The effect of microbial transglutaminase on microbiological, chemical, textural and sensory properties of yogurt.

This study was performed to investigate the effects of microbial transglutaminase treatment on yogurt quality during storage. Three yogurt samples were produced. The first was a control, the second was produced using milk treated with 0.2% transglutaminase inactivated for 1 minute at 80°C after incubation for 2 hours at 40°C, and the third was produced using milk treated by 0.2% transglutaminase but without incubation of the enzyme. All yogurt samples were stored at 4±1°C and analysed for dry matter, fat, protein, acetaldehyde, titratable acidity, syneresis, viscosity, gel strength, pH, yogurt bacteria, total psychrotrophic aerobic micro-organisms, moulds and yeasts, and sensory properties on days 1, 3, 7, 10, 14 and 21 of storage. Treatment with 0.2% transglutaminase had a very significant effect on titratable acidity, gel strength, syneresis, counts of yeasts and moulds, and consistency-in-spoon (p<0.01). Significant effects on pH, appearance, mouthfeel and overall acceptability (p<0.05) were also demonstrated. Enzymatic inactivation affected the counts of yeasts and moulds, pH, syneresis, mouthfeel and overall acceptability in the MTGase-treated samples. In addition, storage time had a very significant effect on pH, titration acidity, syneresis, counts of Lactobacillus delbrueckeii subsp. bulgaricus, total psychrotrophic bacteria, yeasts and moulds (p<0.01), as well as significant effects on gel strength, counts of Streptococcus thermophilus and consistency-in-spoon (p<0.05).