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Applied and Environmental Microbiology, April 2000, p. 1354-1359, Vol. 66, No. 4
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Expression of a Heterologous Glutamate Dehydrogenase Gene in Lactococcus lactis Highly Improves the Conversion of Amino Acids to Aroma Compounds

Liesbeth Rijnen, Pascal Courtin, Jean-Claude Gripon, and Mireille Yvon*

Unité de Recherches de Biochimie et Structure des Protéines INRA, 78352 Jouy-en-Josas Cedex, France

Received 23 September 1999/Accepted 16 January 2000

The first step of amino acid degradation in lactococci is a transamination, which requires an alpha -keto acid as the amino group acceptor. We have previously shown that the level of available alpha -keto acid in semihard cheese is the first limiting factor for conversion of amino acids to aroma compounds, since aroma formation is greatly enhanced by adding alpha -ketoglutarate to cheese curd. In this study we introduced a heterologous catabolic glutamate dehydrogenase (GDH) gene into Lactococcus lactis so that this organism could produce alpha -ketoglutarate from glutamate, which is present at high levels in cheese. Then we evaluated the impact of GDH activity on amino acid conversion in in vitro tests and in a cheese model by using radiolabeled amino acids as tracers. The GDH-producing lactococcal strain degraded amino acids without added alpha -ketoglutarate to the same extent that the wild-type strain degraded amino acids with added alpha -ketoglutarate. Interestingly, the GDH-producing lactococcal strain produced a higher proportion of carboxylic acids, which are major aroma compounds. Our results demonstrated that a GDH-producing lactococcal strain could be used instead of adding alpha -ketoglutarate to improve aroma development in cheese.

* Corresponding author. Mailing address: Unite de Recherches de Biochimie et Structure des Proteines INRA, 78352 Jouy-en-Josas Cedex, France. Phone: 33 1 34 65 21 59. Fax: 33 1 34 65 21 63. E-mail: Mireille.Yvon{at}diamant.jouy.inra.fr.

Applied and Environmental Microbiology, April 2000, p. 1354-1359, Vol. 66, No. 4
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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