The effect of probiotic strains on the proteolytic activity and peptide profiles of lupin oat-based yoghurt

Abstract

Plant-based yoghurt is on the rise, addressing both sustainability and innovation in food production. The macro-molecular changes driven by bacterial strains during fermentation of plant-based yoghurt leading to diverse nutritional functionality, however, is overlooked. Here, the lupin-oat milk yoghurt was developed using three distinctive commercial starter cultures composed of Lactobacillus delbrueckii sub bulgaricus, Streptococcus thermophilus and Lactobacillus rhamnosus for yoghurt 1 (Y1), Lactobacillus delbrueckii sub bulgaricus, Streptococcus thermophilus and Lactobacillus paracasei for yoghurt 2 (Y2), Lactobacillus plantarum and Bifidobacterium sps for yoghurt 3 (Y3). The post-acidification, proteolytic activity, amino acid composition, cell viability, peptide profile and angiotensin-converting enzyme (ACE) inhibitory activity were investigated during seven days of refrigeration at 4 °C. Gel electrophoresis and size exclusion chromatography (SEC) of yoghurts, showed substantial degradation of proteins into low molecular weight protein fractions (45, 55 and 75 kDa) which are complemented by an increase in small polypeptides with a molecular weight of <20 kDa. The bacteria did not fully utilize the released peptides, leading to significant accumulations in the medium. This observation indicates the potential presence of bioactive compounds with beneficial effects. The SEC peak fraction containing a smaller peptide size ranging from 0.059 to 0.87 kDa showed better ACE inhibitory activity. A comprehensive analysis of peptide profiling of the yoghurts was done using Nano UPLC-MS/MS which showed co-cultures promoted the formation of peptides. After undergoing bacterial fermentation, the number and types of peptides followed the Y3>Y1>Y2 sequence. This study emphasizes the potential of lupin-oat yoghurts peptides as a functional component.