitated

proteins mask the red color of the sarcoplasm producing the pale color. It was found that

the excessive paleness of PSE pork is due to closer packing of myofilaments at low pH

(Joo and others 1999). Another study (Van Laack and Lane 2000) suggested that myosin

from chicken breast is resistant to denaturation and hence the color of PSE chicken meat

is different from that of pork.

Heat induced changes in proteins change water-holding capacity of meat. Meat

can shrink in two dimensions (length and width) and expand in the third dimension. The

extent of meat shrinkage and expansion varies with different types of muscles and meat

temperatures. Loss of moisture also contributes to changes in sarcomere length and

juiciness as meat temperatures increase (Murphy and Marks 2000).

The objectives of this study were: (1) Apply known procedures for extraction of

myofibrillar and sarcoplasmic proteins from the chicken breast meat and determine

difference in protein extractability between normal and PSE meat; and (2) Determine

temperature transitions in unmarinated whole muscle and its constituent proteins and in

heated marinated whole chicken breast muscle.

68

Material and Methods

Samples

The chicken breast meat fillets were obtained from a local poultry processor

(Wayne Farms-DQH, Pendergras, GA). The samples were chopped in a food processor

prior to extraction. Extracts of sarcoplasmic and myofibrillar proteins were stored in the

freezer (4ºC) until used in further investigations and analysis.

Protein Solubility

To determine the solubility of sarcoplasmic and myofibrillar proteins, two

extractions were conducted as described by Joo et al. (1999) with some modifications.

Sarcoplasmic proteins were extracted from 2 gm of meat sample with 20 ml of 0.025M

sodium phosphate buffer (Buffer A, pH=7.2). The samples were homogenized with a

PRO300A Proscientific homogenizer (Sparks Technologies, Buford, GA) on ice with low

setting for 1 min. The samples were then centrifuged in a Sorvall RC-5B refrigerated

super-speed centrifuge with an SLC 1500 rotor ( Du Pont Instruments, Wilmington, DE)

at 8000 g for 20 min at 4ºC. The supernatant was collected and labeled as sarcoplasmic or

water soluble proteins. During extraction the samples were kept under cold conditions to

prevent the denaturation of proteins due to increase in temperature as well as to avoid the

inconsistency in results.

The pellets obtained were mixed with 0.025 M of sodium phosphate buffer,

pH=7.2 containing 0.6 M of NaCl (Buffer B) whicj was used for the extraction of

Myofibrillar proteins. This was followed by a similar process of homogenization of the

69

samples with low setting on ice for 1 min. To ensure proper solubilization of the salt

soluble proteins, the samples were left on a Corning PC 620 hot plate/stir plate (Fisher)

for 4 hours. The samples were placed on ice during stirring. Then they were centrifuged

at 8000 g for 20 min at 4ºC and the supernatants were labeled as myofibrillar or salt

soluble proteins.

Protein Quantification

The concentration of proteins in the supernatants was determined by using the

Better Bradford Assay (Coomassie Plus-The Better Bradford Assay Kit, PIERCE, IL)

with some changes described as follows. The samples were diluted with buffer in the

ratio of 1:20. 400 µl of the sarcoplasmic and myofibrillar protein sample was mixed with

7600 µl of buffer A and buffer B respectively. The protein standards were prepared using

BGG (Bovine Gamma Globulin) 2mg/ml (Product #23212 obtained from PIERCE).

BGG was used instead of BSA to get more accurate results. Instead of mixing the protein

standard and samples with the Coomassie Plus protein assay Reagent (product #

1856210, PIERCE) on the micro-plate, they were mixed in test tubes with the reagent

initially (20 µl of standard and sample with 600 µl of Coomassie Plus reagent) and then

about 310 µl of the above mixture was put on the micro-plate and the absorbance was

measured on a micro-plate reader using the Micro-plate Manager (Bio-Rad model 550

micro-plate reader, Hercules, CA) at 595nm.

