Proteins are being used as ingredients in man-made food products because they contribute to one or more of the desired characteristics of that product. These characteristics might be consumer related, relating to texture, mouth feel, appearance or taste, or they could be

technology related, which includes both storage – shelf-life and palatability - and processing, such as mixing behaviour, foam, emulsion or gel formation.

 

Proteins contribute to one or more of these characteristics because of their functional properties - physicochemical properties that govern the performance and behaviour of a protein in food systems during preparation, processing, storage and consumption.¹

 

 

Performance factors

It is the exact composition, spatial structure and size that determine how proteins “act” in food products, thus how they function. Extrinsic factors such as pH and temperature; the presence of other constituents, such as salts, surfactants, gums, water and more; and process treatments all can alter the performance. Therefore, the functionality of a protein is largely affected by circumstances. The behaviour in model systems can be different from that in real food products. There are many reasons for these discrepancies.

 

• The interactions of the proteins with other components in the food product.

• The use of water by other components, so less water is available for the protein.

• Usually mixtures of proteins are being used. Most industrial protein preparations derived from a particular source, such as soy, egg or milk, are mixtures of different types. Furthermore, in food different protein sources are often intentionally mixed, mostly for nutritious or economic reasons.²

• The purification or isolation process used may have irreversibly affected the behaviour of the protein.

• The structure of the food may cause local differences in composition.

• The exact treatment during processing may be inhomogeneous, for example, the effect of product size on the local temperature during heating.

 

Furthermore, the use of a protein in a product is governed by, on one hand, economic considerations - costs of preparation and handling, availability, and constancy in quality, for example - and on the other hand, by technological considerations. Regarding the latter, the protein should contribute as much as possible to the optimal combination of functional properties required to satisfy the desired product characteristics. For example, egg white, a rather expensive protein preparation, is used in meringues primarily because of its excellent foaming properties. However, its good gelling properties are also of major importance for this application. The combination of functional properties should be optimal and each separate function need not be maximal.

 

In addition to the effects of proteins on the texture and the “mouthfeel” of food products, the complex conformational structure of proteins creates an important source for interactions with flavour compounds influencing the flavour perception of food products. In general, proteins themselves have little flavour of their own. However, the complex conformational structure of proteins creates an important source for interactions with flavour compounds. This ability is exploited in several ways, both with respect to enhancing and masking the flavour of food products. Flavour compounds are often deliberately added to food to enhance its smell and taste. Proteins may then serve to bind these compounds, in other words to act as a reservoir.