Properties of Non-Fat Yoghurt as Influenced by The Incubation Temperature of Exopolysaccharide Producing Culture

Different incubation temperatures (40°C, 42°C and 45°C) were used in making non-fat yoghurt. Exopolysaccharides producing culture consists of Streptococcus thermophilus, Lactobacillus delbrueckii ssp. bulgaricus and Lactobacillus fermentum with (1:1) or without commercial yoghurt starter culture (YC-x11) were used. Treatments were examined during the storage. Results showed that, the fermentation time decreased significantly by increasing the incubation temperature, further decrease of the incubation period was observed by using a combination of YC and EPS cultures. The higher pH value and lower acidity were observed by using EPS instead of YC cultures, while using higher incubation temperature improved development of the acidity. The highest acetaldehyde content and water holding capacity were achieved by using a mixture of the tested cultures at 42°C., followed by 45°C. The same trend was noticed for the viscosity parameter; as compared with the control (YC culture at 42°C), which had lowest value. Yoghurt made using EPS culture at 40°C resulted in a very high wheying-off, but it could be treated by the combination of EPS and YC cultures at the same temperature. More improvement, however, could be achieved by increasing the incubation temperature to 42°C. Panelists gave the highest sensory scores  to the yoghurt made by a mixture of EPS and YC cultures at 42 and 45°C. The results revealed that the yoghurt made with EPS and YC starter cultures (1:1) at 42°C was the most accepted and were of the best rheological properties, compared with the other treated samples.