70

Sodium Dodecyl Sulphate (SDS) gel electrophoresis

Sample preparation

Once the protein concentration was determined (using the Better Bradford Assay),

the samples were diluted to 8 mg/ml using the equation N1V1=N2V2. Dilution was carried

out by mixing the sarcoplasmic and myofibrillar supernatants with calculated amount of

Buffer A and Buffer B respectively (Table 4.4). This ensured that a constant amount of

protein, i.e., 20 µg was introduced on the gel for all the samples. The stock standard

sample buffer contained 8 M urea, 2 M thiourea, 3% (w/v) SDS, 75 mM D1-dithothreitol,

25mM Tris-HCl at pH= 6.8 and 0.1% bromophenol blue. This was mixed with β-

mercaptoethanol (25 µl in 475 µl of stock sample buffer) and was prepared immediately

before use. The samples were mixed 1:1 with standard sample buffer (300 µl of sample

and 300 µl of sample buffer) and were heated at 100ºC for 5 min in boiling water bath,

cooled to room temperature, centrifuged for a minute (using a Centrifuge 5412,

Brinkmann Instruments, N.Y) and applied on to the gel.

Electrophoresis conditions

The gel electrophoresis was carried out with the Pharmacia Biotech Phast System,

(Amersham Biosciences, Sweden). The system consists of a separation and control unit

and a development unit. The Fast Coomassie staining technique was used for detecting

proteins in Phast gel separation media using Phast gel blue R which is Coomassie R 350

dye in a tablet form. The solutions for the electrophoresis were prepared as follows: Stain

was made of 0.1% PhastGel Blue R solution in 30% methanol and 10% acetic acid in

71

distilled water (mili Q water). The stock solution was prepared initially and the final

solution was made fresh and used immediately. Destain consisted of 30% methanol and

10% acetic acid in distilled water (mili Q water). The Preserving solution was prepared

with 10% glycerol and 10% acetic acid in mili Q water. 4-15% gradient gel was used for

separation of myofibrillar proteins while the 8-25% was used for the sarcoplasmic

proteins. This was done because 8-25% gradient gel has smaller pore size which is

suitable for low molecular weights of sarcoplasmic proteins. While 4-15% gradient gels

has larger pore size, which is more suitable for high molecular weight proteins like

myosin and actin. The SDS buffer strips and the gradient gel were obtained from GE

healthcare biosciences AB,(Sweden).

Sample preparation for Thermal Denaturation

Extracts of the constituent proteins (i.e., water soluble, salt soluble proteins and

collagen) were removed from the freezer, allowed to thaw under refrigeration, and

dialyzed. The dialyzed retentate samples were stored at -80ºC for a couple of weeks. The

frozen samples were thawed before using them for thermal denaturation experiment.

Thermal Denaturation Experiment

The Differential Scanning Calorimeter (DSC, Mettler Toledo) was calibrated with

indium before measuring the denaturation temperatures of chicken breast meat and its

constituent proteins. Hermetic aluminum pans were used for sample measurement for

DSC. Approximately, 10-15 mg of the sample was placed in the pan. Empty aluminum

pans were used as reference. The samples were subjected to a heating rate of 10ºC/min in

72

the temperature range of 10-100ºC. The denaturation curves were obtained and the peak

denaturation temperatures were determined by analyzing three replicates for each sample

using the Mettler Toledo Star E software.

Results and Discussion

The pH and the L*(lightness), a*(redness), b* (yellowness) values were measured

24 hours post mortem. The L*, a*, b* values for the PSE samples were 60.55, 12.03 and

10.59 respectively and pH was 5.58. The normal sample had L*, a*, b* values of 57.87,

11.97 and 13.92 respectively and pH of 5.85.

The procedure used for extraction of sarcoplasmic and myofibrillar proteins from

the normal and PSE muscle was relatively easy to perform, and ample quantities of

protein were recovered in the extracts. Stirring the homogenized mixture on ice for 4

hours increased the amount of myofibrillar proteins extracted. The Better Bradford

Assay was used to compare the protein concentration in normal and PSE muscle. The

standard curve for standard proteins was plotted by using the absorbance values (greater

than 0.05 and smaller than 0.7) given in Table 4.1. The standard curve had a slope of

0.6149 and the correlation coefficient was 0.9793 (Figure 4.1).

The extract of PSE muscle had lower protein concentration compared to the

normal muscle extract. The concentration of sarcoplasmic proteins and myofibrillar

proteins were 12.2 mg/ml and 16.6 mg/ml, respectively, in the pale muscle extract. On

the other hand, concentration in the normal muscle extract was 13 mg/ml and 20.4

mg/ml, respectively for sarcoplasmic and myofibrillar proteins. The summary of the

73

Assay is listed in Table 4.3. The numbers 3 and 19 indicate the different samples of meat

obtained from the local farm. The concentration of sarcoplasmic proteins (WSP) is lower

as compared to that of myofibrillar proteins (SSP) in both the normal and PSE samples,

which is in agreement with the data given in the literature. Protein solubility affects some

of the physical properties of the meat therefore the differences between PSE and normal

meat will have consequences in how these two types of muscles will respond to

processing procedures. (Qiao and others 2002) reported that light chicken breast meat has

significantly lower total protein value than normal or dark meat.

