Effects of transglutaminase treatment on functional properties and probiotic culture survivability of goat milk yogurt

The objectives of this study were to investigate the effects of enzymatic cross-linking of milk proteins on the functional properties and probiotic culture survivability of goat milk yogurt. After pre-incubation (50 °C, 1 h) of the milk with microbial transglutaminase [MTGase, 0–4 units (U)/g protein] and subsequent heat inactivation (75 °C, 5 min), yogurt was prepared by inoculating the milk with a commercial probiotic yogurt starter containing probiotic cultures (Lactobacillus acidophilus, Bifidobacteria, and Lactobacillus subsp. casei) and incubating the inoculated milk at 43 °C for 5 h. Compared to the untreated control trial, pretreatment of the milk with MTGase (2 and 4 U/g protein) increased (P < 0.05) the viscosity and decreased the syneresis of yogurt samples. The effect of enzyme treatment was more significant in improving the viscosity of yogurt compared to the method of increasing total solids (TS) in the milk. No significant differences in basic nutrient contents between control and enzyme-treated samples were observed. The probiotic cultures were relatively stable in the goat milk yogurt and their populations remained above 106 CFU/g during the 8-week storage period at 4 °C. No significant differences in rate of change of population of all the three probiotic cultures were observed between the control and the MTGase treated groups. Microbiological analysis shows that the enzymatic cross-linking of proteins seems to have a positive role in the survivability of the probiotic cultures, which requires further investigation. Scanning electron microscopic studies revealed that the microstructure of the enzyme-treated samples appeared denser than the control, suggesting that pretreatment of milk by MTGase could be used to improve the microstructure of the yogurt gel. Results of this study indicate that enzymatic cross-linking of milk proteins by MTGase appears to be an effective means for improving the functional properties of goat milk yogurt. MTGase treatment may be a useful method in the production of probiotic goat milk yogurt products.