• Acidification;
  • aggregation;
  • casein;
  • gelation;
  • microbial transglutaminase;
  • oligomerization;
  • stiffness


The extent of cross-linking by microbial transglutaminase of acid casein in phosphate buffer was varied, and its consequences on the rheology of chemically acidified gels were studied. Gel formation upon acidification was measured by dynamic rheometry and in rotational experiments at a shear rate of 0.002/s. Torque development during gelation under shear, and stiffness and fracture strain of the final gels was significantly affected by the amount of cross-linked caseins. Moderately cross-linked casein exhibited peculiar gelation behavior under shear as monitored with a perspex cylinder device and a video system. Macroscopically visible “threads” with a regular pattern were formed, which appeared to depend on amount and size of cross-linked casein aggregates. From experiments with varying gelation temperature and acidulant concentration, it was observed that larger aggregates result in weaker gels when acidification rate is increased; in native systems, gelation rate did not show any effect.

Practical Applications

Texture and rheology are important quality parameters of acid milk gels that can be modified, among others, by cross-linking milk proteins using microbial transglutaminase. The present results demonstrate that it is crucial to control both the intensity of cross-linking and acidification conditions to obtain products with the desired texture.