EFFECT OF VARIES HOMOGENIZATION PRESSURES AND DIFFERENT NON-FAT MILK SOLIDS ON ICE CREAM MADE FROM PALM KERNEL OILPresented by LIM SENG LEONG148139SV : Dr. Norashikin Abd. Aziz

Chapter 1Introduction

Introduction• According to Clarke (2004), the term ‘ice cream’ covers a

wide range of frozen desserts. The main ones are dairy ice cream, non-dairy ice cream, gelato, frozen yogurt, milk ice, sorbet, sherbet, water ice and fruit ice.

• In accordance to section 83, Food Regulation 1985, ice cream is a milk product that prepared by milk.

• Most of the ice cream manufacturers in Malaysia are using palm oil as the main ingredient to produce ice cream due to the availability of palm oil in Malaysia and limited supply of fresh milk either internally or externally (Wan Rosnani, 2004).

• Even though most of the ice cream in Malaysia is prepared by using vegetable oil, but it is still considered as ice cream because it contains skimmed milk powder.

• The interest of this study is concentrate on the economy ice cream that containing 10% fat (palm kernel olein) which is easily found in the market of Malaysia.

Problem statement• From the literatures had done, ice cream possesses a very

high market value either globally or in Malaysia (Datamonitor, 2011).

• Thus, there is a need to improve the quality of palm based ice cream due to its great potential in the global market.

• One of the most important parameter that will affect the quality of the ice cream is homogenization pressure.

• There are few studies that investigates the effect of homogenization pressure on ice cream (Koxholt et al., 2001; Tosaki et al., 2009; Reid & Skinner, 1929; Schmidt & Smith, 1989).

• However, most of the studies are done on the ice cream made from dairy fat. Thus, the effect of homogenization pressure on palm based ice cream is yet to be investigated.

• Other than processing parameter, the formulation or ingredient especially non-fat milk solid (NMS) that used to produce ice cream is also a very important factor in determining quality of ice cream.

• The main source of NMS are skimmed milk powder (SMP).• However, high cost of SMP caused many alternate sources

of NMS have been studied to replace part or all of the SMP. • There are two newly developed skimmed milk powder

replacer in the market and its use in making ice cream are yet to be determined.

Objective• Specific objective of the studies are:

▫To study the effect of the homogenization condition on the physical properties of palm based non-dairy ice cream.

▫To study the effect of non-fat milk solids substitutes on the physical properties of palm based non-dairy ice cream.

Chapter 2Literature Review

Making of ice cream

(Adapted from Goff , 2006)

Homogenization and structure development• Stogo (1998) stated that homogenization will prevent the fat

separation and improve the texture of the ice cream. • Ice cream mixes that undergo homogenization will decreased in

fat particles size and form a homogenized emulsion (Tosaki et al., 2009).

• This process will reduce the fat particle size to 2 µm and definitely increase the surface area of fat globules in the mix (Marshall et al., 2003).

• The proteins and emulsifiers will then readily absorb on the newly formed fat globules surface. The oil-water interfacial tension be reduced and form a stable emulsion (Marshall et al., 2003).

• Goff (2007) proposed that homogenization pressure for a 10% dairy fat ice cream mix at pressures of 17/3.5 MPa should yield appropriately sized fat globules optimal for fat structure development and stability.

• The ice cream mix that do not undergo homogenization will results in high degree of fat destabilization which is not favor the stable structure of ice cream.

Non-fat milk solids and its function

• The functions of NMS in ice cream are stabilize water-continuous emulsions and foams because they are surface active and contribute to the dairy flavor (Clarke, 2004).

• The newly formed fat globule exits the homogenizer devoid of any protective membrane. Protein particles will immediately adsorb onto the interface around the perimeter of the globule, forming a stabilizing protein membrane (Goff, 1997).

• The proteins introduce an electrostatic and steric stabilizing mechanism, preventing inter-droplet interactions upon collision.

• The amount of NMS in ice cream is about 9-12% depends on the formulation.

• The added amount of NMS to an ice cream mix is a primary factor for improving the quality of ice cream (Campbel & Marshall, 1975).

• Stamponi et al. (1996) also indicated NMS can cause a decrease in coldness, ice crystal and melting rate perception and an increase in creaminess and mouth coating.

