Make foams and emulsions stable.

To satisfy consumer needs for better quality, the food industry needs to develop rational approaches for modifying processes. It must identify targets for enhancing the value of raw materials. Efforts at the U.K.'s Institute of Food Research (IFR) are focusing on these objectives. The results are showing us how to improve the taste, texture, aroma, appearance and shelf life of foods.

For example, the creation of foams and emulsions requires the generation of stable air-water and oil-water interfaces. A major obstacle technologists have faced is the complex interplay between proteins and lipid-like molecules present at the interface. Microscopic technology has allowed IFR researchers to visualize the network structures formed by proteins at interfaces. Scientists have been able to see the mechanisms by which lipids attack and disrupt these structures, leading to the instability of foams and emulsions. Such generic models make it possible to analyze complex foods.

In bread, a thin aqueous film stabilizes the gas cells and provides the desired foam structure of the loaf. Institute scientists have isolated the components of this aqueous phase (dough liquor). They have shown that the surface activity of this material is related to gas cell size.

Visualizing dough liquors at air-water interfaces reveals an unstable protein-lipid system. In commercial baking, adding DATEM esters to control stability appears to completely displace the protein, resulting in a lipid-stabilized foam.

DATEMs (diacetyl tartrate esters of monoglycerides) are emulsifiers. They appear to be very effective at stabilizing the foam structure in bread dough. They prevent collapse, particularly during the later stages of proofing and the early stages of baking. Their mode of action and their interaction with proteins and lipids are not clear.

An alternative to adding DATEM esters would be to enhance naturally occurring surface-active proteins, or to suppress the lipids present, leading to protein-stabilized gas cells. Proteomic techniques are being used to identify such proteins as targets for improved wheat varieties that could be used in bread-making.

The main focus of research is the mechanism underlying the structures formed in complex food systems, such as in ice cream and whipped cream. In these applications, the emulsion helps to stabilize the foam and generate the unique structure and texture found in these products. The phase state of the fat is very important here. If the fat is in the liquid state, then no stabilization of the foam occurs. So a certain amount of solid fat is required to form a solid network which stabilizes and supports the foam structure.

Another area of interest involves understanding the molecular basis for shelf life and stability. Scientists want to know how proteins, emulsifiers and other ingredients stabilize foams and emulsions and the effect of processing on the structure of proteins. The scientists also want to understand the ability to stabilize a foam or emulsion.

Other processes of particular interest are dynamic changes in these systems, such as flocculation and aggregation. These processes can completely change the appearance, texture and taste of an emulsion, and can even prolong shelf life. The specific changes occurring over time are again not clear, but how the emulsion droplets interact and form structures within the emulsion can be extremely important.

Further information. Peter Wilde, Institute of Food Research, Norwich, NR4 7UA, U.K.; phone: [phone]; fax: [phone]; email: [e-mail].