Effects of fat on relationship between particle size and physical properties of cross-linking yogurt by purified Transglutaminase from Streptomyces mobaraensis DSM 40587

The purified TGase produced by Streptomyces mobaraensis DSM 40587 from high salt medium was applied to whole and skim milk yogurt. During yogurt fermentation, no negative effect of TGase on fermentation time was found. Protein cross-linking by TGase was enhanced at varying concentrations from 0 to 5 U/g protein, resulting in a increase of apparent viscosity and decrease of syneresis. Furthermore, texture parameters were improved. However, extensive cross-linking resulted in too big size of the aggregates. The formation of these polymers resulted in a coarse texture of yogurt. Fat had no impact on the apparent viscosity and texture parameters, but significant changes in cross-linking of protein, syneresis and the sizes of the aggregates. From the range of TGase concentrations examined for properties of yogurt, the optimal level of TGase for skim milk yogurt was 1 U/g protein; however, for whole milk yogurt was 3 U/g protein.