Influence of microbial transglutaminase cross-linking on gelation kinetics and texture of acid gels made from whole goats and cows milk

Abstract

The influence of microbial transglutaminase (mTGase) in modifying the functionality of proteins in cows milk has been extensively studied but to a lesser degree for goats milk. On a comparative basis, the effect of cross-linking by mTGase on the physical properties of chemically acidified UHT goats milk and UHT cows milk has been performed. Transglutaminase treatment (3 U mTGase/g protein) of cows and goats milk was conducted at 40 °C for 60 min and terminated by heat treatment (85 °C/10 min) for enzyme inactivation. Gelation was induced by acidification with 40 g.L⁻¹ d-glucono-δ-lactone. Monitoring gel formation by oscillatory rheometry revealed that the incubation of milk with mTGase accelerated gelation, which occurred at a higher pH for cows milk in comparison to goats milk. Electrophoretic analysis revealed that under the same conditions, nearly 31% of the cows milk proteins were cross-linked by the action of mTGase compared to only 9.6% of the goats milk proteins. This resulted in increased gel stiffness and reduced syneresis of the acid gels of both systems, but the extent of the effect depended on the milk source. In general, even with the mTGase treatment, goats milk gels were much weaker than cows milk gels. Despite this fact, the information gained in this study indicates that mTGase might be successfully applied in the production of acidified goat milk products.

摘要

微生物转谷氨酰胺酶(mTGase)在改变牛奶蛋白功能特性方面已有广泛的研究,但是对山羊奶的研究并不多见。实验通过比较分析来研究微生物mTGase交联作用对化学酸化的超高温加热山羊奶和牛奶物理特性的影响。向奶中加入3 U mTGase/g 蛋白的mTGase,在40 °C加热 60 min,然后在85 °C/加热10min目的是灭酶。通过加入40 g∙L^-1 D-葡萄糖酸 -δ-内酯产酸来促进凝胶的形成。凝胶的形成通过振荡流变测定法来进行分析,实验结果表明牛奶在较高的pH比相同pH的羊奶更容易加速凝胶的形成。电泳表明在相同条件下牛奶中31%的蛋白在微生物mTGase的作用下发生了交联作用,而山羊奶只有9.6%的蛋白发生了交联作用。这种结果会导致增加凝胶的硬度和减少酸化凝胶的脱水收缩,但是这种作用程度取决于奶源。总的来说,用mTGase处理奶,山羊奶凝胶比牛奶凝胶质地更软。尽管如此,本研究获得的信息表明微生物mTGase可以成功的应用于酸化山羊乳的加工过程中。