Emulsifier Technology In Foods

Most foods consumed by humans are emulsions, in that they contain either fats or oils dispersed in an aqueous phase, or they contain an aqueous phase dispersed in a fat or oil. An example of the prior emulsion would be milk; an example of the latter would be butter.

A food emulsion may be described as a multiple-phase system that contains at least two components that are normally immiscible. Oil and water are examples of such incompatible components. The water or aqueous phase may contain many other ingredients that are truly soluble in the aqueous phase such as sugars and salts. It may also contain colloidally dispersed components such as proteins and carbohydrate polymers such as cellulose. The fat or oil phase may contain other lipids such as phospholipids and glycolipids, and certain vitamins, colors, and sterols.

The preparation by humans of food emulsions not found in nature has been considered a culinary art and has been practiced as an art for centuries. A perfect example of an artful culinary emulsion has been mayonnaise. Such emulsions did not require long-term stability because they were consumed within a short period of time in the home or restaurant. Such problems as freeze/thaw stability, long-term storage, the physical rigors of transportation, and high degree of aeration did not concern the chef of bygone eras. His emulsions would be considered crude by today's standards. His emulsion—a sauce, for example—would be acceptable if stable for only a few hours, as compared with the months of stability required today in commercially produced emulsions such as salad dressings.

Milk and salad dressings are two of the primary examples of one type of emulsion—the oil-in-water emulsion. The oil or lipid phase is also known as the disperse, discontinuous, or internal phase. It is dispersed in the aqueous serum phase, also known as the external or continuous phase.

Butter and margarine are obvious examples of the opposite type of emulsion, the water-in-oil emulsion. The aqueous phase is dispersed in the fat or oil and is now known as the discontinuous or internal phase, as the lipid has become the continuous or external phase.

A gaseous phase can also exist and may be external, as in the case of an aerosol, or internal, as in whipped topping. Dual emulsions are commonly encountered; a cake batter is a good example of the latter. Air or leavening gasses are dispersed in the fat, which is, in turn, dispersed in the aqueous phase of the oil-in-water cake batter.

The viscosity of a food emulsion is a function primarily of the external phase. It is generally lower when the external phase is aqueous, as in the case of milk, and higher when the external phase is lipid, as in the case of margarine. Several other factors can affect emulsion viscosity. In the case of an oil-in-water type of emulsion, packing or clumping of the internal phase can affect yield value and viscosity. An example of such an emulsion is mayonnaise. The internal dispersed phase (oil) occupies over 70% of its volume, closely approaching its theoretical maximum when the oil globules are of uniform spherical shape. Such an emulsion exhibits little or no flow properties, and its yield value and viscosity are such as to lead the causal observer to assume it may be a water-in-oil emulsion.

Oil-in-water emulsions can contain higher than theoretical limits of lipid internal phase (74%) if globules are misshapen due to compression, and viscosity can be further affected by hydrogen bonding and van der Waals forces. Surface charges supplied by components such as phospholipids can reduce viscosity by imparting repel-lency.

When the internal phase of an oil-in-water emulsion is low, as in the case of dairy products, ingredients such as colloids, including cellulose, starch, and algins, may be added to increase viscosity. Homogenization of the lipid phase to attain more surface area per unit weight of disperse phase will increase viscosity. Indeed, when homogenization of dairy foods was introduced in the United States in the 1930s, it so improved perceived richness due to increased surface area and resultant viscosity that an attempt was made to ban the process on the basis that it deceived the consumer. As an example, using typical homogenization procedures, milk with an average 8 // fat globule is converted to 512 globules of 1 /i providing an eightfold increase in surface area.

Most commercial food emulsions contain the disperse phase in small globules in the range of 0.1 to 0.2 ¡i. With water-in-oil emulsions such as margarine, the viscosity, or plasticity, is a function primarily of the crystalline solids contribution of the fat, as well as its melting point.

The aqueous phase included in the margarine lipid phase is dispersed using a scraped surface crystallizer, such as the votator, so that the water particles are as small as possible. Large particles explode into steam when the margarine is used for cooking with such violence as to cause spattering. A properly manufactured margarine will have the dispersed water particles in the 1 to 5 ju range.

Most oil-in-water emulsions such as dairy-type frozen desserts, because of very efficient modern homogenizers, possess fat globules with a diameter of less than 0.5 The size of the fat globule will affect the light reflected to the viewers eyes in a simple oil in water emulsion. In fact, the size of the oil globule can be estimated from the appearance of the emulsion as given in Table 1.

The physical stability of an emulsion, that is, the tendency of the two phases not to separate, takes place in accordance with Stokes Law:

Homemade Pet Food Secrets

Homemade Pet Food Secrets

It is a well known fact that homemade food is always a healthier option for pets when compared to the market packed food. The increasing hazards to the health of the pets have made pet owners stick to containment of commercial pet food. The basic fundamentals of health for human beings are applicable for pets also.

Get My Free Ebook

Post a comment