A modified ice cream processing routine that promotes fat destabilization in the absence of added emulsifier

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1 International Dairy Journal () 13 1 A modified ice cream processing routine that promotes fat destabilization in the absence of added emulsifier K.I. Segall, H.D. Goff* Department of Food Science, University of Guelph, Guelph, Ontario, Canada N1G W1 Received 1 February ; accepted July Abstract The quality of ice cream made without added emulsifier using a modified processing routine was compared to ice cream made conventionally with and without added emulsifier. Two-phase process ice cream was created by preparing two separate phases; emulsion (fat, some protein, water) and solution (remaining protein, sugar, corn syrup solids, stabilizer, water) and combining them just before freezing. Quality indicators included percent fat destabilized, overrun and meltdown rate. Conventional process ice cream containing emulsifier exhibited a high degree of fat destabilization, high overrun and slow meltdown. Ice cream produced conventionally without emulsifier underwent little fat destabilization, had low overrun and melted rapidly. Ice cream produced by the two-phase process showed good fat destabilization and slow meltdown with moderate overrun, suggesting this method was successful in promoting desirable structure formation without added emulsifier. r Elsevier Science Ltd. All rights reserved. Keywords: Ice cream emulsion; Fat destabilization; Overrun; Emulsifiers 1. Introduction The ingredients and processing steps required to produce good quality ice cream are well known and employed worldwide. Ice cream mix formulations vary but a conventional mix typically contains a fat source, a protein source, and other functional ingredients including sweeteners, stabilizers and emulsifiers (Marshall & Arbuckle, 199). Ice cream processing involves blending all of the ingredients together and then pasteurizing, homogenizing, aging and freezing the mix. Several of these processing steps contribute to fat structure development in ice cream (Goff, 1997a). Homogenization of the hot mix converts the bulk fat into finely divided droplets. Aging allows time for fat crystallization and also rearrangement of the surfactant membrane. During the freezing step the mix is aerated and the individual fat globules are partially coalesced into a three-dimensional network (Berger, 1997; Goff, 1997a; Thomas, 191). The presence of some fat crystals is critical for fat structure development as protruding *Corresponding author. Tel.: x37; fax: address: dgoff@uoguelph.ca (H.D. Goff). crystals may initiate the interaction between droplets thus helping to hold flocculated fat together (van Boekel & Walstra, 191). Ice cream mix contains an excess of protein compared to that required to cover the surface area of the fat droplets created by homogenization. As a result, the newly created droplets are surrounded by a saturated and thick coating of adsorbed protein, including bulky casein micelles (Pelan, Watts, Campbell, & Lips, 1997). This layer of adsorbed protein prevents the close association of droplets necessary for partial coalescence to occur as evidenced by the low levels of destabilized fat found in ice creams formulated without added emulsifier (Barfod, Krog, Larsen, & Buchheim, 1991; Goff & Jordan, 199). During the aging step the emulsifiers, which are thermodynamically better surfactants than proteins, migrate from the serum to the interface and displace proteins. This produces a thinner, more fragile membrane on the droplets and allows partial coalescence and fat structure development to occur (Barfod et al., 1991; Goff & Jordan, 199). Therefore, the presence of emulsifier in the formulation is considered necessary to produce ice cream with desirable body. Previous studies have begun to explore the possibility of producing acceptable ice cream without the use of an 95-9//$ - see front matter r Elsevier Science Ltd. All rights reserved. PII: S 95-9()117-

