Whey Proteins and their Thermal Denaturation - A Review

1. Whey and Whey Products Whey can be defined in a very general sense as liquid remaining after removal of casein from milk. Casein can be separated from milk in a variety of ways resulting in the production of a number of different types of whey, each of which can be identified on the basis of the method of casein removal. From an industrial viewpoint there are two principal types of whey (IDF, 1978; Nielsen, 1974); sweet and acid wheys. These are by-products of cheese or rennet casein and acid casein manufacture, respectively. Acidification may be by direct addition of mineral acid or by in situ production of acid by added starter bacteria Sweet whey has a minimum pH of 5.6 and acid whey a maximum pH of 5.1 (IDF, 1978). Whey composition varies depending on milk source, processing methods used and the cheese or casein type but typically it contains ~ 50% of the total solids of the original milk and includes lactose, proteins, minerals and vitamins. Data on whey composition include those by Roeper (1971), Cerbulis, Woychik and Wondolowski (1972), Josephson, Rizvi and Harper (1975), Glass and Hedrick (1976a, b) and Marshall (1982). Table 1 lists the average composition of some types of whey. Whey was traditionally regarded as a waste product and was generally disposed of as effluent or as an animal feed. However, it has now come to be regarded as a product whose valuable constituents can be constructively utilized by the food industry, where there has been increased recognition that the proteins, lactose and possibly even the salts in whey are valuable nutrients. Impetus for whey utilization is due to the increased use of functional proteins in processed foods and to the development of new technologies for the economic recovery of such protein from whey. Heating has direct relevance in the development of whey processing techniques and influences the functionality of whey protein products; it is a major technological treatment, either as a process per se or as part of a process. Heating induces changes in whey constituents, especially the proteins, which have a major influence on the efficiency of the process and on the quality of the product. Thus, heating has direct effects on both the structure and functionality of these proteins in food systems. An understanding of the effects of heat on proteins, i.e. denaturation and aggergation, might permit manipulation and control of these phenomena in order to permit greater product and process control and/or to develop new processes or products with predictable or tailor-made functional properties. For example, Richert, Morr and Cooney (1974) and Richert (1979) showed that controlled heating, to induce limited 43