Thermal processingThermal processing

Sterilization/pasteurizationSterilization/pasteurization

AppertizationAppertization

CanningCanning

History

1810 Nicolas Appert about 1860 Luis Pasteur provides scientific

explanation 1920 Bigelow and coworkers described method

of calculation 1945 Otto Rahn applies the principle that

microorganisms die according to logarithmic order.

HEAT is the energy in transit due to a temperature difference between two regions and is always transferred from the region of higher temperature to the region of lower temperature.

Conduction

Convection

Radiation

HEAT TRANSFER MODES:

Transport of energy due to direct molecular interaction without appreciable displacement of molecules.

CONDUCTION

Transport of energy from one point of fluid to another point by actual movement of fluid itself.

MODES OF CONVECTION:Natural convection Forced convection

CONVECTION

Transport of energy in the form of electromagnetic waves between materials across the space.

RADIATION

Process of putting a temperature sensitive element in food container and gathering temperature data over a time course during a thermal process. Reports on penetration tests need to state the type of thermocouple used and where the thermocouple was placed.

HEAT PENETRATION TEST

For penetration test the thermocouple should be placed in the coldest place of the container

for conduction heating product it is located at a geometric center of container

for convection heating products it is located 1/10 to 1/5 of the container height from the bottom of the container

Primary Objectives of Canning are:

to kill microorganisms

to keep away microorganisms

public health hazard

economic spoilage

Microorganisms:

Clostridium botulinum is the main public hazard b/c spores are heat resistant. Spores may survive when heat processing is insufficient. The health hazard is due to ability of Cl. botulinum to grow under anaerobic conditions and to produce toxin.

Public health hazardPublic health hazard

Economic spoilage is due to un-processing:Economic spoilage is due to un-processing:

sporeformers from the genera sporeformers from the genera BacillusBacillus

sporeformers from the genera sporeformers from the genera DesulfotomaculumDesulfotomaculum

sporeformers from the genera sporeformers from the genera ClostridiumClostridium

FOOD CONTAINERS:

Metal containers

Glass containers

Retort pouches

Double seamDouble seam

HEADSPACE

GROSS - vertical distance from the top of double seam or the top edge of the glass jar to the level of product in the container.

NET - vertical distance from the level of food to the inside surface of the lid (only metal containers).

A retort pouch does not have a true headspace, what is of importance is the volume of non con- densible gases.

Sterilization >100 oC

Pasteurization < 100 oC

Classification of thermal processes based on processing temperature

Terminal processes

Aseptic processes

Hot pack/hot fill processes

Classification of thermal processing based on method of product packaging

Food classificationFood classification

Low acid food pH > 4.6 Low acid food pH > 4.6 Acid food pH Acid food pH 4.6 4.6

““Acid” FoodsAcid” Foods

pH pH ≤≤ 4.6 4.6 Generally all fruitsGenerally all fruits Tomatoes, with added acidTomatoes, with added acid Sauerkraut and fermented picklesSauerkraut and fermented pickles Foods to which large amounts of acid are Foods to which large amounts of acid are

addedadded

““Low Acid” FoodsLow Acid” Foods

pH > 4.6pH > 4.6 Generally all vegetablesGenerally all vegetables MeatsMeats PoultryPoultry SeafoodSeafood SoupsSoups Mixed canned foodsMixed canned foods

Retorting consist of :Retorting consist of :

heating phase: heating phase: removal of air, come-up time removal of air, come-up time (CUT) , holding time at processing (CUT) , holding time at processing temperaturetemperature

cooling phasecooling phase

Types of retorts:Types of retorts:

Still retorts (nonagitating retorts): vertical, Still retorts (nonagitating retorts): vertical, horizontal, malo, hydrostatic.horizontal, malo, hydrostatic.