2 K.I. Segall, H.D. Goff / International Dairy Journal () 13 1 added emulsifier (Segall & Goff, 1999, ). Production of such an ice cream could involve a modified processing routine with two separate ingredient streams prepared and combined just before freezing (Mussellwhite & Walker, 1971). Controlling the protein surface concentration on the mix emulsion droplets by restricting the amount and type of protein available upon homogenization has been shown to allow the formation of an emulsion that is quiescently stable but also undergoes partial coalescence when sheared (Segall & Goff, 1999). Ice cream could be produced by combining this fragile, low protein surface concentration emulsion phase (containing all the fat and a fraction of the protein and water) with a solution of the remaining ingredients (termed the solution phase) just before freezing (Fig. 1). Inclusion of carrageenan in the solution phase would limit protein migration from the serum to the interface and allow a desirable amount of partial coalescence after combination of the two phases (Segall & Goff, ). In this study, pilot scale ice cream manufacturing techniques were used to prepare ice cream according to the two-phase process concept and the quality of the product as related to fat structure was compared to ice cream made in the conventional way. Emulsion butteroil whey protein isolate water Pasteurization Homogenization Aging Freezing Ice Cream Serum skim milk powder sucrose corn syrup solids stabilizer, water Pasteurization Fig. 1. Flow chart illustrating the steps of the two-phase ice cream making process.. Materials and methods.1. Ingredients All ice cream mixes were formulated to contain % w/w butteroil (Gay-Lea Foods, Teeswater, Ont.), % protein, % sucrose (Lantic Sugar, Toronto, Ont.), 5% corn syrup solids (3 D.E., Casco Inc., Toronto, Ont.) and.1% guar (Germantown Canada Inc., Scarborough, Ont.). Ice creams made by the conventional process derived all their protein from skim milk powder (11%, 3% protein, Gay-Lea Foods, Guelph, Ont.) and were also formulated with and without.15% emulsifier blend (% mono and di-glycerides, of which % was mono, I.V.o3 and % polysorbate. Germantown Canada Inc., Scarborough, Ont.). The conventional mix without the emulsifier blend was also formulated with and without.% k-carrageenan (Germantown Canada Inc., Scarborough, Ont.). Ice creams made by the two-phase process were formulated as separate emulsion and solution phases. The emulsion phase was created from butteroil (5%), whey protein (.3%) supplied by a from whey protein isolate (93% protein, Protose Separations, Teeswater, Ont., Segall & Goff, 1999), and water. This emulsion was combined with a solution of 17.% skim milk powder, % sucrose,.33% corn syrup solids,.17% guar and.7% carrageenan in water, in the ratio % solution phase to % emulsion phase, giving a formulation with proportions identical to that used in the conventional process... Ice cream production For the conventional ice cream making process all ingredients were blended and then pasteurized in a double boiler pot at 51C for 3 min. The mixes were then immediately homogenized with a Gaulin V15- T (APV Gaulin, Everett, MA) two stage single piston homogenizer with 17. MPa pressure on the first stage and 3. MPa on the second. Mixes were promptly cooled and then aged overnight at 1C. The next day the mixes were flavoured with vanilla (1%) and L of mix was frozen in a pre-chilled Taylor B733-3 batch freezer (Techni-Craft, Rockton, IL). The freezer was run under whipping and cooling conditions until the temperature of the product was lowered to the desired draw temperature ( 51C). Once this temperature was reached the refrigeration was turned off and agitation of the mix continued until the total time in the freezer reached 15 min. Every.5 min a sample was removed from the barrel for particle size and destabilized fat analysis. Once the endpoint was reached the overrun in the ice cream was measured and the ice cream was packaged and hardened at 351C.