The different proteins extracted were investigated by performing SDS-PAGE. The

molecular weights of the protein subunits were determined with a densitometer (Model

GS-700 Imaging Densitometer, Bio-Rad Laboratories) by comparison of the relative

mobility of migration with those of protein molecular weight standards. Rf values were

calculated as follows:

Rf = (Distance of band from origin) / (Distance from the origin to the reference point).

The distances were measured with a scale. The gels were scanned by using the

Molecular Analyst software (Windows software for Bio-Rad’s image analysis systems

version 1.5). Scanning densitometers with software installed readily integrate the stained

band or spot relative to the total staining intensity of the entire gel or a part of it (Barany

and others 1995).By using the equation of the calibration curve, the molecular weights

for the unknown protein sub fractions were determined as shown in Table 4.6 and Table

4.7.

74

The scanned picture of the gels is shown in Figure 4.4. Figure 4.4 (a) shows the

electrophoresis profile for sarcoplasmic (WSP) proteins. The bands were observed in

similar locations for all four samples in this experiment except for the intensity of the

bands in different lanes. Lane 2 and 4 are the electrophoretic patterns of extracts from

pale and normal samples, respectively, with the extraction procedure previously

described. Lane 3 and 5 are the patterns for extracts of pale and normal samples,

respectively, when a different extraction procedure was used. Thus the first band is

darker for lanes 2 and 4 as compared to the first band in lanes 3 and 5. For myofibrillar

proteins shown in Figure 4.4 (b), slight difference was observed in the position of one

band for the pale and normal sample. The estimated molecular weights of the two

distinctly dark bands seen for both the pale and normal samples were approximately 210

kDa and 35 kDa (Table 4.7). The molecular weight of heavy-chain Myosin is 200 kDa

and that of actin in its monomeric form of G-actin has molecular weight of 42 kDa

(Murphy and Marks 2000). Hence the first dark protein band for both the pale and

normal samples in this experiment could be assumed as Myosin heavy chain (MW 210)

followed by the myosin light chains. Actin is not degraded by proteolytic enzymes and is

resistant to denaturation. Hence, the amount of actin present in the sample is directly

related to the amount of sample spotted in the electrophoresis gel. In another study, (Van

Laack and others 2000), it was found that the extracts of pale and normal breast meat

contained similar quantities of phosphorylase in the myofibrillar fraction, indicating that

protein denaturation has occurred in pale and normal muscles. (Barbut and others 2005)

reported that the myofibril fragments in extracts of PSE chicken breast meat subjected to

SDS-PAGE had some missing bands in the area corresponding to the high molecular

75

weight protein. This could be because the extent of soluble myosin was lower in PSE

compared to normal muscle. From the results of SDS-PAGE, they confirmed that the

protein denaturation was more extensive in PSE meat than in dark meat. Another study

on the pork samples, (Joo and others 1999) showed that the pre-rigor conditions in PSE

muscle caused precipitation of the sarcoplasmic proteins, which are most sensitive to pH

and temperature conditions, post mortem and led to the hypothesis that the early

conditions after death (pH and temperature) play an important role in determining the

color of the meat. They also confirmed that the pork color was associated with the

precipitation of sarcoplasmic proteins on the myofibrillar proteins.

The results of denaturation study of chicken breast meat and its constituent

proteins are given in Table 3.8. The Graph of temperature (ºC) vs. heat flow (milliwatts)

was obtained for each sample, and the peak denaturation temperatures were determined

for each sample. Fresh chicken breast meat had two peak transitions, one at 58ºC and

another at 77ºC. Three peak transitions were obtained for sarcoplasmic protein fraction,

at 27ºC, 52ºC and 75ºC. For myofibrillar proteins, there was a single huge peak obtained

around 59ºC. The stromal proteins failed to show a transition peak on the DSC

thermogram obtained. This could be due to the low concentration of collagen present in

chicken breast meat as compared to the other proteins. The thermal denaturation study for

marinated chicken breast meat (stored for 24h) gave a peak transition at 55.27ºC. This is

shown in figure 4.5.

