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

Abstract

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.

Effect of thermal treatment on whey protein polymerization by transglutaminase: Implications for functionality in processed dairy foods

“…The transglutaminase enzymatic activity decreases significantly at pH values higher than 8.0 and lower than 5.0 (Eissa, Bisram, & Khan, 2004). The pH range studied was 6.0-8.0 due to the higher stability of the enzyme under these pH conditions.…”

Small and Large Deformation Rheology of Acid Gels from Transglutaminase Treated Milks

“…2.3.2.13; Ajinomoto Foods Deutschland, Hamburg, Germany) per g milk protein were added to 100 g milk. Actual activity determined via the hydroxamat method, 32 a quasi-standard method used by several researchers (e.g., Eissa et al 24 and Faergemand and Qvist 29 ), was 77.5 U/g. The mixture was incubated in a DC30-K10 water bath [Thermo Electron (Karlsruhe), Karlsruhe, Germany] at 40°C for 1 h. The enzyme was then inactivated by immersing the samples for 10 min in a similar water bath at 85°C, 28 followed by rapid cooling in ice water.…”

“…The work of Imm et al 23 reveals that gels made by acidifying reconstituted mTGase-treated skim milk powder were significantly higher in firmness than gels made by acidifying reconstituted skim milk powder, which was not subjected to enzyme treatment. As regards whey protein systems, Eissa et al 24 obtained firmer gels after incubation with mTGase at alkaline conditions prior to acid-induced gelation than in control samples; after denaturing the whey proteins by heat prior to enzyme treatment at neutral pH, however, subsequent gelation resulted in similar values for the storage modulus. 25 Additionally, similar patterns in the mechanical spectra, but substantial differences in large deformation behavior after cross-linking with mTGase were observed.…”

Nanostructure development during peroxidase catalysed cross-linking of α-lactalbumin

“…For the commercially important whey proteins, functional effects that have been found upon cross-linking include enhanced foaming and foam stability, enhanced emulsion stability, enhanced thermal stability and improvements of gelation properties (Dickinson, Ritzoulis, Yamamoto, & Logan, 1999;Eissa, Bisram, & Khan, 2004;Faergemand, Otte, & Qvist, 1997;Truong, Clare, Catignani, & Swaisgood, 2004). In addition to food applications, various novel non-food applications of enzymatic protein cross-linking are also under investigation, for example in tissue engineering and for wool and leather (Zhu & Tramper, 2008).…”