Milk fat as an emulsion

Milk contains 15 x 10 globules ml with a total interfacial area of 1.2-2.5 per g fat. 

Example. Assume a fat content of 4.0%, w/v, with a mean globule diameter of 3 m. 

---

Over 95% of the lipids in cows milk are present in the milk fat globules and most of the phospholipids are contained in the globule membrane, where they constitute about 30% of the total lipids present in the latter. The phospholipids are believed to act as an emulsion stabiliser and prevent coalescence of the globules. 

Finally, we should not forget to mention nature s own emulsions and foams. Examples of natural emulsions are rubber latex produced by Hevea brasiliensis, fat droplets in milk stabilized by proteins, fats from the diet emulsified in the duodenum and stabilized by bile acids and salts, and blood too may be regarded as an emulsion. Where (micro)organisms living in an aqueous environment produce gaseous metabolites, foams are often formed. This may be desirable, as in beer, or undesirable as in installations for the treatment of wastewater. 

Anhydrous Milk Fat. One high milk-fat material is butter oil (99.7% fat), also called anhydrous milk fat or anhydrous butter oil if less than 0.2% moisture is present. Although the terms are used iaterchangeably, anhydrous butter oil is made from butter and anhydrous milk fat is made from whole milk. For milk and cream there is an emulsion of fat-ia-semm, for butter oil and anhydrous milk fat there is an emulsion of semm-ia-fat, such as with butter. It is easier to remove moisture ia the final stages to make anhydrous milk fat with the semm-ia-fat emulsion. 

Butter. In the United States about 10 wt % of edible fats used are butter. Butter is defined as a product that contains 80% milk fat with not more than 16% moisture. It is made of cream with 25—40% milk fat. The process is primarily a mechanical one in which the cream, an emulsion of fat-in-semm, is changed to butter, an emulsion of semm-in-fat. The process is accompHshed by churning or by a continuous operation with automatic controls. Some physical properties are given in Table 16 (see Emulsions). 

We have already seen how milk is an emulsion comprising oil as a dispersion medium in a water-based dispersion medium. Milk fats also form colloids. The aqueous component of milk contains many vitamins, especially the salts of calcium, which baby mammals need to produce strong teeth and bones. 

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... 

There are a large number of industrial processes which employ cavitation as an energy source for the generation of fine emulsions and dispersions. One of the earliest devices which was developed for this purpose was the so-called liquid whistle (see Chapter 7) and this continues to be used widely. Typical examples of the uses of such whistles include the preparation of emulsion bases for soups, sauces or gravies which consist of a premix of water, milk powder, edible oil and fat together with flour or starch... 

Phospholipids. The phospholipids comprise approximately 1 % of the total lipid in bovine milk (ca.0.3 to 0.4 g/liter). While quantitatively minor, the ability of the phospholipids to form stable colloidal suspensions or emulsions in aqueous solution cause them to be important in the formation and secretion of milk fat. (Long and Patton 1978 Patton and Keenan 1975). Their physical properties as bipolar molecules and their relatively high concentration of unsaturated fatty acids also make them an important factor to consider during the storage and... 

Cream is the fat-rich portion of milk that is separated by skimming and contains at least about 18-20% fat (still in the form of an O/W emulsion). As the fat content increases from skimmed milk through thick creams, the solids-not-fat content decreases as illustrated in Figure 13.2 [826]. The viscosities of milk and cream depend on the concentrations of both fat and solids-not-fat as shown in the following empirical equation [215] ... 

Daily articles of life Milk is an emulsion of fat dispersed in water stabilised by casein and as all know is practically a complete food. Ice cream, is an emulsion, in which ice particles are dispersed in cream, stabilised by gelatin. Artificial beverages, coffee, fruit jellies are all emulsions in nature. The cleansing action of ordinary soap is due to a large extent on the production of OAV emulsion. 

Emulsions are not a human invention. In living nature they play an especially important role in the absorption of fats with nutrients. The earliest known use of an emulsion by humans is certainly the exploitation of milk and milk products such as cream, butter and cheese for nutritional purposes. With increasing prosperity the advanced civilisations of... 

Milk replacer fat emulsion. One important application of lecithin in animal feeds is as an emulsifier (314). As an example, milk replacer fat is emulsified to improve product wetting and dispersion upon mixing, to help minimize fat separation (i.e., emulsion stability), and to significantly reduce fat particle size, allowing improved fat digestibility. As an emulsifier in milk replacers, lecithin is used at 3-12% of the added fat. The type of lecithin used is affected by factors such as fat type, protein type, and the presence of stabilizers. 

Another parameter that influences the overall properties of the bulk emulsion is the physical state of the lipid droplets in an emulsion (17, 19, 28-31). Crystallization of lipid droplets in emulsions can be either beneficial or detrimental to product quality. Margarine and butter, the most common water-in-oil emulsions in the food industry, are prepared by a controlled destabilization of oil-in-water emulsions containing partly crystalline droplets. The stability of dairy cream to mechanical agitation and temperature cycling depends on the nature and extent of crystallization in milk-fat globules. It should be noted that because the density of the phases can change as crystallization occurs, the rate at which milkfat droplets cream can be altered as droplets solidify. Emulsion manufacturers should therefore understand which factors influence the crystallization and melting of emulsified substances, and be aware of the effect that droplet phase transitions can have on the properties of emulsions. 

---