Enzymatic characterization of transglutaminase from Streptomyces mobaraensis DSM 40587 in high salt and effect of enzymatic cross-linking of yak milk proteins on functional properties of stirred yogurt

Abstract

Streptomyces transglutaminase (TGase) purified from high-salt medium was characterized and applied into yak yogurts. The purified enzyme presented a Michaelis constant of 40.47 mmol and a maximum velocity of 44.44 U/mg of protein for N-carboxybenzoyl-l-glutaminyl-glycine in the hydroxamate procedure. The purified TGase exhibited optimum activity at 55°C and pH 6.0. The enzyme was not stable above 50°C and was stable within a pH range of 5.0 to 10.0 at 4°C for 12h and pH 5.0 to 9.0 at 37°C for 30 min. The TGase activity was not affected by Ca(2+), K(+), Ba(2+), or Na(+), but slightly inhibited by Fe(2+), Mg(2+), and Mn(2+), and strongly by Cu(2+) and Zn(2+). To explore yak milk products, it was used to produce yogurt and TGase was used. It was found that TGase-catalyzed cross-linking was effective in improving functional properties of stirred yak yogurt. Treated yogurt produced a strong acid gel, higher consistency, cohesiveness, index of viscosity, and creamier mouth feel than the untreated product. Furthermore, yak yogurt treated with TGase presented lower wet yak hair or sweat odor, or both. Therefore, TGase can be used to pave the way for exploration of novel yak products to overcome the issues of peculiar wet yak hair or sweat odor, or both.

Technological Characterization of Lactic Acid Bacteria Protease Isolated from Traditional Chinese Fermented Milk

“…As shown in Table 2, yogurts of S. thermophiles showed significantly higher value than that of L. delbrueckii in all level of texture measurements. Firmness, consistency, cohesiveness and index of viscosity of all yogurts in the work were close to that reported by Zhang et al (2012) for Directed Vat Set yogurt. As regards the firmness, the products fermented by L. delbrueckii 3 4.5, SB3 and SB7 were significantly lower than that of others.…”

“…Firmness, consistency, cohesiveness and index of viscosity of all yogurts in the work were close to that reported by Zhang et al . () for Directed Vat Set yogurt. As regards the firmness, the products fermented by L. delbrueckii 3 4.5, SB3 and SB7 were significantly lower than that of others.…”

Influence of milk protein cross‐linking by transglutaminase on the rennet coagulation time and the gel properties

“…Instead, casein polymers were formed, which were too large to enter the gel as indicated by the bands visible at the top of the electrophoretic gel. Zhang et al reported the decrease in κ ‐casein and other protein monomers in cow's and yak's yoghurt milk modified by TGase and the increase in protein aggregates with molecular masses between 66 and 116 kDa compared with samples without TGase treatment. When the addition of TGase was high (2 U g −1 protein) both casein and β ‐lactoglobulin were cross‐linked by TGase creating the polymers with the molecular weight above 200 kDa.…”

Production of a transglutaminase from Zea mays in Escherichia coli and its impact on yoghurt properties

“…MTG derived from S. mobaraensis DSM40587 was extracted by our group and the specific activity reached 2.9 U/mg (Zhang et al . ). Bovine milk was obtained from Mengniu (Harbin, China).…”