A study was done on DSC to obtain the apparent specific heat of chicken breast

meat and its constituent proteins (Murphy and others 1998). These workers found that

76

chicken breast meat yielded three endothermic transitions, with peak transition

temperatures of 53, 70 and 79ºC. These endothermic transitions in chicken breast patties

corresponded to the denaturation of myofibrillar (53ºC) and sarcoplasmic (70 and 79ºC)

proteins.

Another review (Tornberg 2005) stated that most of the sarcoplasmic proteins

aggregate between 40 and 60ºC, but for some of them the coagulation can extend up to

90ºC. For myofibrillar proteins in solution, unfolding starts at 30-32ºC, followed by

protein-protein association at 36-40ºC and subsequent gelation at 45-50ºC. At

temperatures between 53 and 63ºC the collagen denaturation occurs, followed by

collagen fiber shrinkage.

Conclusion

From this study it can be concluded that the protein concentration of sarcoplasmic

protein is less than that of myofibrillar protein in chicken breast muscle. It was also found

that the protein solubility differed in normal and PSE muscle. The PSE muscle showed

lower protein solubility as compared to the normal muscle, which was assumed to be

caused by the denaturation of some of the protein fractions in PSE muscle. The results of

SDS-PAGE did not show much variance in the protein profiles of the pale and normal

samples of the chicken breast meat, indicating that the solubilized protein in the pale and

normal samples was similar. Further research can be done to study the cause of difference

in the protein profiles generated by the different extraction methods used. Thermal

denaturation determined by differential Scanning Calorimeter, identified thermal

transition peaks, which could be of value in designing a scheduled heating sequence for

77

cooking of chicken breast meat in RF and conventional ovens to obtain the most juicy

cooked meat.

78

References

Barany K, Barany M & Giometti CS. 1995. Polyacrylamide-gel electrophoretic methods

in the separation of structural muscle proteins. J Chromatogr A 698(1-2):301-332.

Barbut S, Zhang L & Marcone M. 2005. Effects of pale, normal, and dark chicken breast

meat on microstructure, extractable proteins, and cooking of marinated fillets.

Poult Sci 84(5):797-802.

Belitz HD, Grosch W & Schieberle P. 2004. Food chemistry,3rd rev. ed. Berlin ; New

York: Springer.

Bianchi M, Fletcher DL & Smith DP. 2005. Physical and functional properties of intact

and ground pale broiler breast meat. Poult Sci 84(5):803-808.

Bircan C & Barringer SA. 2002. Determination of protein denaturation of muscle foods

using the dielectric properties. J Food Sci 67(1):202-205.

Brunton NP, Lyng JG, Zhang L & Jacquier JC. 2006. The use of dielectric properties and

other physical analyses for assessing protein denaturation in beef biceps femoris

muscle during cooking from 5 to 85 0C. Meat Sci 72(2):236-244.

Joo ST, Kauffman RG, Kim BC & Park GB. 1999. The relationship of sarcoplasmic and

myofibrillar protein solubility to colour and water-holding capacity in porcine

longissimus muscle. Meat Sci 52(3):291-297.

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Kong F, Tang J, Lin M & Rasco B. 2008. Thermal effects on chicken and salmon

muscles: Tenderness, cook loss, area shrinkage, collagen solubility and

microstructure. LWT - Food Science and Technology 41(7):1210-1222.

Kong FB, Tang JM, Rasco B & Crapo C. 2007. Kinetics of salmon quality changes

during thermal processing. J Food Eng 83:510-520.

Murphy RY & Marks BP. 2000. Effect of meat temperature on proteins, texture, and

cook loss for ground chicken breast patties. Poult Sci 79(1):99-104.

Murphy RY, Marks BP & Marcy JA. 1998. Apparent specific heat of chicken breast

patties and their constituent proteins by differential scanning calorimetry. J Food

Sci 63(1):88-91.

Qiao M, Fletcher DL, Smith DP & Northcutt JK. 2001. The effect of broiler breast meat

color on ph, moisture, water-holding capacity, and emulsification capacity. Poult

Sci 80(5):676-680.

Qiao M, Fletcher DL, Smith DP & Northcutt JK. 2002. Effects of raw broiler breast meat

color variation on marination and cooked meat quality. Poult Sci 81(2):276-280.

Sams AR. 2001. Poultry meat processing. Boca Raton, Fla.: CRC Press.



80

Van Laack R & Lane JL. 2000. Denaturation of myofibrillar proteins from chicken as

affected by ph, temperature, and adenosine triphosphate concentration. Poult Sci

79(1):105-109.

