Effect of a low temperature step during fermentation on the physico-chemical properties of fat-free yogurt

The effect of a cold step during the fermentation of fat-free yogurt was studied. Fermentation of skim milk was stopped at approximately pH 5.2 by reducing the temperature to 4°C for 30-120min. After each cold step, fermentation continued at 40°C to approximately pH 4.6. Yogurts from milk subjected to a cold step exhibited a protein matrix with a strong solid-like behavior and improved whey holding capacity when compared with control yogurts (uninterrupted fermentation). TEM showed a strong micellar aggregation in the case of control yogurts but a thin casein protein matrix for yogurt stored at 4°C for 60min before the fermentation was complete. These findings indicate that introducing a cold step during the fermentation process is a potential method to improve the resistance to syneresis of fat-free yogurt without the need to add stabilizers or gums that may be considered undesirable by consumers.