Influence of transglutaminase on the physical and chemical properties of acid milk gel and cottage type cheese

In the production of a fresh type traditional Lithuanian cottage type cheese acid gelation, induced by lactic acid producing cultures, without rennet addition is used for casein coagulation. The aim of this study was to investigate the possibility to increase the yield of cottage type cheese and to improve the textural properties of cheese using additional cross linking of milk proteins by transglutaminase. The influence of transglutaminase induced cross-linked milk proteins degree on the acid gel formation, rheological properties of acid gel and its impact on the textural properties and yield of cottage type cheese was evaluated. Milk was incubated with 1-4 U g^-1 protein of transglutaminase for 20, 30 and 60 min at 40°C or 50°C temperature. Acid gel was formed by adding lactic acid bacteria after pre-treatment of milk with enzyme or simultaneously with enzyme. Results demonstrated that degree of cross-linked proteins depends on transglutaminase amount, incubation time and temperature. The increase of enzyme amount expanded degree of proteins polymerization from 9.37% at 1 U g^-1 protein of transglutaminase to 19.83% at 4 U g^-1 protein of transglutaminase after 20 min incubation period at 40°C temperature or from 18.51% at 1 U g^-1 protein of transglutaminase to 36.75% at 4 U g^-1 protein of transglutaminase after 60 min incubation time at 50°C temperature. Fermentation process was slowed down by cross-linking of proteins at transglutaminase content (2 and 4 U g^-1 protein) fermentation time increased up to 369 min while the pH at which gel formation started remained at the same level. However, that caused higher gel firmness and incorporation of whey into gel, therefore the increase in cottage cheese yield produced from this gel was observed. The highest cheese yield was obtained in the sample produced from acid gel pre-treated with 3.6 U g^-1 protein transglutaminase at 40°C for 60 min. The excessive protein cross-linking led to the deterioration of textural properties of the cottage type cheese.