Mandana Mahmoudi

In this study, single and co-cultures of proteolytic Lactobacillus delberueckii subsp. bulgaricus ORT2, Limosilactobacillus reuteri SRM2 and Lactococcus lactis subsp. lactis BRM3 isolated from different raw milk samples were applied as starter cultures to manufacture functional fermented milks. Peptide extracts from fermented milk samples were evaluated after fermentation and 7 days of cold storage for proteolytic, angiotensin-converting enzyme (ACE) inhibitory and antioxidant activity by different methods including 2, 2′-diphenyl-1-picrylhydrazyl (DPPH), ferric-reducing antioxidant power (FRAP), OH-radical scavenging, and total antioxidant (molybdate-reducing activity). The highest proteolysis was found in milk fermented by co-cultures of three strains. Fermentation with the mentioned bacteria increased ACE inhibitory and antioxidant activity of the final products which were dependent on peptide concentration. The crude peptide extract obtained from fermented milk with triple co-culture showed the highest ACE inhibitory activity (IC₅₀ = 0.61 mg/mL) which was reduced after 7 days of cold storage (IC₅₀ = 0.78 mg/mL). Similar concentration-dependent activities were found in antioxidant activity at different antioxidant assays. Overall, high proteolytic activity resulted in increased ACE inhibitory and antioxidant activities, but the highest activity was not necessarily found for the samples with the highest proteolytic activity. The results of this study suggest the potential of using co-cultures of L. delberueckii subsp. bulgaricus, L. reuteri and L. lactis subsp. Lactis to manufacture antihypertensive fermented milk.

The viability of Bifidobacterium animalis (ATCC 25527) and Lactobacillus rhamnosus (ATCC 7469), study of interaction between probiotic and starter and their effect on the properties of Iranian white cheese were investigated during 60 days of ripening. The results indicated that probiotics did not exert any effect on the growth of commercial starters, but starters showed a synergistic effect on the growth of probiotics, and probiotics survived above the recommended level for the therapeutic minimum (10⁶–10⁷ cfu/g) after 60 days. Addition of probiotic adjunct did not alter the chemical composition except for moisture and protein. Also, the highest pH value was in probiotic cheeses without starter.