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Applied and Environmental Microbiology, July 2004, p. 3855-3861, Vol. 70, No. 7
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.7.3855-3861.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Ability of Thermophilic Lactic Acid Bacteria To Produce Aroma Compounds from Amino Acids

Sandra Helinck,^1, Dominique Le Bars,¹ Daniel Moreau,² and Mireille Yvon^1*

Unité de Recherche de Biochimie et Structure des Protéines, I.N.R.A., 78352 Jouy-en-Josas,¹ Groupe Développement Fromage, Groupe Entremont, 56140 Malestroit, France²

Received 5 March 2004/ Accepted 16 March 2004

Although a large number of key odorants of Swiss-type cheese result from amino acid catabolism, the amino acid catabolic pathways in the bacteria present in these cheeses are not well known. In this study, we compared the in vitro abilities of Lactobacillus delbrueckii subsp. lactis, Lactobacillus helveticus, and Streptococcus thermophilus to produce aroma compounds from three amino acids, leucine, phenylalanine, and methionine, under mid-pH conditions of cheese ripening (pH 5.5), and we investigated the catabolic pathways used by these bacteria. In the three lactic acid bacterial species, amino acid catabolism was initiated by a transamination step, which requires the presence of an -keto acid such as -ketoglutarate (-KG) as the amino group acceptor, and produced -keto acids. Only S. thermophilus exhibited glutamate dehydrogenase activity, which produces -KG from glutamate, and consequently only S. thermophilus was capable of catabolizing amino acids in the reaction medium without -KG addition. In the presence of -KG, lactobacilli produced much more varied aroma compounds such as acids, aldehydes, and alcohols than S. thermophilus, which mainly produced -keto acids and a small amount of hydroxy acids and acids. L. helveticus mainly produced acids from phenylalanine and leucine, while L. delbrueckii subsp. lactis produced larger amounts of alcohols and/or aldehydes. Formation of aldehydes, alcohols, and acids from -keto acids by L. delbrueckii subsp. lactis mainly results from the action of an -keto acid decarboxylase, which produces aldehydes that are then oxidized or reduced to acids or alcohols. In contrast, the enzyme involved in the -keto acid conversion to acids in L. helveticus and S. thermophilus is an -keto acid dehydrogenase that produces acyl coenzymes A.

Present address: Unité Mixte de Recherches Génie et Microbiologie des Procédés Alimentaires, I.N.A.-P.G., 78850 Thiverval-Grignon, France.

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