Sources of non-fat milk solids• NMS can be obtained from few sources and raw

materials, which are skimmed milk powder (SMP), butter milk, condensed whole milk and whey protein powder (Clarke, 2004).

• Pelan et al. (1997) proven that ice cream mixes made from the skimmed milk powder produce a more stable emulsion comparing to other sources of NMS.

• However, the higher price of SMP is always the constraint for manufacturer to use hundred percent SMP in producing ice cream. Therefore, there are more and more alternate sources of NMS are available in the market to replace SMP.

Skimmed milk powder replacer(SMR)

• Most of the replacers are made from blends of whey protein concentrates, caseinates, and whey powders (Goff, 1995).

• The protein contents are normally less than skimmed milk powder (34%) to reduce the costs of production.

• SMR are used as one to one replacer• Most of the formulations of the SMR produced by

different company are distinguish. The constituents are normally kept secret and only the percentage of proteins and lactose are provided.

• The researches on the substitution or replacement of the skimmed milk powders are based on the protein level of the non-fat milk solids (Goff, 1997; Patino et al., 1995; Tcholakova et al., 2006; Patel et al., 2006; Gelin et al., 1996).

Emulsion stability and fat coalescence

• Ice cream mixes is oil in water emulsion, thus it is very fundamental to understand the emulsion formed during the processing of ice cream.

• The fat particles tend to fuse together and resulted in agglomeration or coalescence. There are 3 types of coalescence :

Fat Droplets: (a) Complete coalesce (b) Partially coalesce (c) Cannot coalesce

•Fat coalescence occurred at two stages:▫Prior ageing process▫Freezing process

Fat coalescence prior ageing process• Fat globules size reduced after coming out from

homogenizer and the surface area increase resulted in surface contact between fat globules and water increase and thus surface tension increase.

• To reduce the surface tension, they promptly fuse together to form a larger fat globules (McClements, 2005).

• Types of coalescence occurred are complete coalescence as the fat particles are all in liquid form.

• It may lead to separation of fat from the emulsion. So, a stable emulsions need to be produced to avoid complete coalescence.

Fat coalescence during freezing process• After sufficient time of ageing, the fat globules in ice

cream mixes are partially crystallize (semi solid). • Fat particles collide to each other and cause different

types of coalescence due to the shear effect by the dasher. • Unlike fat coalescence prior ageing process, the

coalescence occur can be any of the three results: (a) Complete coalesce (b) Partially coalesce (c) Cannot coalesce

• Complete coalesce or not coalesce are not favorable during freezing process.

• During freezing process, certain degree of fat destabilization (partial coalescence) is essential to develop an internal structure of agglomerated fat, which favorably alters the texture and physical appearance of the product (Goff, 1997).

• The interconnected droplets also form bridges between the air cells and form mechanical mousse-like foam.

Stages Prior ageing process

Freezing process

Types of fat coalescence present

Complete coalescence

Complete coalescence

Partial coalescence

Cannot coalesced

 Condition Static Strong

beating by dasher

Strong beating by dasher

Strong beating by

dasherReason Low

concentration of protein cause high interfacial

surface tension between

water and fat

Low protein concentration/

excess emulsifier

cause instability

under strong beating

Sufficient emulsifier and milk protein

cause relatively unstable emulsion

High protein concentration

cause emulsion too

stable   

Favorable Not favorable

Not favorable Favorable Not favorable

Effect Flocculation and unstable

emulsion formed may lead to fat separation

Large coalesced fat

globules formed and

unable to form firm 3-D network

Preferable partial

coalescence and 3-D network formed

Not enough fat

destabilized, coarse and unstable structure formed

Figure : The ice cream structure with 3-D fat network that trap the air bubbles

•In conclusion, ice cream mixes must be stable enough to prohibit complete coalescence of fat globules during aging process, but less stable to promote partial coalescence during the freezing process (Marshall et al., 2003).

