Characterization of the interaction between Lactobacillus helveticus and Propionibacterium in Swiss cheese

Swiss cheese makers report that some combinations of Lactobacillus helveticus and Propionibacterium freudenreichii cultures result in poor eye and Flavor formation, whereas other combinations perform well. The objectives were to develop a rapid method to predict successful strain pairings and to evaluate peptide metabolism by P. freudenreichii.; A cheese model system was developed to help predict the compatibility of L. helveticus and P. freudenreichii culture pairings. Cheese curds were prepared aseptically from UHT milk using S. thermophilus alone (control) or S. thermophilus plus one of four L. helveticus strains.; Slurry sera produced with different L. helveticus strains differed in their peptide profiles. A total of 126 peptide peaks were identified in all slurry sera. Differences in peptide profiles may contribute to the observed differences in P. freudenreichii growth in the slurry. The slurry serum model has potential for screening P. freudenreichii and L. helveticus pairings for Swiss cheese manufacturing.; Propionibacterium strains have intracellular peptidases to breakdown peptides inside the cell, but little information exists concerning peptide transport in propionibacteria. It is unclear what types) of transporters are used to import the peptides and what their specificities are. The goal of this study is to evaluate specific peptide transport of ten P. freudenreichii strains by using commercially available peptides. The peptide concentration before and after incubation of each peptide with each strain was determined by high performance liquid chromatography to reveal the amount of peptide transported. All ten P. freudenreichii strains were able to transport the Ala-Ala di-peptide 30.89 to 100% peptide transport among the strains.; The intracellular peptidase activities of dairy Propionibacterium strains varied in specificity and activity levels. These differences may contribute to flavor and growth rate variations observed in cheeses manufactured with different Propionibacterium swains. Different peptide transport and peptidase profiles in Propionibacterium will affect their performance with different L. helveticus strains. Peptides produced by L. helveticus and peptide transport and peptidase activity of P. freudenreichii are all swain-specific characteristics. These swain-to-strain differences may contribute to the growth rate and flavor variation of P. freudenreichii swains when paired with particular L. helveticus strains. This study describes several factors that may contribute to interactions between Swiss cheese starter cultures causing some culture combinations to perform better than others. (Abstract shortened by UMI.)...