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Cheese flavour is the result of a complex mixture of volatile compounds, originating mainly from the enzymatic degradation of curd components by cheese microflora during cheese ripening. Directing cheese flavour development requires knowledge on inter- and intra-species contributions to flavour development, i.e. identification of the volatile (flavour) compounds produced by each strain. The aim of this study was to identify the volatile compounds produced in Swiss cheese by Propionibacterium freudenreichii, one of the species essential for the development of the characteristic flavour of this type of cheese. The volatile profile of compounds obtained from small-scale (1/100) Swiss cheeses, with or without P. freudenreichii, were compared (three strains tested, in association with three thermophilic lactic starters, i.e. twelve cheeses, manufactured in duplicate). Neutral volatile compounds, extracted by dynamic headspace, and free fatty acids were identified using gas chromatography-mass spectrometry. The concentrations of all carboxylic acids and 14 of 58 neutral compounds were significantly higher in the presence of propionibacteria (PAB). The three PAB strains tested produced the same volatile compounds, but observed quantitative differences were strain-dependent. Propionic acid and four propionate esters were detected only in the presence of PAB. Moreover, cheeses with PAB contained two- to three- fold higher levels of free fatty acids derived from lipolysis and five- to fifty- fold higher levels of branched-chain compounds derived from isoleucine catabolism (2-methylbutanal, 2-methylbutanol and 2-methylbutanoic acid) and from leucine catabolism (3-methylbutanoic acid). Lactic starters induced significant variations in the concentrations of some of the compounds produced by PAB, such as methylbutanoic acids and free fatty acids, which varied by 2.0 and 1.4, respectively, as a function of the lactobacilli strains. PAB strains affect the concentration of varied volatile compounds and could therefore have distinct contributions to the formation of Swiss cheese flavour.Pour maîtriser la formation de la flaveur du fromage, qui est due à une multitude de composés volatils essentiellement produits par la microflore au cours de l'affinage, il est nécessaire de déterminer comment chaque espèce et souche contribue à la formation de composés d'arôme. L'objectif de cette étude était d'identifier les composés volatils produits dans l'emmental par Propionibacterium freudenreichii, une espèce clé du développement de la flaveur caractéristique de ce fromage. Douze mini-emmentals (échelle 1/100) ont été fabriqués en double, en associant P. freudenreichii (trois souches) et un témoin sans propionibactéries, à trois levains lactiques. Les composés volatils neutres de ces fromages et les acides gras libres ont été analysés par chromatographie en phase gazeuse. Seuls les fromages ensemencés en propionibactéries contenaient de l'acide propionique et quatre esters de propionate. Ces fromages contenaient également 2 à 3 fois plus d'acides gras libres et 5 à 50 fois plus de composés ramifiés volatils issus du catabolisme de l'isoleucine (2-méthylbutanal, 2-méthylbutanol et acide 2-méthylbutanoïque) et de la leucine (acide 3-méthylbutanoïque), avec des différences très significatives selon les souches. Les lactobacilles associés modulaient les concentrations de certains composés produits par P. freudenreichi (acides méthylbutanoïques et acides gras libres). Les souches de P. freudenreichi, en faisant varier la concentration de divers composés volatils, pourraient avoir des contributions distinctes à la formation de la flaveur de l'emmental

Propionibacterium freudenreichii strains quantitatively affect production of volatile compounds in Swiss cheese