3 K.I. Segall, H.D. Goff / International Dairy Journal () Production of the two-phase process ice cream was similar. After dissolution of the dry ingredients, both the emulsion phase and the solution phase were pasteurized at 51C for 3 min. However, only the emulsion phase was homogenized (same conditions as above). Both phases were then cooled and aged overnight at 1C. The solution and emulsion phases were combined immediately prior to freezing in the ratio of % solution phase to % emulsion phase and the mix flavoured with vanilla (1%) and frozen as above. Sampling and analysis of the ice cream proceeded as with the conventional process ice cream. All ice creams were manufactured and analysed in triplicate..3. Analyses Particle size distributions of the mix and melted ice cream samples were determined by integrated light scattering using a Mastersizer X (Malvern Instruments Ltd., Malvern, UK) running manufacturers presentation code 33 (corresponding to a sample refractive index of 1.1 and sample absorbance of.1). Measurements were performed at room temperature and dilution in the sample chamber was approximately 1:. Overruns in the ice creams were calculated by comparing the weight of a known volume of ice cream to the weight of the same volume of unfrozen ice cream mix. The fat destabilization index in the melted ice cream samples was determined by a method based on the procedure of Goff and Jordan (199). Small samples of melted ice cream (3 g) were diluted to 3 g with water in a 5 ml flask. A 1 ml sample of this solution was then diluted to 5 ml in a volumetric flask giving a total dilution of 1:5. The diluted solution was allowed to stand for 5 min and then the absorbance of the solution at 5 nm was measured. Turbidity was used as the indicator of the amount of destabilized fat in the sample by applying the following equation: Fat destabilization index ¼ðA ½ 5 ðdiluted mixþ A 5 ðdiluted meltþþ A 5 ðdiluted mixþš: ð1þ Meltdown tests were conducted on hardened ice creams that were previously tempered to 11C overnight. Approximately 5 g brick shaped samples (width= cm, depth= cm, height= cm) of ice cream were suspended on a wire mesh ( holes/.5 cm, wire thickness=.9 mm) and allowed to melt in room temperature air. The material that melted and drained through the wire mesh was collected and weighed every min. A plot was constructed of % mass loss versus melting time. This plot was sigmoidal in shape with a linear region of maximal melting rate. The % mass loss per minute in this linear region was used to compare the meltdown rates of the different samples... Statistics All statistical analyses were performed on a personal computer running SAS for windows v.. (SAS Institute Inc., Cary, NC). Analysis of variance was performed using the routine Proc ANOVA and multiple comparisons of means were conducted using a Bonferroni t test. 3. Results and discussion Ice creams were produced by the conventional process with and without added emulsifier to provide extremes of product quality to which the two-phase product could be compared. As would be expected, production of ice cream by the conventional method with included emulsifiers in the formulation yielded an excellent product. This ice cream contained a high percentage of destabilized fat with the formation of large fat aggregates as the freezing process progressed (Fig. ). Other favourable properties of this ice cream, associated with the amount of destabilized fat, were the high overrun and slow meltdown rate (Table 1). The destabilized fat provides a structure throughout the serum phase and at the air interface, stabilizing the air cells and trapping the aqueous phase of the ice cream, preventing its drainage upon meltdown (Goff, 1997b; Goff, Verespej, & Smith, 1999). The ice cream processed in the conventional manner but without emulsifier in the formulation contained a much lower level of destabilized fat than in the presence of emulsifier and there was also a much smaller increase in average particle size with freezing time (Fig. ). The lack of fat destabilization in the system without emulsifier was likely due to the heavy coating of protein on the fat globules preventing close association and partial coalescence of the droplets. Overrun was very low for this product and the meltdown rate was very high (Table 1) as there was little fat network to stabilize the air cells or constrain the draining serum. Carrageenan has been shown to be effective at inhibiting the migration of milk proteins from solution to an oil water emulsion interface (Segall & Goff, ). Therefore, carrageenan was incorporated into the mix containing no emulsifier to see if the polysaccharide could introduce some of the favourable properties normally attributed to emulsifier. The properties of the ice cream produced with or without carrageenan were similar. Ice cream containing carrageenan showed no difference in fat destabilization, average particle size (Fig. ), overrun or meltdown rate (Table 1) compared to the ice cream produced without carrageenan. Any effect on meltdown would be likely due to the effect of the polysaccharide on the viscosity of the melting serum rather than a fat based effect.

