The role of lactic acid bacteria in production of bioactive peptides in fermented milk with antioxidant and antidiabetic properties

Type II diabetes is one of the metabolic diseases that leads to the main complications for human health. Food-derived bioactive peptides were shown to have substantial potential for use in diabetes management. This study assessed how the activity of lactic acid bacteria (LAB) isolated from Iranian dairy products improved milk's antioxidant and antidiabetic properties with an insight into the activity of produced peptides. The inhibition of 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) was used to measure the antioxidant activity, and the inhibition of α-amylase and α-glucosidase enzymes was used to investigate the antidiabetic properties. The results of antioxidant activity showed that the milk fermented by L. delbrueckii PTCC 1900 (59.43%, IC₅₀ = 0.2 mg protein) and L. paracasei ssp. paracasei PTCC 1945 (85.93%, IC₅₀ = 0.01 mg protein) had the highest DPPH and ABTS free radical scavenging at 48 h, respectively. The highest α-amylase and α-glucosidase inhibitory activities were observed, respectively, in milk fermented by L. helveticus PTCC 1930 (35%, IC₅₀ = 0.28 mg protein) and L. paracasei ssp. paracasei PTCC 1945 (50%, IC₅₀ = 0.03 mg protein) strains after 48 h. In addition, peptide fractions with a lower molecular weight demonstrated the highest proteolysis, antidiabetic, and antioxidant properties (p < 0.05). These results showed bioactive peptides derived from microbial fermentation can play an important role in creating the appropriate antidiabetic and antioxidant properties. Additionally, the results showed that the antidiabetic and antioxidant properties depended on the type of strain. Besides, the findings revealed a significant possibility for selected LAB strains to produce fermented milk as a nutraceutical or functional food.