Effect of asparagus extract and green tea extract on viability of probiotic bacteria, antioxidant activity and sensory properties of kefir

Kefir is one of the fermented milk products that plays a major role in nutrition and human health. The aim of this study was to investigate the effect of adding asparagus extract and green tea extract on survival of probiotic bacteria, antioxidant activity and sensory properties of kefir. Different concentrations (0.5, 1 and 1.5%) of asparagus extract and green tea extract were used in kefir and the samples were stored at 4˚C for two weeks.The results showed that addition of herbal extracts decreased pH and increased acidity and antioxidant activity of the samples (p≤0.05). The highest antioxidant activity was related to the sample containing 1.5% green tea extract. During storage time, pH of the samples decreased, but acidity increased significantly (p≤0.05). There was no significant difference between samples in terms of viability of Bifidobacterium lactis and Lactobacillus acidophilus (p>0.05). The viability of probiotic bacteria decreased significantly (p≤0.05) during storage but in all samples, the number of bacteria was more than 108 CFU/ml until the end of the storage period. The sample containing 1.5% asparagus extract had the highest score of overall acceptance. Therefore, this sample was selected as the best treatment.