4 1 K.I. Segall, H.D. Goff / International Dairy Journal () Fat destabilization index (%) Mean particle diameter (µm) Time in freezer (min) 5 15 Time in freezer (min) Fig.. Changes in: amount of destabilized fat, and volume weighted mean particle diameter d ;3 with time in freezer for conventionally processed ice creams ((), emulsifier, no carrageenan; ( ), no emulsifier, no carrageenan; (m), no emulsifier, carrageenan) and ice cream prepared by the two-phase process (.). Error bars represent standard error. Table 1 Influence of ice cream formulation and processing on product overrun and meltdown rates. See text for a description of conventional and two phase mix processing Process Added emulsifier Carrageenan Overrun (%) Meltdown rate (% mass loss min 1 ) Conventional Yes No 9 a.3 b Conventional No No c.99 a Conventional No Yes 53 c.7 b,a Two phase No Yes 7 b.35 b Values designated with different letters are significantly different ðpo:5þ: Production of ice cream by the two-phase process yielded a product with properties that differed somewhat from ice cream produced from the conventional mix with emulsifier. The amount of fat destabilized at the end of the freezing process was similar for both ice creams but the rate of partial coalescence differed (Fig. ). The size of the generated fat aggregates appeared smaller in the two-phase ice cream compared to the conventional emulsified product (Fig. ). The two-phase product did not aerate as well as the conventional emulsified ice cream with an average percent overrun being significantly lower ðpo:5; Table 1). Inhibition of protein movement through interaction with carrageenan, while desirable in keeping the protein off the oil water interface, may have prevented the proteins from stabilizing the initial air water interface. As well, the conventional emulsified mix contained saturated mono-glycerides which exhibit air cell stabilizing effects independent of fat destabilization (Pelan et al., 1997; Turan, Kirkland, Trusty, & Campbell, 1999). It should be noted however that the overrun obtained with the two-phase process was still significantly higher ðpo:5þ than the overrun achieved by the conventional process in the absence of emulsifier. The meltdown rates for the two-phase process ice cream and the conventional product were not significantly different. Overall it appeared that the two-phase process produced good fat destabilization but resulted in slightly lower ability to hold air. However, it must be kept in mind that these experiments were conducted using a batch freezer. Continuous freezers offer more control and may be more effectively used to aerate an ice cream. Other ingredients such as sodium caseinate could also be introduced to increase the overrun (Goff, Kinsella, & Jordan, 199). Following the particle size distributions over time suggests that the different types of ice cream mixes used in this study may have undergone destabilization in different ways when frozen. The conventional ice cream mix with emulsifier shows a monomodal distribution prior to any freezing (Fig. 3a). As this mix was frozen the original peak decreased in size corresponding to the growth of a second peak (Fig. 3b) indicating the presence of particles of large size (> mm). The conventional mix formulated without emulsifier also had a monomodal distribution prior to freezing (Fig. a). In the later stages of the freezing process a small amount of fat destabilization occurred as shown by the appearance of a shoulder on the original peak (Fig. b). The process of destabilization in the ice cream made by two-phase processing appeared to occur by a combination of the effects mentioned above. The particle size distribution for the mix was essentially monomodal (Fig. 5a) although there was a small tail on

5 K.I. Segall, H.D. Goff / International Dairy Journal () Frequency (%) Fig. 3. Particle size distributions for conventionally processed ice cream containing emulsifier: mix; after 15 min in freezer. Error bars represent standard error. 1 1 Frequency (%) Fig.. Particle size distributions for conventionally processed ice cream without emulsifier: mix; after 15 min in freezer. Error bars represent standard error. 1 1 Frequency (%) Fig. 5. Particle size distributions for ice creams prepared by the two-phase method: mix; after 15 min in freezer. Error bars represent standard error. the distributions likely due to a carrageenan induced clustering of casein micelles seen in the serum phase. As this mix was frozen, large particles were formed and a shoulder also developed on the original peak (Fig. 5b). The number of large particles in this ice cream was lower than observed for the conventional emulsified mix. Therefore, it appeared that protein deficient, emulsifier coated membranes and protein coated membranes destabilize in different ways. The membranes coated with added emulsifier likely offered more surfaces on which fat globule interaction could occur i.e. collision between two droplets during the dynamic freezing