Chapter 3Methodology

• The flow chart of the project works

Mixing

Pasteurisation

(70 oC for 30 minutes)

Pre-homogenized

Homogenization

Ice cream mixes analyses

Ageing

(> 4 hours at 0-4 oC)

Batch Freezing

(10 minutes)

Hardening

(-28 oC for 30 minutes)

Storage (-18 oC)

Frozen ice creams analyses

Mixes Formulation

Fat sourcePalm kernel OleinShortening

SweetenersSucroseGlucose

NMS source/substitutes

Skimmed Milk Powder (SMP—34 %wt protein)Dry Whey Protein

Others

Salt

Stabilizer-emulsifier blend

Water

A. The effect of varies homogenization pressures on physical properties of ice cream• The experiment was done by preparing 6 different

batches (3 replicates and 3 liter each) of ice cream (with above mixes formulation) and undergo a two stages homogenization at different pressure, which are :I. 0/0 MPaII. 5/5 MPaIII. 10/5 MPaIV. 15/5 MPaV. 20/5 MPa VI. 25/5 MPa.

B. The effect of different non-fat milk solids substitutes on physical properties of ice cream

• The experiment was done by preparing 3 different batches (3 replicates and 3 liter each) of ice cream by using different non-fat milk solids source, which are :▫ skimmed milk powder replacer A (SMR A- 15 %wt protein)▫ skimmed milk powder replacer B (SMR B- 19 %wt protein)▫ skimmed milk powder (SMP-34 %wt protein).

Ice cream mixes analyses• Total solids

▫ Direct oven drying method (Milk Market Administrators Office, 2012)

▫ Approximately 3g of ice cream mix pipetted directly into a pre-weighed sample dish.

▫ The weight of the dishes and ice cream mix were recorded. ▫ The petri dish with ice cream mix inside was then dried in the oven

for 4 hours.▫ The weight of each petri dish with dried ice cream was weighed and

recorded.

• Density▫The density of ice cream mixes (4oC) were determined

by using a pycnometer (SG-10 Pycnometer bottle, Gilson Company Inc., Ohio) (Tosaki et al., 2009). Total of three replicates were measured for each treatment.

• Mix Viscosity▫The apparent viscosities of the mixes (4oC) were

determined by using a viscometer (Brookfield programmable DV-II+ viscometer, Brookfield Engineering, USA).

▫Total of three replicates were measured for each treatment.

• Fat particle sizes of ice cream mixes▫ The fat particle sizes in ice cream mixes (4oC) samples were measured

by integrated light scattering using Mastersizer 2000 (Malvern Instruments, Malvern, UK).

▫ Measurements were carried out under ambient temperature with the dilution of emulsion in the sample chamber being approximately 1: 1000 with Milli-Q water.

▫ By referring to the method used by Velasco and Goff (2011), the refractive index chosen for the solid/liquid droplets and the dispersing medium was 1.46 and 1.33, respectively, with absorbance of 0.001 and obscuration value in the range 12-18%.

▫ The volume weighted median diameter (d50,3), fat particles sizes at cumulative volume of 90th percentile (d90) and surface weighted mean diameter (d3,2) were recorded.

Frozen ice cream analyses• Overrun

▫The overrun of ice cream was determined by weight (Marshall et al., 2003).

▫The ice cream mixes were filled into the 500ml plastic container and weighed

▫The frozen ice cream were filled into the 500ml plastic containers and weighed as well

▫Overrun calculated as follow

• Fat particle sizes of frozen ice cream▫The ice cream were first drawn from the freezer and

tempered at 4oC for 4 hours in a refrigerator. ▫Same as method use to measure fat particles in ice

cream mixes

• Meltdown properties▫ Meltdown properties of ice cream were determined by

using Bolliger et al. (2000) method.▫ The ice cream were removed from the containers and

weighed on a weighing scale. ▫ Then, the samples were placed on a 10 mesh grid (which

is 10 holes per 2.54cm) and allowed to stand at room temperature (25oC).

▫ The weight of ice cream that passed through the wire mesh was recorded regularly in an interval of 10 minutes for 90 minutes.

• Hardness▫ Ice creams were tempered at room temperature (25oC) for 10

minutes.▫ Texture analysis was conducted using a texture analyzer

(TA.XT2 Texture Analyzer, Stable Micro Systems, Reading, UK) fitted with a 5-mm diameter stainless steel probe.

