Influence of raw milk microflora and starter cultures in cheese on protein hydrolysis and peptide generation during digestion

Do bacterial strains in cheese have an impact on the protein hydrolysis during human digestion, and if so, does a higher microbial diversity lead to the generation of a higher number of different peptides after digestion? Cheese bacteria are responsible for the hydrolysis of proteins already during cheese ripening. These bacterial cultures are introduced at different steps of the cheese manufacturing process. First, the raw milk flora that is dependent on the milk heat treatment before the cheese manufacturing process, is a major source of a variety of bacteria. Second, starter cultures, needed for a successful acidification of the cheese curd are added to prevent side fermentations. Third, addition of cultures is made for improving flavor or accelerating the ripening process, depending on the type of cheese. Because of bacterial proteolytic activity, proteins in cheese are partially hydrolyzed, depending on the ripening time and are further digested by gastric and pancreatic proteases, after consumption, to the level of small peptides and free amino acids. In order to elucidate possible differences in proteolysis depending on the presence of different bacteria, Swiss Raclette cheeses were produced either from raw or pasteurized milk with or without addition of a proteolytic bacterial strains (Lactobacillus helveticus) and ripened during 120 days. The microbial diversity and the relative abundance of specific strains in the different cheeses was assessed after 24 hours, 80 and 120 days of cheese ripening by sequencing the hypervariable regions V1-V2 of the 16S rRNA genes. Moreover, protein hydrolysis in the different cheeses was analyzed with gel electrophoresis, mass spectrometry, and HPLC after in vitro digestion, applying a static (Infogest) and a dynamic (DIDGI®) oro-gastrointestinal in vitro digestion protocol. In order to gain information on the influence of bacterial strains on protein hydrolysis, the 16s meta-genomic and 16s meta-transcriptomic results were correlated with protein and peptide patterns