Polymerization and gelation of whey protein isolates at low pH using transglutaminase enzyme.
Dynamic and steady shear rheology is used to examine the synthesis of low-pH (approximately 4) whey protein gels obtained through a two-step process. The first step involves cross-linking of whey proteins at pH 8 and 50 degrees C using transglutaminase enzyme, while the second step entails cold-set acidification of the resulting solution using glucono-delta-lactone (GDL) acid. During the first step, the sample undergoes enzyme-catalyzed epsilon-(gamma-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'gamma) 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.
Eissa
Ahmed S
AS
Department of Chemical Engineering, North Carolina State University, Raleigh, NC 27695-7905, USA.
Bisram
Satisha
S
Khan
Saad A
SA
D003080:Cold Temperature; D004591:Electrophoresis, Polyacrylamide Gel; D005782:Gels / Q000737:chemistry*; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D008855:Microscopy, Electron, Scanning; D008894:Milk Proteins / Q000737:chemistry* / Q000378:metabolism*; D011108:Polymers / Q000737:chemistry*; D011503:Transglutaminases / Q000378:metabolism*; D014783:Viscosity; D000067816:Whey Proteins
D005782:Gels; D008894:Milk Proteins; D011108:Polymers; D000067816:Whey Proteins; D011503:Transglutaminases