Propionibacteria and facultatively heterofermentative lactobacilli weakly contribute to secondary proteolysis of Emmental cheese

Proteolysis is a major event during cheese ripening.In Emmental cheese, the contribution of plasmin and thermophilic lactic starters to proteolysis has been well established.Our aim was to assess the contribution of each ripening flora to secondary proteolysis.With this aim, we used the aqueous phase (or juice) of Emmental cheese as a culture medium, which contains the enzymes released by thermophilic starters.Crude juice (containing all cheese flora) and cell-free juice either inoculated with two propionibacteria (PAB) strains or uninoculated (control), were incubated under anaerobiosis at 24 o C for 20 d.Free amino groups and free amino acids, bacterial growth and organic acids were followed throughout the incubation time.Facultatively heterofermentative lactobacilli (FHL) represented the main flora growing in crude juice up to 10 d incubation.FHL and PAB respectively reached 4.0 × 10 8 and 1.0 × 10 10 cfu .mL -1 of juice and consumed citrate and lactate, in accordance with that already observed in cheese.The level of amino groups increased linearly during incubation time by a factor of 1.9 in crude juice, 1.7 in cell-free juice and only 1.5 in juice inoculated with PAB strains, showing that the enzymes of thermophilic starters are the main contributors to secondary proteolysis.FHL growth resulted in a 16% increase in free amino acids compared to cell-free juice and in exhaustion of Arg and His.Both PAB strains caused a 18-27% decrease in free amino acids and also modified the amino acid distribution, with consumption of Asp, Gly, Glu, Ser and Ile.secondary proteolysis / Propionibacterium / facultative heterofermentative lactobacilli / Emmental cheese / free amino acid Résumé -Les lactobacilles hétérofermentaires facultatifs et les bactéries propioniques ont une faible contribution à la protéolyse secondaire de l'Emmental.La protéolyse est un phénomène majeur dans l'affinage du fromage.Dans l'Emmental, la contribution de la plasmine et des levains thermophiles à la protéolyse secondaire a été bien établie.