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Polymerization and Gelation of Whey Protein Isolates at Low pH Using Transglutaminase Enzyme

2004; American Chemical Society; Volume: 52; Issue: 14 Linguagem: Inglês

10.1021/jf0355304

1520-5118

Ahmed S. Eissa, Satisha Bisram, Saad A. Khan,

Polysaccharides Composition and Applications

Dynamic and steady shear rheology is used to examine the synthesis of low-pH (∼4) whey protein gels obtained through a two-step process. The first step involves cross-linking of whey proteins at pH 8 and 50 °C using transglutaminase enzyme, while the second step entails cold-set acidification of the resulting solution using glucono-δ-lactone (GDL) acid. During the first step, the sample undergoes enzyme-catalyzed ε-(γ-glutamyl)lysine bond formation with a substantial increase in viscosity. Acidification in the second step using GDL acid leads to a rapid decrease in pH with a concomitant increase in the elastic (G') and viscous (G' ') moduli and formation of a gelled network. We examine the large strain behavior of the gel samples using a relatively new approach that entails plotting the product of elastic modulus and strain (G'γ) as a function of increasing dynamic strain and looking for a maximum, which corresponds to the yield or fracture point. We find the enzyme-catalyzed gels to have significantly higher yield/fracture stress and strain compared to cold-set gels prepared without enzyme or conventional heat-set gels. In addition, the elastic modulus of the enzyme-catalyzed gel is also higher than its non-enzyme-treated counterpart. These results are discussed in terms of the gel microstructure and the role played by the enzyme-induced cross-links. Keywords: Rheology; gel; whey protein; enzyme; transglutaminase; yield stress; cold set