Viscosity changes of probiotic yoghurt with transglutaminase during storage

The aim of this study was to determine the effect of the quantity of transglutaminase as well as conditions of its application (direct, or after activation by milk heating for 2 h at 40°C and for 1 min at 80°C), on yoghurt viscosity manufactured from two kinds of low fat milk (0.1 % w/w fat and 0.5% w/w fat) during 10 days of storage. The fermentation in both series started after the adequate amounts of probiotic starter culture ABT-4 (Chr. Hansen A/S Denmark) were added to the milk at 43°C. After milk fermentation at pH 4.5, probiotic yoghurt samples were cooled to 8°C, gently homogenized and packed in plastic containers and stored for 10 days, at +4oC. Viscosity of all samples was measured at 5°C on a Haake Rheostress 600 viscosimeter. On the basis of the obtained results it can be concluded that yoghurt samples produced with low level of transglutaminase activated prior to fermentation have significantly better rheological properties than the samples produced without activation and yoghurt control. Generally, the application of low level transglutaminase in low - fat yoghurt production improves overall rheological properties of the final product