Lactobacillus plantarum is a functional probiotic and could be used in yogurt fermentation to improve the function and flavor. However, L. plantarum has relatively poor acid resistance, and cell viability gradually decreases as pH decreases during yogurt fermentation. Therefore, exploring suitable strategies to promote the fermentation of L. plantarum for yogurt processing is important. In the present study, the effects of quinoa protein hydrolysates (QPHs) on the qualities and volatiles of yogurt fermented by L. plantarum were investigated. QPH addition significantly promoted bacterial growth and organic acids production, subsequently improved the water-holding capacity and viscosity of yogurt. QPH addition also increased the overall antioxidant capacity of yogurt, but the DPPH radical-scavenging ability of 1% QPH-supplemented yogurt was significantly greater than that of 2% QPH-supplemented yogurt. Additionally, QPHs promoted the metabolism of L. plantarum and further promoted the production of volatile flavor compounds. Fifty-two volatile compounds (mainly acids, esters, and ketones) were detected in 2% QPH-supplemented yogurt, which was 1.86-fold greater than the number detected in the control samples. Some aroma components, such as nonanoic acid and maltol, were significantly increased, but undesirable volatiles, such as decanal, were decreased. QPH composition analysis indicated that 60.79% of the peptides contained hydrophobic amino acids at the N-terminus or the C-terminus, which may explain QPHs’ strong antioxidant properties.

Objective. This study aimed to delve into the antioxidant potential of small-molecule peptides derived from Lactiplantibacillus plantarum SCS2 (L. plantarum SCS2), targeting hydrogen peroxide- (H₂O₂-) induced rat insulinoma (INS-1) cells. Methods. INS-1cells were pretreated with small-molecule peptides of distinct molecular weights, specifically P1 (1kDa), P2 (15kDa), and P3 (510kDa), which were isolated from L. plantarum SCS2, followed by H₂O₂ to induce oxidative damage in INS-1cells. The oxidative status of the cells was assessed by measuring reactive oxygen species (ROS), malondialdehyde (MDA) concentrations, and antioxidant enzyme activities. In addition, the expression levels of proteins and genes associated with the Kelch-like ECH-associated protein 1 (Keap1)-Nuclear factor erythroid 2-related factor 2 (Nrf2) pathway were examined to elucidate the underlying antioxidative mechanisms of the small-molecule peptides from L. plantarum SCS2. Results. The cellular activity and the activities of antioxidant enzymes, such as superoxide dismutase, catalase, and glutathione peroxidase, were higher after pretreatment with P1 than those after pretreatment with P2 and P3, which led to the suppression of ROS and MDA production. In addition, P1 upregulated mRNA and protein expression of Nrf2 and heme oxygenase-1, significantly decreased mRNA and protein expression of Keap1, and promoted the entry of Nrf2 into the nucleus compared with that in the model group. Conclusion. P1 from L. plantarum SCS2 could activate the Keap1-Nrf2 signaling pathway, thereby ameliorating oxidative damage in INS-1cells.