Evaluation of Microbial, Antioxidant, Proteolytic Degree and ACE Inhibitory Properties of Yogurt Produced By Adjunct Cultures Isolated From Traditional Iranian Yogurts

Several factors are considered during production of yogurt, among which selecting the accurate starter and or adjunct culture is one of the most important factors. This study was aimed to measure the degree of proteolysis, ACE-inhibitory, microbial and antioxidant activity of yogurt produced by a commercial starter supplemented with native co-cultures isolated from traditional yogurts during a 20-days of storage. All treatments were also compared with the commercial culture as control. Initially, five strains of Lactobacillus lactis, two strains of Lactobacillus helveticus, one strain of Lactobacillus delbrueckii, one strain of Pedicucus pentosaseus and one strain of Vissella sibaria used to inoculate into 40 yogurt samples in a completely randomized factorial design with two replications. The samples were kept at 5 ˚C for 20 days and investigated for their physicochemical properties (pH and acidity), degree of proteolysis, ACE-inhibitory, microbial antioxidant activity. The results of statistical analyses showed that application of native co-cultures was significantly increased the degree of proteolysis, ACE-inhibitory, and antioxidant activity of the samples. Our findings showed that, yogurt inoculated with the native strains of Lactobacillus lactis had the highest scores for ACE-inhibitory and antioxidant activity. In all co-cultures, ACE-inhibitory (47%) and antioxidant activity (58%) exhibited a positive correlation with proteolysis. Our results show that co-cultures greatly affect the ACE-inhibitory and antioxidant activity, which can be used in the production of functional food stuffs.