The effect of rice flour on survival of Lactobacillus paracasei in fruit yoghurt and its qualitative properties with response surface methodology

In this study, the effect of rice flour on the survival of Lactobacillus paracasei and the qualitative properties of fruit yogurt was investigated during storage, using the response surface method (RSM). For this, rice flour in three ranges of (0, 1.5, and 3%) was added to the milk. Then the milk and was pasteurized at 85ºC for 15 minutes. After cooling, yogurt starter culture and probiotic bacterium were inoculated at 43 ºC and added into sterile containers containing 15% peach puree. The samples were incubated at 42 ºC until reaching pH 4.6 ±0.1. Then the samples were cooled down to 4 ºC and refrigerated at the same temperature until experiment day. Survival of lactobacillus paracasei, pH, amount of moisture, acidity, syneresis, and apparent viscosity and sensory properties were investigated in three periods of (1, 11, and 21 days). The statistical analysis of the results showed that with the increase of rice flour, lactobacillus paracasei count increased and decreased during storage (p<0.05). The addition of rice flour decreased pH, moisture content, syneresis, and increased acidity and apparent viscosity (p<0.05). During storage pH and moisture content decreased and syneresis increased (p<0.05). In the sensorial evaluation of samples, the addition of rice flour increased the consistency score (p<0.05). Flavor score decreased during storage (p<0.05). In conclusion, using 3% of rice flour and a storage period of 7 days was determined as the optimum condition.