Effect of adding soymilk on physicochemical, microbial, and sensory characteristics of probiotic fermented milk containing Lactobacillus acidophilus

Document Type: Full paper (Original article)

Authors

1 Ph.D. Student in Nutrition, Department of Clinical Nutrition, School of Nutritional Sciences and Dietetics, Tehran University of Medical Sciences, Tehran, Iran

2 Department of Food Hygiene and Quality Control, Nutrition and Food Sciences Research Center, School of Nutrition and Food Sciences, Shiraz University of Medical Sciences, Shiraz, Iran

3 Student Research Center, School of Nutrition and Food Sciences, Shiraz University of Medical Sciences, Shiraz, Iran

4 Department of Community Nutrition, School of Nutrition and Food Sciences, Nutrition and Food Sciences Research Center, Shiraz University of Medical Sciences, Shiraz, Iran

Abstract

The aim of the present study was to investigate the effect of addition of soymilk on physicochemical, microbial, and sensory characteristics of milk fermented with Lactobacillus acidophilus. Soybeans were blended 1:5 w/v with distilled water. The prepared soymilk was added to milk in combinations of 20%, 40%, and 60%. Milk was used as the control. All the samples were sterilized and fermented with Lactobacillus acidophilus LA-5 as probiotics. Then, they were kept at 5ºC for 14 days. Microbial count, titratable
acidity, pH, syneresis, color parameters and sensory evaluation were performed during the storage time. Results showed that all the samples possessed minimum effective dose of LA-5 on day 14, although a significant decrease in LA-5 was observed in the sample with 60% soymilk. In each experimental day, there was a noticeable decrease in the pH of the samples. Addition of soymilk to milk also significantly increased syneresis, particularly in samples with 60% soymilk. Sensory evaluations showed that scores of texture,
mouth sense, aroma, and flavor of the samples with 40% and 60% soymilk were significantly lower than other samples. With respect to color, “L” value decreased significantly in the fermented product with 60% soymilk and the decrease was more pronounced with longer storage times. In conclusion, addition of 20% soymilk did not substantially alter physicochemical and sensory characteristics of milk while providing an appropriate growth culture for LA-5. The mixture of milk-20% soymilk can be introduced as a good
probiotic product with lower lactose content and additional nutritional benefits.

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