Van Laack R, Liu CH, Smith MO & Loveday HD. 2000. Characteristics of pale, soft,

exudative broiler breast meat. Poult Sci 79(7):1057-1061.

Wattanachant S, Benjakul S & Ledward DA. 2005a. Effect of heat treatment on changes

in texture, structure and properties of Thai indigenous chicken muscle. Food

Chem 93(2):337-348.

Wattanachant S, Benjakul S & Ledward DA. 2005b. Microstructure and thermal

characteristics of Thai indigenous and broiler chicken muscles. Poult Sci

84(2):328-336.

81

Table 4.1: Absorbance readings (at 595nm) for standard proteins (Better Bradford Assay)

Standard (µg protein) Absorbance Abs – blank 2 1.592 1.263

1.5 1.358 1.029 1 1.257 0.928

0.75 0.874 0.545 0.5 0.757 0.428 0.25 0.57 0.241 0.125 0.457 0.128 0.075 0.422 0.093 0.025 0.338 0.009

0 0.329 0

82

Table 4.2: Absorbance Readings and Protein concentration for Water Soluble and Salt Soluble Proteins (1µg/ µl = 1 mg/ml).

Sample 3(WSP) Abs Abs-blank

µg protein/µl

with dil factor Avg std dev

Mg/ml mg/ml a 0.608 0.279 0.33 6.57 b 0.671 0.342 0.42 8.41 7.891 1.15 c 0.681 0.352 0.43 8.7

Sample

19(WSP) Abs Abs-blank µg

protein/µl with dil factor Avg std dev

Mg/ml mg/ml a 0.745 0.416 0.53 10.6 b 0.684 0.355 0.44 8.79 10.39 1.52 c 0.788 0.459 0.59 11.8

Sample 3(SSP) Abs Abs-blank

µg protein/µl


mg/ml mg/ml a 0.749 0.42 0.53 10.7 b 0.8 0.471 0.61 12.2 12.23 1.57 c 0.857 0.528 0.69 13.8

Sample 19(SSP) Abs Abs-blank

µg protein/µl


mg/ml mg/ml a 0.783 0.454 0.58 11.7 b 0.821 0.492 0.64 12.8 12.23 0.55 c 0.802 0.473 0.61 12.2

a, b and c are replicates for each sample. 3 and 19 are numbers for different types of chicken breast meat.

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Table 4.3: Summary of the Better Bradford Assay

Sample number

Class WSP (mg/ml) Sarcoplasmic

proteins

SSP (mg/ml) Myofibrillar

proteins

3 Pale 12.2 16.6

19 Normal 13.0 20.4

3 and 19 are numbers for different types of chicken breast meat.

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Table 4.4: Protein concentrations diluted to 8 mg/ml for all samples to get constant protein (20 micro-grams on the gel)

Sample Avg protein mg/ml

dil (N1V1=N2V2)

(ml) protein to be added

(µl)protein to be added

buffer (µl)

WSP3 12.2 0.656 0.656 656 344.262

WSP19 13 0.615 0.615 615 384.615

SSP3 16.6 0.482 0.482 482 518.072

SSP19 20.4 0.392 0.392 392 607.843 3 and 19 are numbers for different types of chicken breast meat.

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Table 4.5: Rf values and log MW for calibration curve of both gels

Standard protein Distance Rf Distance Rf log MW

MW

WSP (cm) WSP SSP(cm) SSP Myosin 0.5 0.1 1.3 0.27 5.301 200000 B-galactosidase 1 0.2 2 0.41 5.0654 116250 Phosphorylase b 1.2 0.24 2.3 0.47 4.9886 97400 Serum Albumin 1.7 0.35 2.8 0.57 4.8209 66200 Ovalbumin 2 0.41 3.1 0.63 4.6532 45000 Carbonic anhydrase 2.7 0.55 3.8 0.78 4.4914 31000 Trypsin Inhibitor 3.3 0.67 4.2 0.86 4.3324 21500 Lyzozyme 3.6 0.73 4.5 0.92 4.1584 14400 Aprotinin 3.9 0.8 4.7 0.96 3.8129 6500

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Table 4.6: Molecular weights (MW) as estimated for the unknown sarcoplasmic protein subunits on gel 1

Dist (cm) Rf Log MW MW

(calculated)

1.2 0.245 5.012 102813

1.7 0.347 4.8206 66162

1.8 0.367 4.7823 60579

2.1 0.429 4.6675 46500

2.2 0.449 4.6292 42576

2.3 0.469 4.5909 38984

2.8 0.571 4.3994 25087

2.9 0.592 4.3612 22970

3.1 0.633 4.2846 19257

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Table 4.7: Molecular weights (MW) as estimated for the unknown myofibrillar protein subunits on gel 2

