Comparative evaluation of selected strains of lactobacilli for the development of antioxidant activity in milk

Species of Lactobacillus are widely used as starter cultures in the dairy industry and have been reported to play a significant role in the production of bioactive peptides in fermented dairy products. The aim of the present study was to screen selected strains of Lactobacillus for their ability to generate antioxidant activity during the fermentation of milk and to correlate their proteolytic activity with antioxidative peptide production. Skim milk fermented with 19 strains of Lactobacillus from ten species was evaluated for antioxidant activity by 2, 2′-azinobis (3-ethylbenzothiazoline-6-sulphonic acid) decolourization assay. The whey fraction of fermented skim milk showed radical scavenging activity ranging from 0.12 to 0.49 mmol·L−1 Trolox equivalent antioxidant capacity. The proteolytic activity of the different strains ranged from 0.40 to 2.25 mmol·Leu·L−1. Seven strains including Lactobacillus delbrueckii subsp. bulgaricus NCDC08, Lactobacillus plantarum NCDC25, Lactobacillus casei subsp. casei NCDC17, Lactobacillus rhamnosus NCDC24, Lactobacillus paracasei subsp. paracasei NCDC63, Lactobacillus fermentum NCDC141 and Lactobacillus helveticus NCDC288 exhibited a positive correlation between antioxidant and proteolytic activity. On hydrolysis of casein with cell-free extract from these seven strains, L. rhamnosus NCDC24, L. casei subsp. casei NCDC17 and L. paracasei subsp. paracasei NCDC63 showed a significant (P < 0.05) increase in radical scavenging activity. The low molecular weight peptides (<3 kg·mol−1) represented 60–70% of the total radical scavenging activity for these three strains. The development of antioxidant activity was found to be strain specific and that these strains of Lactobacillus may be useful in developing functional foods to combat oxidative stress.