Lait 73 (1993) 265-279
DOI: 10.1051/lait:1993325

Activité protéolytique de souches de lactobacilles thermophiles isolées de levains et de Comté. I. Validation sur minifromages des techniques de laboratoire

Y. Bouton^{a, b}, P. Guyot^{a, b}, A. Dasen^a and R. Grappin<sup>a

a</sup>  Station de recherches en technologie et analyses laitières, INRA, BP 89, 39801 Poligny Cedex, France
^b  Comité interprofessionnel du gruyère de Comté, avenue de la Résistance, 39800 Poligny

(Reçu le 16 novembre 1992; accepté le 3 février 1993)

Abstract - Proteolytic activity of Lactobacilli strains isolated from starters and Comté. I. Validation of laboratory tests on mini-cheeses
Fifty Lactobacillus (helveticus and delbrueckii subsp lactis) strains, isolated from starters and cheeses (Comté), were purified, identified, and classified, according to their acid production level and especially to their proteolytic activity evaluated by two different tests: free amino acids by 2,4,6 trinitrobenzenesulfonic acid (TNBS) and leucine-aminopeptidase activity (Lap). Principal component analysis was used for strain grouping. Four Lactobacillus and 2 Streptococcus salivarius subsp thermophilus strains were chosen to study the relationship between the proteolytic activity of lactic bacteria strains assessed with laboratory tests and the nature and extent of proteolysis measured on cheeses. Experimental mini-cheeses were made with single strain and strains associations. Cheeses were made from raw microfiltrated milk to eliminate the influence of original microflora. Sixteen mini-cheeses were made using the conventional Gruyère cheese process. Classification of strains, according to laboratory test results, did not show any significant correlation when the tests were carried out on single or mixed cultures. More data are necessary to obtain a better understanding of the interaction between Streptococci and Lactobacilli. Different classifications of the proteolytic activity of Lactobacilli strains were also obtained when the characterization fie TNBS and Lap methods) was made on mini-cheeses rather than with laboratory tests. Because the origin of the milk, as well as the ripening conditions, may influence the overall cheese proteolysis, model cheeses will have to be developed to study the behaviour of starters.

Résumé - Afin d'étudier les relations existant entre les mesures de l'activité protéolytique de souches de bactéries lactiques effectuées en laboratoire et celles observées sur fromages, 6 souches de bactéries lactiques thermophiles isolées de levains et de fromages (Comté) ont été caractérisées selon leur potentiel protéolytique évalué par 2 méthodes : mesure des groupements aminés libres par l'acide 2,4,6 trinitrobenzène sulfonique (TNBS) et détermination de l'activité leucine-aminopeptidase (Lap). Des essais en minifabrications de fromages, effectués soit en monosouche soit en associations de souches, ne montrent aucune corrélation significative entre les tests de laboratoire et les mesures de protéolyse réalisées sur fromages avec les méthodes TNBS et Lap.

Key words: 2,4,6 trinitrobenzenesulfonic acid / leucine-aminopeptidase / mlni-cheese / Lactobacillus / proteolysis

Mots clés : acide 2,4,6 trinitrobenzène sulfonique / leucine-aminopeptidase / minifromage / lactobacille / protéolyse