6 1 K.I. Segall, H.D. Goff / International Dairy Journal () 13 1 process was much more likely to lead to complex formation. This would allow the rapid growth of large fat structures. If the droplets were coated with bulky protein molecules it would be much less likely that collision of droplets would occur in such a way that the droplets were able to partially coalesce. When the mix was frozen there was a slight increase in the average size of the droplets but there was negligible large complex formation. Fat network formation in the ice cream made by the twophase process reflects characteristics of both the emulsified and non-emulsified mixes. The low protein surface concentration on the droplets seemed to allow the formation of some large fat complexes but there was still some restriction on the interaction of the fat globules as evidenced by the shoulder that appeared on the original peak.. Conclusions The two-phase ice cream making process has been successfully employed to produce an acceptable ice cream with no added emulsifier that behaved similarly to a conventional emulsified product, giving a significant improvement over ice cream made by the conventional process without emulsifier. Although the two-phase ice cream was successful from the standpoint of fat structure development, partial coalescence and the associated properties of the ice cream, many questions remain before this process could be of commercial value. Other properties of the ice cream not related to fat have yet to be considered, e.g. ice crystal size distribution and the susceptibility of the product to recrystallization. The two-phase process does offer a marketing advantage in that the product could be considered all natural. However, the novel processing steps may make the two-phase process cost prohibitive compared to the use of egg yolk components as the emulsifier and conventional processing steps for making natural ice cream. Acknowledgements The support of Good Humour Breyer s Canada Inc. and the Natural Sciences and Engineering Research Council of Canada is greatly appreciated. References Barfod, N. M., Krog, N., Larsen, G., & Buchheim, W. (1991). Effects of emulsifiers on protein fat interaction in ice cream mix during ageing I: Quantitative analyses. Fat Science and Technology, 93, 9. Berger, K. G. (1997). Ice cream. In S. E. Friberg, & K. Larsson (Eds.), Food emulsions (3rd ed.) (pp. 13 9). New York: Marcel Dekker. Goff, H. D. (1997a). Colloidal aspects of ice cream: A review. International Dairy Journal, 7, Goff, H. D. (1997b). Instability and partial coalescence in whippable dairy emulsions. Journal of Dairy Science,, 3. Goff, H. D., & Jordan, W. K. (199). Action of emulsifiers in promoting fat destabilization during the manufacture of ice cream. Journal of Dairy Science, 7, 1 9. Goff, H. D., Kinsella, J. E., & Jordan, W. K. (199). Influence of various milk protein isolates on ice cream emulsion stability. Journal of Dairy Science, 7, Goff, H. D., Verespej, E., & Smith, A. K. (1999). A study of fat and air structures in ice cream. International Dairy Journal, 9, Marshall, R. T., & Arbuckle, W. S. (199). Ice cream (5th ed.). New York: Chapman & Hall. Mussellwhite, P. R., & Walker, D. A. (1971). The effect of the colloidal state of the emulsion on ice cream structure. Journal of Texture Studies,, Pelan, B. M. C., Watts, K. M., Campbell, I. J., & Lips, A. (1997). The stability of aerated milk protein emulsions in the presence of small molecule surfactants. Journal of Dairy Science,, Segall, K. I., & Goff, H. D. (1999). Influence of adsorbed milk protein type and surface concentration on the quiescent and shear stability of butteroil emulsions. International Dairy Journal, 9, Segall, K. I., & Goff, H. D. (). Secondary adsorption of milk proteins from the serum to the interface in dairy emulsions: Effect on emulsion properties and possible means of reduction. International Dairy Journal,, Thomas, E. L. (191). Structure and properties of ice cream emulsions. Food Technology, 35(1), 1. Turan, S., Kirkland, M., Trusty, P. A., & Campbell, I. (1999). Ingredient interaction. Dairy Industries International,, van Boekel, M. A. J. S., & Walstra, P. (191). Stability of oil-in-water emulsions with crystals in the disperse phase. Colloids and Surfaces, 3, 9 11.