Proteolytic activity of Lactobacillus rhamnosus GG and Lactobacillus paracasei in a dairy drinking dessert and its effect on antioxidant activity of product: Comparing the fermented and non-fermented type

Bioactive peptides are released by proteolytic enzymes of lactic acid bacteria (LAB) during fermentation process which some have antioxidant activity according to their amino acids sequences. The aim of this study was to investigate the proteolytic activity of Lactobacillus rhamnosus GG and Lactobacillus paracasei in drinking dessert mix and to evaluate the antioxidant capacity of this synbiotic drinking dessert in two types of fermented and low-lactose non-fermented. Proteolytic activity of probiotic bacteria was evaluated using the OPA indicator for amino acid residues by optical absorbance. The antioxidant activity also evaluated by optical absorbance method according to DPPH radical scavenging activity. In fermented sample, proteolytic activity of L. paracasei during fermentation time was not significant (P < 0.05), but L. rhamnosus GG had the highest proteolytic activity after 17 h of incubation. During storage time, the highest proteolytic activity for L. paracasei was in 7 and 4 days after storage (P < 0.05) and for L. rhamnosus GG was in the first day of storage. In non-fermented sample the most activity of L. paracasei was related to the first day of storage (0.5). But L. rhamnosus GG proteolytic activity was much less (0.12) and was related to the second day. Antioxidant activity of fermented dessert was not significant which shows that these two probiotic bacteria has no significant antioxidant activity. Comparing the fermented sample and non-fermented drinking dessert, the non-fermented one exhibited higher antioxidant activity due to containing cocoa powder which has antioxidant component.