Pale CBM Rf

Log Mw MW

Normal CBM Rf

Log MW MW

(cm) (calculated) (cm) (calculated) 1.4 0.286 5.3226 210205 1.4 0.286 5.3226 210205 2.3 0.469 4.9716 93671 2.3 0.469 4.9716 93671 2.4 0.49 4.9326 85625 2.4 0.49 4.9326 85625 3.4 0.694 4.5426 34879 3.4 0.694 4.5426 34879 3.6 0.735 4.4646 29144 3.6 0.735 4.4646 29144 3.9 0.796 4.3475 22261 3.9 0.796 4.3475 22261 4 0.816 4.3085 20349 4.1 0.837 4.2695 18601

4.3 0.878 4.1915 15543 4.3 0.878 4.1915 15543 4.6 0.939 4.0745 11872 4.6 0.939 4.0745 11872

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Table 4.8: Peak denaturation temperatures for chicken breast meat and its constituent proteins

Tp1 (ºC) Tp2 (ºC) Tp3 (ºC)

1.Fresh chicken breast meat 58.08 77.77 --

2.WSP(water soluble proteins) 27 52.47 75.84

3.SSP (salt soluble proteins) 59.57 -- --

4. Marinated chicken breast meat

55.68 88.88 --

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Standard curve y = 0.6149x + 0.0146R2 = 0.9793

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 0.2 0.4 0.6 0.8 1 1.2

standard protein

abso

rban

ce

Figure 4.1: Standard curve for meat proteins obtained by The Better Bradford Assay.

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Calibration curve(for gel 1)

y = -1.8761x + 5.4715R2 = 0.9699

0

1

2

3

4

5

6

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Rf

log

MW

Figure 4.2: Calibration curve for Rf vs. Log MW for gel 1.

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Calibration curve(for gel 2) y = -1.9112x + 5.8687

R2 = 0.9559

0

1

2

3

4

5

6

0 0.2 0.4 0.6 0.8 1 1.2

Rf

Log M

W

Figure 4.3: Calibration curve for Rf vs. Log Molecular Weight for gel 2

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4.4a (WSP): Lane 1&6 STD, 7-BSA, 2&3-Pale samples Fig 4.4b (SSP): Lane 1,4 & 8 – Std, 2-pale, 4&5 – Normal samples. 3- Normal sample

Figure 4.4: Plot of Rf vs. Log MW for gel 2.

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Integral -5.13 mJ normalized -0.36 Jg^-1Onset 87.63 °CPeak 88.88 °CEndset 91.66 °C

Integral -1.45 mJ normalized -0.10 Jg^-1Onset 52.58 °CPeak 55.27 °CEndset 57.77 °C

[]MCBM 2MCBM 2, 14.1900 mg

mW

-11.5

-11.0

-10.5

-10.0

-9.5

-9.0

-8.5

°C30 40 50 60 70 80 90

ê x oê x oê x oê x o M CBM 2M CBM 2M CBM 2M CBM 2 2 4 .0 6 .2 0 0 8 1 9 :3 3 :3 02 4 .0 6 .2 0 0 8 1 9 :3 3 :3 02 4 .0 6 .2 0 0 8 1 9 :3 3 :3 02 4 .0 6 .2 0 0 8 1 9 :3 3 :3 0

SSSST AT AT AT ARRRR eeee SW 9 .1 0 SW 9 .1 0 SW 9 .1 0 SW 9 .1 0F o o d Sci ence s L a b: M ETT L ERF o o d Sci ence s L a b: M ETT L ERF o o d Sci ence s L a b: M ETT L ERF o o d Sci ence s L a b: M ETT L ER Figure 4.5: Transition peaks for marinated chicken breast meat

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CHAPTER 5

CONCLUSIONS

Thermal denaturation study on marinated chicken breast meat gave a scheduled

heating sequence for cooking in RF and conventional oven. The process of pre-heating

marinated chicken breast meat was optimized using RF oven. Heating of meat to preset

the proteins using Ultem® as the product carrier resulted in faster heating rates. Uniform

temperature distribution was achieved when Rubbermaid plastic container was used as

product carrier. Preheating of marinated chicken breast meat using RF has a great

potential for meat Industry provided the design be optimized so that the problem of

arcing is minimized.

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