Assessing the proteolytic and cheese ripening properties of single strains of Lactococcus in miniature cheeses

The performance of Il single strains of Laetoeoeeus (Le.laetis ssp.eremoris 223, 227, 250, 255, 267, 303, AM 1 and SK Il and Le.laetis ssp.laetis UC317 [non-bitter strains], and Le.laetis ssp.cremoris Wg2 and HP [bitter strains]) was studied in miniature Cheddar-type model cheeses.Different inocula were used to give equivalent rates of acidification during manufacture and the cheeses made differed in flavour development and proteolysis during ripening.Urea-polyacrylamide gel electrophoretograms (PAGE) of the water-insoluble fraction (WISF) of ail cheeses were similar after 2 and 4 months of ripening, while the level of water-soluble nitrogen (WSN; as % of total N) showed only small differences between cheeses made with different starter strains.The cheese made with Le. laetis ssp.eremoris Wg2 differed considerably from the other cheeses as indicated by urea-PAGE of the water-soluble fraction (WSF), reverse-phase high performance Iiquid chromatography (RP-HPLC) of the 70 % ethanol-soluble and -insoluble fractions of the WSF, concentration of amino acids and flavour characteristics; it had the highest pH (5.7) and the highest concentration of most of amino acids except Asp, Ile and Arg after 4 months of ripening.The cheese made with Le. laetis ssp.cremoris SKII received the highest score for flavour and that made with Wg2 received the lowest score.The results ofthis study indicate that the strain(s) of Laetocoeeus used as starter plays an important role in the biochemistry of cheese ripening and produces a characteristic profile of peptides and amino acids.© InralElsevier, Paris.single strain starters / miniature cheese / proteolysis Résumé -Évaluation des propriétés protéolytiques de souches pures de Lactococcus pendant l'affinage de fromages miniatures.La performance de Il souches pures de Laetoeoeeus [Le.laetis ssp.eremoris 223,227,250,255,267,303, AMI et SKII et Le.laetis ssp.laetisUC317 (souche