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Volume 82, Number 1, January-February 2002
3rd International Symposium on Propionibacteria
Page(s) 17 - 32

Lait 82 (2002) 17-32 DOI: 10.1051/lait:2001002

Production of cheese flavour compounds derived from amino acid catabolism by Propionibacterium freudenreichii

Anne Thierry and Marie-Bernadette Maillard

Laboratoire de Recherches de Technologie Laitière, INRA, 65 rue de Saint-Brieuc, 35042 Rennes Cedex, France

The catabolism of amino acids by cheese micro-organisms results in the production of various volatile flavour compounds. It was recently shown to be a rate-limiting factor in the formation of cheese flavour, leading to an increased interest in elucidating the pathways and the flora involved. This paper reviews the ability of propionibacteria (PAB) to produce flavour compounds deriving from branched-chain, aromatic and sulphur-containing amino acids. In culture media, PAB produced volatile compounds derived from Leu, Ile, Met and Phe. In cheese, the presence of PAB is positively correlated to the amount of acids, alcohols and/or aldehydes derived from Leu or Ile. The metabolic pathways of amino acid conversion to flavour compounds by PAB have been only partly elucidated. Aminotransferase(s) catalyse the first step of conversion of branched-chain, aromatic amino acids and methionine, with a higher activity for branched-chain amino acids. The $\alpha$-keto acids resulting from transamination are further degraded to various compounds by resting cells of PAB. So $\alpha$-ketoisocaproic acid, derived from Leu, is essentially converted to isovaleric acid by a ketoacid dehydrogenase complex; phenylpyruvic acid, derived from Phe, is converted to phenyllactic acid, phenylacetic acid, benzoic acid and benzaldehyde. Methionine can also be directly degraded by $\alpha$, $\gamma$-elimination, leading to methanethiol. The amino acid catabolism pathways in PAB share similarities with those of lactic acid bacteria but PAB seem to produce higher amounts of branched-chain acids, which are important flavour compounds in cheese.

Production de composés d'arôme du fromage issus du catabolisme des acides aminés par Propionibacterium freudenreichii. Le catabolisme des acides aminés par les micro-organismes du fromage entraîne la formation de composés volatils variés. C'est une étape limitante de la formation de la flaveur du fromage, et les recherches visant à déterminer les voies métaboliques et les flores impliquées se sont récemment multipliées. Cette revue fait le point sur le catabolisme des acides aminés en composés d'arôme chez les bactéries propioniques (PAB). Les PAB sont impliquées dans la formation des composés volatils dérivant de Leu, Ile, Phe et Met, par des voies métaboliques qui ne sont que partiellement connues. La première étape de conversion des acides aminés ramifiés, aromatiques et de la méthionine est catalysée par une(des) aminotransférase(s). Les cétoacides résultant de la transamination sont ensuite dégradés en différents composés. Ainsi, l'acide $\alpha$-cétoisocaproïque, issu de Leu, est pour l'essentiel converti en acide isovalérique par un complexe cétoacide déshydrogénase ; l'acide phénylpyruvique, issu de Phe, est converti en acide phényllactique, acide phénylacétique, acide benzoïque et benzaldéhyde. La méthionine peut également être directement dégradée par, $\alpha$, $\gamma$-élimination, formant du méthanethiol. Ces voies cataboliques présentent des similarités avec celles existant chez les bactéries lactiques, mais les PAB produisent plus d'acides ramifiés, qui sont des composés importants dans la flaveur du fromage.

Key words: propionibacteria / flavour compound / amino acid / catabolism / cheese ripening

Mots clés : propionibactéries / composé d'arôme / acide aminé / catabolisme / affinage

Correspondence and reprints: Anne Thierry Tel.: (33) 2 23 48 53 37; fax: (33) 2 23 48 53 50;

© INRA, EDP Sciences 2002

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