Agitating retorts: sterilmatic, orbitort, Agitating retorts: sterilmatic, orbitort, rotomat, rotomat,

Flame sterilizersFlame sterilizers Aseptic systemsAseptic systems

Still retort - vertical retortStill retort - vertical retort

Still retort -hydrostatic retortStill retort -hydrostatic retort

Agitating retort - Sterilmatic

Agitating Retort - ORBITORTAgitating Retort - ORBITORT

Effect of heat on Effect of heat on microorganismsmicroorganisms

Yeast are the least resistant, followed by mold and then bacteria. All vegetative cells are destroyed instantly at 100 0C . Spores of C. botulinum, C. sporogenes, C. bifermentans, C. butiricum, C. pasteurianum, C. perfringens,C. thermosaccharolyticum, D. nigrificans, and B. stearothermophilus are very heat resistance.

Equivalent processing timesEquivalent processing times

330 min at 100 330 min at 100 ooCC 150 min at 104 150 min at 104 ooCC 36 min at 110 36 min at 110 ooCC 10 min at 116 10 min at 116 ooCC 5.27 min at 118 5.27 min at 118 ooCC 2.78 min at 121 2.78 min at 121 ooCC 1.45 min at 124 1.45 min at 124 ooCC 0.78 min at 127 0.78 min at 127 ooCC

The destruction of microorganisms The destruction of microorganisms is affected by:is affected by:

their inherent resistancetheir inherent resistance by environmental influences during the by environmental influences during the

growth and formationgrowth and formation the heating time & temperaturethe heating time & temperature pHpH humidityhumidity protective effect of food components: fat, protective effect of food components: fat,

proteins, saltproteins, salt

Order of destruction of microorganismsOrder of destruction of microorganisms

The death of bacteria exposed to wet heat The death of bacteria exposed to wet heat is of logarithmic order.is of logarithmic order.

The logarithmic order means that theoreti- The logarithmic order means that theoreti- cally the survivors can be reduced to less cally the survivors can be reduced to less than one. Thus the number of survivors than one. Thus the number of survivors may become very small such as one may become very small such as one survivor in million units etc.survivor in million units etc.

The survivor curveThe survivor curve

The number of viable bacteria plotted on the logarithmic scale against the corresponding heating time (processing time) on the linear scale provides the graph known as the survivor curve.

DECIMAL REDUCTION TIME, DECIMAL REDUCTION TIME, DDTT

The time in minutes required to reduce the viable cells in suspension of bacteria to one tenth of their original value. The slope of semilogarithmic survivor curve determi -nes the decimal reduction time.

The logarithmic model for microbial The logarithmic model for microbial destruction is described by the destruction is described by the

equationequation

U =DT *(log N0 - log Nu)

U - the equivalent heating time at proces- sing temperature N0 - the initial numbers of microorga- nismsNu -the number of microrganisms after heating

Survivor Curves at Different Survivor Curves at Different Temperatures.Temperatures.

Comparison of D for Microbial PopulationComparison of D for Microbial Population

THERMAL DEATH TIMETHERMAL DEATH TIME

The longest time when the unit test are positive for growth and the shortest time when the units are negative

The thermal death (TDT) curveThe thermal death (TDT) curve

The value of F plotted on the logarithmic scale against the corresponding tempe- ra ture on the linear scale provides graph known as TDT curve.

Thermal Death Time CurveThermal Death Time Curve

The thermal resistance curveThe thermal resistance curve

Values of DT plotted on the logarithmic scale against the corresponding temperature on the linear scale provide a graph called phantom thermal death time curve or thermal resistance curve.

Parameter ZParameter Z

The parameter Z represents the number of degrees of Fahrenheit, centigrade, or Kelvin necessary to cause the F-value or D value to change by a factor ten.

TDT curve is described by TDT curve is described by equation:equation:

Log FT = ( Tref - T)/Z + Log Fref

Z = 10/log Q10

Q10 - 2.2- 4.6 dry heatQ10 - 8 - 20 wet heat

Lethal rateLethal rate

It is described as minutes at T ref per minute at T. Can be calculated using the following equation:

L = Fref/FT = 10 (T -Tret)/ Z

Z = 10 C or 18 F, Tref = 121.1 C or 250 F

Sterilization value of heat Sterilization value of heat process, Fprocess, F

F = Dref * (log N0 - log NF )

F = t * Li

F = ∫ L *dt