▫ The force used to penetrate the ice cream sample to a depth of 25mm was recorded.

▫ The speed was set to 1mm/s2. ▫ Hardness was measured as the peak compression force (N)

during the penetration of the samples (El-Nagar et al., 2002).

• Turbidity test▫ The samples were analyzed for turbidity by spectroturbidity

(Golf & Jordan, 1989)▫ The frozen ice cream samples were removed from the

freezer and thawed at 0-4oC for 24 hours in a refrigerator.▫ The ice cream were first diluted to get a 1:500 dilution.▫ The absorbance of the sample was measured by using a

spectrophotometer (Ultrospec 3100 Pro UV-visible spectrophotometer, GE Healthcare Inc., USA).

▫ The same method applied on the ice cream mixes to find difference of absorbance in ice cream mixes and frozen ice cream.

Statistical Analysis• Results including the total solids, density, viscosity, overrun,

turbidity and hardness were reported as the mean obtained from ice cream prepared in triplicate.

• Statistical analyses were performed with SPSS 17.0 (IBM Software, USA).

• Analysis of variance was obtained using One-way ANOVA routines and multiple comparisons of means were conducted using T-tests (Tukey HSD multiple comparisons test).

• Statistical significance was given in terms of P values, with differences at the 95% confidence interval (P<0.05) considered as statistically significant.

Chapter 4Results and discussion

A. Evaluating effects of varies homogenization pressurea) Effect on the physical properties of ice

cream mixes.b) Effect on the fat destabilization of ice

cream.c) Effect on the physical properties of

frozen ice creams.

Effect on the physical properties of ice cream mixes

Treatment Pressure (MPa)

Density (g/cm3) Total Solids (%)

1 0/0 1.099a 34.4a

2 5/5 1.099a 34.5a

3 10/5 1.098a 34.5a

4 15/5 1.098a 34.1a

5 20/5 1.099a 35.0a

6 25/5 1.098a 34.6a

Effect of homogenization pressure on density and total solids

*Presented values are the means of triplicate.*Values within a column not sharing a common letter (a, b, c, etc.) differ significantly, P < 0.05.

• Total solids content is defined as the sum of the ingredients other than water (Clarke, 2004).

• Total solids and density of ice cream are always depend on the formulation of ice cream.

• Since same formulation are used for all the 6 treatments, thus there is no effect on the total solids and density.

Pressure(MPa) D10(µm) D50(µm) D90(µm)0/0 1.240 3.791 14.6635/5 0.587 1.534 3.87910/5 0.683 1.469 3.48915/5 0.662 1.444 3.24820/5 0.667 1.541 3.56125/5 0.749 1.655 3.936

Effect of homogenization pressures on fat particles sizes in ice cream mixes

0/0 5/5 10/5 15/5 20/5 25/51.000

1.500

2.000

2.500

3.000

3.500

4.000

Homogenization Pressure(MPa)

Par

ticl

e S

ize,

D50

(µm

)

Effect of homogenization pressures on fat particles sizes in ice cream mixes

• The decrease in fat particles sizes as homogenization pressure of the ice cream mix increase from 0Mpa to 15Mpa is due the increase in mechanical strength that breaks the fat particles into smaller sizes.

• However, the fat globules sizes increase slightly from 15Mpa to 25Mpa indicates that small portion of fat globules size in the ice cream mixes undergo complete coalescence after homogenization

• It is predicted that, the homogenized pressure at 20/5 Mpa and 25/5 Mpa produced fat globules which are too small and cause the oil-water interfacial tension to increase. But, the proteins present are not susceptible to cover all the fat globules area in a very short time.

• Thus, fat globules in homogenized ice cream mixes tend to agglomerate in order to reduce the oil-water interfacial tension

0/0 5/5 10/5 15/5 20/5 25/570

90

110

130

150

170

190

Homogenization Pressure(MPa)

Vis

cosi

ty(m

Pa.

s)

Effect of homogenization pressures on viscosity of ice cream mixes

• High viscosity in the un-homogenized ice cream mixes is because of the high internal resistance due to the big globules and linear chains of globules that present (Schmidt and Smith, 1989).

• The increase of homogenization pressure from 5/5 Mpa to 25/5 Mpa cause the viscosity of ice cream increase significantly.

