Whey proteins have increasingly made their way into human foods. For many years, whey was considered a by-product of cheese manufacture and was seen as an environmental pollutant (1). The main food usage was as animal feed, although dried whey was sometimes used as a filler in human foods (1, 2). In the 1970s, ultrafiltration processes brought whey protein concentrates with better properties than whey powders. From a nutritional perspective whey proteins are important because they are highly digestible, provide all essential amino acids, and are relatively cystine-rich (1). In fact, the major bovine whey proteins, β-lactoglobulin, α-lac-talbumin, immunoglobulins, and bovine serum albumin contain two, four, four and 17 cystine per molecule, respectively (3). Cystine is the disul-fide form of cysteine and can be reduced to two moles of cysteine by cells for use in various processes including synthesis of the antioxidant glutathione (GSH) (4).
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