Gelling Properties of Tyrosinase-Treated Dairy Proteins

Protein-based viscous gels can augment or replace carbohydrate-based ones for specific nutritional formulations such as in reduced calorie or low-fat food applications. In this study, slurries of whey protein isolates and calcium caseinate mixed with alginic acid (20% T.S.) were subjected to high-shear homogenization (microparticulation) at 27,000 rpm for 2, 3, 4, and 6 min. The resulting slurries were incubated with mushroom tyrosinase (E.C. 1.14.18.1) at levels of 3, 6, and 9 mg/100 g for 15, 30, and 60 min to facilitate gel formation of the alginic acid with the homogenized dairy proteins. The results indicate that the time of high-shear homogenization had significant (P < 0.05) effect on the viscosities of the gels. Highest gel viscosity was obtained with 6 mg tyrosinase at 60 min, but increases in gel viscosity depended on time of shear, with 2 and 4 min shear resulting in higher viscosity (484 and 6,143 cP) and stronger complex viscosity (49 and 38 Pa.s at 1 rad/s), respectively, compared to the control (69 cP) and (12 Pa.s at 1 rad/s). Gels were stable in refrigerated storage up to 240 h, strengthened with time of refrigeration storage, and became significantly more viscoelastic. Optimal viscous properties were obtained at 4 min microparticulation, 60 min incubation, and 6 mg tyrosinase treatment.