• Clark (2004) stated in his book of ‘The Science of Ice Cream”, the increasing homogenization pressure will increase the mix viscosity. Thomsen & Holstborg (1997) reported that the same trend as in this studies, the mixes viscosity increased with the homogenization pressure applied.

• These previous studies totally support the results obtained.

Comparison between fat particles sizes in ice cream and ice cream mixes

Pressure (MPa)

D50(µm) D90(µm)Ice cream

mixesIce cream Ice cream

mixesIce

cream0/0 3.791 23.466 14.663 80.9085/5 1.534 3.879 3.879 21.037

10/5 1.469 3.753 3.489 18.58615/5 1.444 2.515 3.248 16.52620/5 1.541 2.508 3.561 16.21625/5 1.655 2.414 3.936 15.834

Effect on the fat destabilization of ice cream

• At the same pressure, the fat particles sizes is increase from ice cream mixes to frozen ice cream.

• Increase in size is due to the fat destabilization and the coalescence occur during the freezing process.

• the ice cream mixes that homogenized at higher pressure is relatively more stable and do not undergo much fat destabilization compare to ice cream mixes homogenized at low pressure.

• Un-homogenized ice cream mixes possess very large fat particles size. This is because the large fat particles size in ice cream mix and the lack of ability to maintain the stability of the emulsion form. The fat globules easily clustered when external force exerted during freezing process.

0/0 5/5 10/5 15/5 20/5 25/50.0%

5.0%

10.0%

15.0%

20.0%

25.0%

30.0%

35.0%

40.0%

45.0%

Different Homogenization Pressure(MPa)

Fat

Agl

omer

atio

n in

dex

(F

AI/

%)

Effect of homogenization pressures on fat agglomeration index

• the agglomeration index decrease as homogenization pressure increase, although the difference between 20/5 Mpa and 25/5 Mpa is not significant statistically (P>0.05).

• The bigger the fat particles size or fat aggregate formed, the higher the degree of fat destabilization.

• This result is totally agreed with the work done by Schmidt & Smith (1989).

Effect on the physical properties of frozen ice creams.

0 5 10 15 20 2520.0%

30.0%

40.0%

50.0%

60.0%

70.0%

80.0%

90.0%

100.0%

Homogenization Pressure (Mpa)

Ove

rru

n(%

)

Effect of homogenization pressures on overrun of ice cream

• There are few studies that reflected the overrun of dairy ice cream is highly dependent on the fat destabilization index.

• Bolliger et al., (2000) shows that there is little increase of overrun as the destabilization of fat globules increase with the presence of different level of emulsification.

• However, our results show the opposite trend, the increase in destabilization level decrease the overrun of the ice creams.

• These may due to the different fat source that used in this study.

• Velasco & Goff (2010) reported the same trend as our results in their studies that using sunflower oil and palm kernel olein.

• According to Velasco & Goff (2010), the extensive formation of partial coalescence in ice cream displaced protein from the air-water interface during freezing or whipping, thus hindering the foamability of ice cream.

• This results also supported by Marshall et al., (2003), certain degree of destabilization of fat globules is needed in ice cream, but over destabilization might lead to the complete coalescence rather than partial coalescence which will resulted in unstable ice cream structure.

• Thus, we can conclude that low homogenization pressure will cause the emulsion (ice cream mixes) become less stable. Instability of mixes favor the complete coalescence rather than partial coalescence of ice cream mixes. The coarse structure will produce ice cream with low formability (Muse & Hartel, 2004).

Effect of homogenization pressures on hardness of ice cream

Homogenization Pressure (MPa)

Resistance to Penetration (N)

0/0 10.1a

5/5 4.7b

10/5 5.6c

15/5 6.3cd

20/5 6.5d

25/5 7.2d

*Presented values are the means of triplicate.*Values within a column not sharing a common letter (a, b, c, etc.) differ significantly, P < 0.05.

• The un-homogenized ice cream has the highest resistance to penetration due to its lowest overrun.

• The increase of hardness is due to the increase of the stability of the ice cream structure that formed (Tosaki et al., 2009).

• The increase in stability is proven by the increase of the overrun of the ice cream with the increase of homogenization pressures.

