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Applied and Environmental Microbiology, February 2002, p. 608-615, Vol. 68, No. 2
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.2.608-615.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Conversion of L-Leucine to Isovaleric Acid by Propionibacterium freudenreichii TL 34 and ITGP23

Anne Thierry,1* Marie-Bernadette Maillard,1 and Mireille Yvon2

Laboratoire de Recherches de Technologie Laitière, INRA, 35042 Rennes Cedex,1 Unité de Recherches de Biochimie et Structure des Protéines, INRA, 78352 Jouy-en-Josas Cedex, France2

Received 30 March 2001/ Accepted 14 November 2001

Several branched-chain volatile compounds are involved in the flavor of Swiss cheese. These compounds are probably produced by enzymatic conversion of branched-chain amino acids, but the flora and the pathways involved remain hypothetical. Our aim was to determine the ability of Propionibacterium freudenreichii, which is one of the main components of the secondary flora of Swiss cheese, to produce flavor compounds during leucine catabolism. Cell extracts and resting cells of two strains were incubated in the presence of L-leucine, {alpha}-ketoglutaric acid, and cofactors, and the metabolites produced were determined by high-performance liquid chromatography and gas chromatography. The first step of leucine catabolism was a transamination that produced {alpha}-ketoisocaproic acid, which was enzymatically converted to isovaleric acid. Both reactions were faster at pH 8.0 than at acidic pHs. Cell extracts catalyzed only the transamination step under our experimental conditions. Small amounts of 3-methylbutanol were also produced by resting cells, but neither 3-methylbutanal nor{alpha}-hydroxyisocaproic acid was detected. L-Isoleucine and L-valine were also converted to the corresponding acids and alcohols. Isovaleric acid was produced by both strains during growth in a complex medium, even under conditions simulating Swiss cheese conditions (2.1% NaCl, pH 5.4, 24°C). Our results show that P. frendenreichii could play a significant role in the formation of isovaleric acid during ripening.

* Corresponding author. Mailing address: Laboratoire de Recherches de Technologie Laitière, INRA, 65 rue de Saint-Brieuc, 35042 Rennes Cedex, France. Phone: 33 2 23 48 53 37. Fax: 33 2 23 48 53 50. E-mail: athierry{at}rennes.inra.fr.

Applied and Environmental Microbiology, February 2002, p. 608-615, Vol. 68, No. 2
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.2.608-615.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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