R. J. MCCARTHY and P. Courtney. Ohio State University, Columbus, OH 43210
Swiss cheese manufacture is dependent on the growth and enzymatic activities of Streptococcus thermophilus, Lactobacillus helveticus or L. delbrueckii, and Propionibacterium freudenreichii. Propionibacterium growth may be dependent on free amino acids and peptides in the cheese derived from casein degradation by Lactobacillus proteolytic enzymes. The availability of particular amino acids in the cheese is influenced by the Lactobacillus strain and ripening conditions. The amino acid requirements of a particular Propionibacteirum strain may affect its performance in combination with a particular Lactobacillus strain.
The objective was to determine the amino acid requirements of Propionibacterium strains isolated from starter cultures and Swiss cheeses.
Ten P. freudenreichii strains were grown in chemically defined medium. Growth was monitored spectrophotometrically. Complete medium containing all 20 amino acids and a medium lacking amino acids were used as controls. Twenty media, each lacking one amino acid, but containing the other 19, were used to assess the requirement for each amino acid.
All ten strains were able to grow in the absence of amino acids, but at a markedly reduced rate compared to the complete medium, suggesting partial auxotrophy for at least one amino acid in all strains. Strains ranged from 1-20 partial amino acid auxotrophies with most requiring 2-4 amino acids for maximum growth. Partial methionine auxotrophy was encountered in all but one strain. Other partial auxotrophies included those for alanine, glutamine, glycine, histidine, lysine, tryptophan, and tyrosine. For two strains, the absence of most amino acids, individually, stimulated growth compared to the complete medium. The absence of glutamine, lysine or tyrosine promoted lysis in some strains upon reaching stationary phase.
Dairy Propionibacteirum strains differ in the number and nature of their partial amino acid auxotrophies. These differences may contribute to the strain-to-strain variation in growth and gas production during Swiss cheese ripening.
Session 17A, Dairy Foods: Cheese and microbiology