ENZYMATIC MODIFICATION THROUGH MICROBIAL TRANSGLUTAMINASE ENHANCES THE VISCOSITY OF STIRRED YOGURT

Among others, dairy proteins and, especially, the caseins are well-suited substrates for enzymatic modification by microbial transglutaminase. Apart from studies on chemically acidified dairy gels, some research has been performed on the impact of cross-linking on rheology and texture of set yogurt. In this study, stirred yogurt was produced from skim milk that was incubated with transglutaminase. Dry matter of the base milk and starter cultures were varied at two levels, and the products were analyzed after 2 and 9 d of storage. The rheological measurements revealed a significant but shear rate-dependent impact of enzymatic cross-linking on the properties of stirred yogurt. Under steady-shear conditions, the viscosity-enhancing effect was more pronounced at low shear rates or shear stresses, pointing on enhanced interactions among the aggregated proteins in the products made from cross-linked milk. The cross-link-induced viscosity-enhancing effect diminished with increasing shear rates. Microbial transglutaminase represents an interesting tool for texture modification of protein-containing foods. The formation of new covalent cross-links among and within protein molecules generates considerable changes in the technofunctional properties of the final products. Acid gels, such as yogurt, made from enzyme-treated milk are characterized by reduced syneresis and improved viscosity. A better understanding of the enzyme-catalyzed impact on the rheological behavior of stirred yogurt may help create new products with interesting properties.