• The structure that is more stable enables the ice cream more firms to resist rupture.

0 10 20 30 40 50 60 70 80 900%

10%

20%

30%

40%

50%

60%

70%

80%

90%

0/0Mpa5/5Mpa10/5Mpa15/5Mpa20/5Mpa25/5Mpa

Time elapsed (minutes)

Mas

s L

ost(

%)

Effect of homogenization pressures on meltdown properties of ice cream

• The total mass loss of ice cream decreases gradually as the homogenization pressure increase.

• It was thus likely that the stable fat structures could hold melted water, which led to slower meltdown.

• Muse & Hartel (2004) proposed that increased overrun may be the reason for changes in heat transfer across the ice cream. Air is an effective insulator, increasing amount of air in the ice cream will increase the melt stability by slowing the rate of heat transfer in it.

• This result is supported by the research done by Koxholt et at. (2001) and Sakurai (2003)

B. Evaluating effects of different skimmed milk powder replacersa) Effect on the physical properties of ice

cream mixes.b) Effect on the fat destabilization of ice

cream.c) Effect on the physical properties of

frozen ice creams.

Effect on the physical properties of ice cream mixes.

SMR A SMR B SMP0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

30.0%

35.0%

40.0%

Density total solid

NMS source

Den

sity

(g/

cm3)

Tot

al S

olid

(%

)

Effect of skimmed milk powder replacers on density and total solids of ice cream mixes

• Even though the ice cream mixes were formulated accordingly by using different type of NMS, but the density and total solids of the ice cream is almost same for each treatment.

• This is because SMR A and SMP B substitute the SMP with the ratio of 1:1. Same mass of SMR A and SMR B are used, thus changes in formulation do not alter the total solids and density of ice cream mixes.

NMS D10 (µm) D50 (µm) D90

(µm)D3,2 (µm)

SMR A 0.738 1.594 5.873 1.412SMR B 0.713 1.556 4.830 1.360

SMP 0.683 1.469 3.489 1.275

Effect of skimmed milk powder replacers on fat particles sizes in ice cream mixes

• The size of fat particles size increase in the order of SMP<SMRB< SMRA.

• The large D90 values reflect that the fat globules in the ice cream mixes undergo complete coalescence where the small fat globules combine to form a large fat globule.

• High degree of coalescence is actually indicating the emulsion formed after homogenization is very unstable (Marshall et al., 2003).

• By considering the protein level as the predominant factor to determine the fat particles size, the fat particles size increase as the protein level decrease.

• This result is actually totally agreed with the work done by Goff (1997) and Tcholakova et al., (2006).

• At low concentration of protein in ice cream, there is insufficient of protein that able to cover the fat globules. As the results, the small fat particles started to rearrange to form a more stable structure by complete coalescence.

SMR A SMR B SMP0

20

40

60

80

100

120

140

160

NMS sources

Vis

cosi

ty (

mP

a.s)

Effect of skimmed milk powder replacers on viscosity of ice cream mixes.

• By considering the protein level in the mixes, the viscosity of ice cream mixes increase as the protein level decreases.

• As the protein level decrease, the fat globules size grow larger. The larger globules sizes causing high internal resistance, thus contributed to high viscosity (Schmidt & Smith, 1989).

Effect on the fat destabilization of ice cream.

NMS D50(µm) D90(µm)Ice cream

mixesIce cream Ice cream

mixesIce

creamSMR A 1.594 3.932 5.873 24.391SMR B 1.556 3.962 4.830 21.454

SMP 1.469 3.753 3.489 18.586

*presented values are the means of triplicates.*D50 is 50% volume cumulative diameter.*D90 is 90% volume cumulative diameter.

• The size of fat particles (D90) in frozen ice cream increases in the sequence of SMP< SMR B< SMR A.

• Higher D90 values of fat globules size in ice cream reflect that the fat globules tended to agglomerate or completely coalescence after the freezing process.

• This indicates that low protein level will resulted in formation of big fat particles in ice cream.

