Expression of a heterologous glutamate dehydrogenase gene in Lactococcus lactis highly improves the conversion of amino acids to aroma compounds.
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.
Rijnen
L
L
Unité de Recherches de Biochimie et Structure des Protéines INRA, 78352 Jouy-en-Josas Cedex, France.
Courtin
P
P
Gripon
J C
JC
Yvon
M
M
D000596:Amino Acids / Q000378:metabolism*; D002611:Cheese / Q000382:microbiology; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D005969:Glutamate Dehydrogenase / Q000235:genetics* / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007656:Ketoglutaric Acids / Q000378:metabolism; D013294:Lactococcus lactis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D010462:Peptostreptococcus / Q000201:enzymology* / Q000235:genetics; D010957:Plasmids; D014169:Transformation, Bacterial
D000596:Amino Acids; D007656:Ketoglutaric Acids; D005969:Glutamate Dehydrogenase