Peptidase activity of four yeast species frequently encountered in dairy products - comparison with several dairy bacteria

In this work, peptidases of four yeast species frequently encountered in dairy products, i.e. Kluyveromyces lactis, Saccharomyces cerevisiae, Debaryomyces hansenii and Pichia anomala, were investigated with respect to activity towards beta-casein-derived peptides and compared with the activity of six bacterial species, i.e. Lactobacillus helveticus, Lactobacillus plantarum, Leuconostoc lactis, Pediococcus pentosaceus, Bifidobacterium bifidum and Brevibacterium linens. Cell-free extracts (CFE) obtained by mechanical disruption were standardised in terms of protein content, then added to a beta\-casein hydrolysate. The free amino acid release at 24degreesC and pH 5.7 was monitored over a period of 168 h. Free amino acid and peptide profiles were determined by chromatography. The yeasts tested exhibited a higher peptidase activity than all bacterial species except Lb. helveticus, which had comparable activity. Yeast CFE were less efficient in proline release compared with Lb. helveticus, but more efficient at degrading beta-casein putative phosphorylated peptides. These results support the proposition that yeasts can significantly influence proteolysis in cheese. (C) 2002 Elsevier Science Ltd. All rights reserved.