Ice-cream mixes

Pasteurization may be carried out by batch- or continuous-flow processes. In the batch process, each particle of milk must be heated to at least 63°C and held continuously at this temperature for at least 30 min. In the continuous process, milk is heated to at least 72°C for at least 15 s ia what is known as high temperature—short time (HTST) pasteurization, the primary method used for fluid milk. For milk products having a fat content above that of milk or that contain added sweeteners, 66°C is requited for the batch process and 75°C for the HTST process. For either method, foUowiag pasteurization the product should be cooled quickly to <7.2° C. Time—temperature relationships have been estabHshed for other products including ice cream mix, which is heated to 78°C for 15 s, and eggnog, which must be pasteurized at 69°C for 30 min or 80°C for 25 s. 

Sherbets have a low fat content (1—2%), low milk soHds (2—5%), and a sweet but tart flavor. Ice cream mix and water ice can be mixed to obtain a sherbet. The overmn in making sherbets is about 40—60%. 

Ice-cream is a product which has been developed since mechanical refrigeration became available. Ice-cream mixes comprise fats (not always dairy), milk protein, sugar and additives such as emulsifiers, stabilizers, colourings, together with extra items such as fruit, nuts, pieces of chocolate, etc., according to the particular type and flavour. The presence of this mixture of constituents means that the freezing... 

Ice cream is a frozen dessert prepared from dairy products and sugars with tremendous consumer acceptance. It is distributed and served in many forms and shapes. A typical formula for ice cream mix is ... 

Sodium carboxymethylcellulose (commonly known as CMC) was introduced in 1945 by Josephson and Dahle 10) for use in ice cream. It is cold water-soluble, will not react with acid, and has excellent water-binding properties. When properly processed, it is easily dispersible and quickly soluble in the mix. These properties make it well suited for high temperature-short time (HTST) mix. When used alone, it has a tendency to cause separation or wheying off in the mix. Irish moss extract is used with CMC to eliminate this condition. From 0.15 to 0.25% CMC is most often used in ice cream mix. 

Ice cream serves as a wonderful (and tasty) example of a complex, dynamically heterogeneous food system. A typical ice cream mix contains milk or cream (water, lactose, casein and whey proteins, lipids, vitamins, and minerals), sucrose, stabilizers and emulsifiers, and some type of flavor (e.g., vanilla). After the ingredients are combined, the mix is pasteurized and homogenized. Homogenization creates an oil-in-water emulsion, consisting of millions of tiny droplets of milk fat dispersed in the water phase, each surrounded by a layer of proteins and emulsifiers. The sucrose is dissolved in... 

Feijoo, S.C., Hayes, W.W., Watson, C.E., Martin, J.H. (1997). Effects of Microfluidizer technology on Bacillus licheniformis spores in ice cream mix. Journal of Dairy Science, 80,2184-2187. 

Vega, C., Goff, H.D. (2005). Phase separation in soft-serve ice cream mixes rheology and microstructure. International Dairy Journal, 15, 249-254. 

Cooling solutions to below their freezing point results in the formation of ice. If solutions of sugars are cooled rapidly, non-equilibrium ice formation occurs. This is the most common form of ice in frozen dairy products (e.g. ice-cream). Rapid freezing of ice-cream mixes results in the freeze concentration of lactose and other sugars, resulting in supersaturated solutions if the temperature is too low to permit crystallization. The rapid cooling of lactose results in the formation of a supersaturated, freeze-concentrated amorphous matrix. 

Frozen desserts made from sugar, water, fruit acid, color, fruit or fruit flavoring, and stabilizer, and containing a small amount of milk solids added in the form of skim milk, whole milk, condensed milk, or ice cream mix, are known as sherbets. Federal standards for these products are included in Table 2.7. 

Meyer, R. I. and Jokay, L. 1960. The effect of an oxygen scavenger packet, desiccant in package system on the stability of dry whole milk and dry ice cream mix. J. Dairy Sci. 43, 844. 

Some studies have been made on the effects of other sugars on the solubility of lactose (Nickerson and Moore 1972). At 10 to 18°C, a 14% sucrose solution, comparable to that in ice cream mix, reduces lactose solubility only slightly. However, the data in Table 6.3 show that concentrations of 40 to 70% sucrose reduce the solubility of lactose appreciably—to 40 to 80% of normal. At temperatures near 0°C, the solubility of lactose is reduced by about one-half by saturating the solution with sucrose. 

