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 . An aseptic cheese slurry serum model was developed. Slurry sera were prepared aseptically from UHT milk using S. thermophilus alone (control) or S. thermophilus plus one of four L. helveticus strains. Chemically defined medium lacking peptides or amino acids was supplemented with slurry sera, including the control serum prepared without L. helveticus . These media supported the growth of four of the five P. freudenreichii strains to different extents with some sera prepared with particular L. helveticus strains stimulating the growth of particular P. freudenreichii strains. Slurry sera produced with different L. helveticus strains differed significantly from each other and the control in their peptide profiles. Differences in peptide profiles may contribute to the observed differences in P. freudenreichii growth in the slurry serum medium. The slurry serum model has potential for screening P. freudenreichii and L. helveticus pairings for Swiss cheese manufacturing. Peptide metabolism by P. freudenreichii may affect their growth in cheese. Transport of specific peptides (ala-ala, ala-ala-ala, ala-glu, and glu-glu) in ten P. freudenreichii strains was evaluated. There were significant differences in peptide transport among P. freudenreichii strains. Some peptides are more readily transported by propionibacteria than others. Intracellular peptidase activities (aminopeptidase, PepI and PepX) of 34 different dairy Propionibacterium strains were also evaluated. Significant differences in peptidase activities were observed among the strains. The intracellular peptidase activities of dairy Propionibacterium strains varied in specificity and activity levels. The strain-to-strain differences in peptides produced by L. helveticus , peptide transport and peptidase activity of P. freudenreichii may contribute to the growth rate and flavor variation of P. freudenreichii strains 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.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:swiss cheese lactobacillus propionibacterium peptidase peptide transport
Date of Publication:01/01/2005