Evaluation of Physicochemical, Sensory and Rheological Properties of Stirred Yogurt Fortified with Rice Bran and Lettuce Extract during Shelf-Life

The purpose of this study was to investigate physicochemical, rheological and sensory properties of stirred yoghurt fortified with fermented rice bran and lettuce extract. For lettuce extraction was performed by ultrasound method. Fermented rice bran (2,4,6 and 8%) and lettuce extract (0.5,1,2 and 3%) were added to sterile milk. Starter culture (Lactobacillus bulgaricus and Streptococcus thermophilus) were inoculated at 42 °C. After incubation, sensory evaluation was performed and then physicochemical tests including pH, acidity, synersis, and viscosity were performed on the specimens.The samples were stored (in the refrigerator) for 21 days and they were analyzed every 7 days. The results showed that samples containing fermented rice bran and lettuce extract had a lower pH (4.36 against 4.28) and acidity (92.8 against 96.4) than control samples. Also, by decreasing pH and increasing acidity, which weakened the gel structure of casein micelles, it increased synersis (2.64 against 20.26) and reduced viscosity (5510.52 against 3956.65 mPa.s) in the samples. Also, adding fermentation rice bran and lettuce extract caused changes in the chemical composition of the samples which increased the amount of dry matter and increased the amount of phenolic compounds. The results of sensory evaluation showed that adding lettuce extract to the samples resulted in a significant reduction in sensory evaluation. Yoghurt containing 6% fermented rice bran, and the sample containing 6% fermented rice bran and 2% lettuce extract had the highest sensory rating. The results revealed that yoghurt containing fermented rice bran can be considered as a functional product with good health properties.