-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 smallscale (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.

-Diversity of some functional characteristics of melted French Emmental-cheese. Four methods were developed or revised to determine the functionality of melted Emmental-cheese (Swiss-cheese). Flowability was measured using a modified Schreiber test. Stretchability was assessed by a new method involving vertical traction. A butyrometric method was applied to quantify oiling-off. Browning of cheese-gratin was measured objectively with a colour meter (L*, a*, b*). The repeatability and the power of these tests were satisfactory. The functionality of 48 french commercial Emmental-cheeses was determined over one year. Great variations were registered.

Isovaleric acid (3-methylbutyric acid) and 2-methylbutyric acid contribute to Swiss cheese flavour. In order to determine the contribution of propionibacteria (PAB) to the production of methylbutyric acids, mini-Swiss cheeses were manufactured with or without PAB as a secondary starter (25 Propionibacterium freudenreichii strains), associated with different cultures of thermophilic lactic starters. In the presence of PAB, the quantity of methylbutyric acids was three to ten times greater, depending on PAB strain, than in the absence of PAB, regardless of the species and the strain of lactobacilli used (20-63 vs.o6 mg kg À1 ripened cheese). PAB produced methylbutyric acids concomitantly with acetic and propionic acids, then kept on producing methylbutyric acids after propionic fermentation. The increase in salt-in-moisture content of cheese from 1.0% to 1.8% induced a strain-dependent inhibition of isovaleric acid production. This study shows that P. freudenreichii is the main contributor to methylbutyric acid production in Swiss cheese. r

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