Ice cream is manufactured by rapidly freezing and simultaneously whipping an approximately equal volume of air into the formulated mix (Berger, 1976 Keeney and Kroger, 1974). Ice cream mix contains a minimum of 10% milk fat and 20% total milk solids, except when chocolate, fruit or nuts, are added. In addition to milk solids, ice cream mix normally contains 10-15% sucrose, 5-7% corn sweetener, 0.2-0.3% stabilizer gum, <0.1% emulsifier, and small amounts of natural or artificial color and flavor ingredients. 

Ice cream is made front skimmed milk, condensed skimmed milk or skimmed milk powder in combination, and dairy cream, butter or butter oil. In some countries vegetable fat is used to replace dairy fat. Usually, monoglycerides or mono-diglycerides are used, but other more polar emulsifiers can also be used. The emulsifier dosage is similar to that used in imitation cream. Ice cream also contains sugar and hydrocolloids, which mainly influence the freezing behaviour of the ice cream mix. 

Figure 1 Melting enthalpy of bulk fat and emulsified fat of ice cream mix with (+E) and without (-E) emulsifier after cooling at 5°C measured by DSC.

The time scale of fat crystallization is much shorter for topping powders than for ice cream mix as presented in Figure 2. This is due to the much higher emulsifier content in topping powder. The induction of fat crystallization in whippable emulsion systems is due to interfacial protein desorption from the fat globules of the emulsion mediated by the emulsifiers. This phenomenon is described in section 3.1. 

The FFE method is of great practical use to verify the level of mechanical treatment applied to ice cream mix during aeration and freezing. It also provides an indication of the storage stability and creaminess of the product tested27. 

In whippable emulsions, such as ice cream mix, toppings and homogenized creams, weakening the protein-fat binding by emulsifiers results in an improvement of the whipping properties9 12-33,34. 

Figure 11 Protein binding to fat globules in ice cream mix at various temperatures and after ice cream production (I.C.). The latter analyzed at 5°C after thawing ice cream at 0°C. Effect of hydrocolioid blend and emulsifier.

The desorption of thick protein layers from fat globules of ice cream mix containing emulsifiers and hydrocolloids during ageing and mechanical treatment may also be observed by transmission electron microscopy (Figure 12). The protein bound to the surface of fat globules is desorbed as a tiiick coherent skin23. 

The ageing at 5°C of whippable emulsions such as ice cream mix will enhance the hydration of milk proteins in the system. This is due to a property of casein micelles in milk. At low temperatures, the hydration or voluminosity of casein increases. The voluminosity is the volume of hydrated protein per gram of protein. This can be studied by analyzing the protein and water content in the sedimented casein pellet after centrifugation of skimmed milk. 

During ageing of the mix, interfacial milk protein hydration also increases simultaneously with protein desorption from the fat globules. The water content of the isolated cream layers after centrifugation of ice cream mix can be analyzed by Karl Fischer titration. From such analyses, interfacial protein hydration can be calculated (Figure 13). 

Figure 13 Desorption and hydration of protein bound to fat globules of ice cream mix during ageing at 5°C.

Figure 15 Effect of temperature on average particle size of ice cream mix with and without emulsifier.

The increased interfacial hydration in the presence of emulsifiers gives rise to a slight increase in the particle size of the fat globules in the ice cream mix (Figure 15). The volume of cream layers after centrifugation also increases up to 100% when lowering the temperature... 

Emulsifiers were dissolved in sunflower oil, and protein in the water phase. With increasing amounts of saturated mono-digiycerides in the oil phase, increased interfacial activity was observed at low temperatures. At a concentration of 0.1%, which is usual in ice cream mix, the drop in interfacial tension starts just below room temperature (15°C). At this concentration no visible crystallization of emulsifier takes place in the oil phase. 

Figure 19 Recommended dosages of commercial integrated emulsifier/hydrocolloid blend (CREMODAN SE 47) in ice cream mix.

The adsorption of emuisifier to the air-water interface can be detected clearly by surface tension measurements because emulsifiers result in far greater depression of surface tension than proteins. Such analyses may also give information regarding the binding mechanisms of emulsifier in low-fat ice cream mix described below. 

Monoglycerides and mono-diglycerides have low HLB values and cannot form micelles. They build up a multi-layer at the surface, resulting in a constantly decreasing surface tension as their concentration increases. However, in systems with proteins such as fat-free ice cream mixes, these emulsifiers behave as if they have a CMC. A possible explanation for this observation is that the unbound emulsifier in the fat-free mix is in equilibrium with the protein-bound emulsifier. Above a certain concentration of emulsifier in the mix, any surplus of emulsifier will adhere to the protein in the water phase after the surface has been saturated. The unadsorbed emulsifier is seen as very small crystals less than 200 nm by electron microscopy analysis4. ... 

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