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

Abstract

-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 α-keto acids resulting from transamination are further degraded to various compounds by resting cells of PAB. So α-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 α, γ -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.propionibacteria / flavour compound / amino acid / catabolism / cheese ripening Résumé -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 résul-tant de la transamination sont ensuite dégradés en différents composés. Ainsi, l'acide α-cétoisoca-proïque, 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 α, γ -élimination, formant du méthanethiol. Ces voies cataboliques présentent des si...

The role of propionibacteria in the volatile profile of Pategrás cheeses

“…In fact, data from literature revealed that the degree in which PAB can influence the sensory characteristics of cheeses is highly dependent on cheese composition (mainly NaCl content) and ripening temperature. For example, PAB had a lesser effect on the volatile profile of Morbier cheese than that of Swiss cheese (Thierry and Maillard 2002).…”

“…3-Methyl-1-butanol, which is presumably originated from leucine, was the second most abundant alcohol in the majority of samples. This compound has a pleasant aroma of fresh cheese (Curioni and Bosset 2002), and it has been detected at substantial levels in cheeses containing PAB (Engels et al 1997;Thierry and Maillard 2002;Thierry et al 2004aThierry et al , 2005a. Methyl ketones (from C 3 to C 11 ), 2,3-butanedione (or diacetyl), and 3- hydroxy 2-butanone (or acetoin) were the main ketones identified in Pategrás cheeses.…”

“…However, this ability has been shown to be highly strain dependent. This would explain the fact that 3-methyl-1-butanol was found at significantly greater levels in some cheeses made with PAB (Thierry and Maillard 2002;Thierry et al 2005a), while in other cheeses, its concentration was not affected by the presence of these microorganisms (Thierry et al 2005b). …”

“…In Gruyère and Maasdam cheeses, aldehydes were identified as important components of water-soluble fraction (Engels et al 1997). In particular, branched-chain aldehydes are considered as characteristic compounds of cheeses made with PAB (Thierry and Maillard 2002;Thierry et al 2004aThierry et al , 2005a. On the other hand, ethyl esters were the main esters in Pategrás cheeses.…”

“…Its level decreased in both types of cheeses, but this decrease was more pronounced in cheeses R. At the end of ripening, cheeses with added PAB reached values significantly higher in comparison to the reference cheeses (P < 0.05). P. freudenreichii has demonstrated the ability to produce various aromatic compounds from phenylalanine in in vitro assays (Thierry and Maillard 2002). However, studies carried out in cheeses indicated that benzaldehyde production was not significantly affected by PAB (Thierry et al 1999).…”