SMR A SMR B SMP0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

30.0%

35.0%

40.0%

45.0%

Different NMS

Agg

lom

erat

ion

ind

ex(%

)

Effect of skimmed milk powder replacers on fat destabilization of ice cream

• The results show that high protein level (SMP) encounter less fat destabilization compare to another two ice cream which are made from low protein level NMS.

• High protein level tends to produce a more stable emulsions with small fat particles sizes and the fat particles are well covered by sufficient amount of protein, thus reduced destabilization of fat from occurring during freezing process.

• Low level of protein content resulted in formation of unstable emulsion which will favor complete coalescence of fat globules in ice cream mixes (Goff, 1997).

• It is predicted that higher fat agglomeration index found in the ice cream mixes contain SMR A and SMR B is due to the complete coalescence of fat globules rather than partial coalescence.

• This results agree with the work done by Goff (1997) and Tcholakova et al. (2006).

Effect on the physical properties of frozen ice creams.

NMS Overrun (%)SMR A 69.4a

SMR B 76.7b

SMP 83.7c

*Presented values are the means of triplicate.*Values within a column not sharing a common letter (a, b, c, etc.) differ significantly, P < 0.05.

Effect of skimmed milk powder replacers on overrun of ice cream

• For ice cream with low protein level, complete coalescence occurred during the freezing process, thus fat globules fail to form a firm and interconnected structure which can trap the air inside without collapsed.

• According to Goff (1997), overrun increase as the protein increase to a certain level. Higher protein level in ice cream mixes lead to sufficient partial coalescence of fat globules. Small air bubbles were form and stabilize by the 3-D fat network and the protein.

SMRA SMR B SMP0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

NMS source

Res

ista

nce

to

pen

etra

tion

(N

)

Effect of skimmed milk powder replacers on hardness of ice cream

• This phenomenon can be explained by the overrun possessed by the ice cream itself.

• Wilbey et al. (1998) found an inverse relationship between overrun and hardness. Ice creams with high overrun are not able to resist high external forces.

• Goff et al. (1995) found that ice cream with higher overrun were more easily deformed under stress.

• Increasing level of protein in ice cream will result in increasing overrun and reduce the hardness of the ice cream.

0 10 20 30 40 50 60 70 80 900.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

SMR ASMR BSMP

Time(minutes)

Mas

s lo

ss(%

)

Effect of skimmed milk powder replacers on meltdown properties of ice cream

• The meltdown rate is said to be increase as the protein level in the ice cream decrease.

• This is due to the coalesce structure that form by unstable emulsion at low protein level.

• Overrun and fat destabilization are two of the factor that always being discussed.

• Increase of overrun will help to increase the heat resistance or prolong the meltdown time. This is because of the insulating effect of air inside the ice cream (Muse & Hartel, 2004).

• Theoretically, the higher degree of fat destabilization would favor better meltdown properties.

• However, our results do not agree with this relationship; because the degree of fat destabilization by fat agglomeration index do not show the nature of the fat destabilization occur in ice cream.

• The high destabilization in a stable emulsion is due to partial coalescence which will form mechanically strong foam by the large amount of interconnected fat crystals networks (Koxholt et al., 2001).

• Our studies are more towards formation of unstable emulsion (due to low protein level), the destabilization of fat globules in ice cream are more likely complete coalescence.

Chapter 5Conclusion

• Base on the results obtained, it can be conclude that homogenization pressure at 15/5Mpa is actually sufficient to produce a good quality palm oil based ice cream with acceptable physical properties.

• This prediction is based on the high overrun, small fat particles size, moderate fat destabilization, moderate hardness and moderate viscosity obtained.

• But, this prediction is yet to be proven by the sensory evaluation to examine the mouth feel and texture of the ice cream produce.

• Thus, further studies on effects of homogenization pressure on sensory properties of palm oil base ice cream are needed.

• This studies revealed that ratio of 1:1 replacement of skimmed milk powder by SMR A and SMR B are actually not favor the physical quality of palm oil based ice cream.

• Generally, decrease in protein level (less than optimum concentration) would increase the mix viscosity, fat particles size, hardness, fat destabilization and meltdown rate of palm oil ice cream.

• We realized that key factor affecting the physical properties is the stability of the emulsion form by different protein level in ice cream.

• Thus, further studies on emulsion stability and type of skimmed milk powder replacers is needed.