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Identification and characterization of glutamate dehydrogenase activity in wild Lactococcus lactis isolated from raw milk cheeses

Gómez de Cadiñanos, Luz P., Peláez, Carmen, Martínez-Cuesta, M.Carmen, García-Cayuela, Tomás, Requena, Teresa
European food research & technology 2018 v.244 no.4 pp. 603-609
Lactococcus lactis, alpha-ketoglutaric acid, cheese ripening, cheeses, enzyme activity, flavor, food research, genes, genomics, glutamate dehydrogenase, glutamic acid, plasmids, polymerase chain reaction, raw milk, transamination
The glutamate dehydrogenase (GDH) catalyses the reversible conversion of glutamate into α-ketoglutarate, which initiates amino acid transamination during cheese ripening. This work has investigated the GDH activity in 39 wild isolates of Lactococcus lactis from raw milk cheeses. Only 25% of the isolates were GDH positive with NAD⁺ as the preferred cofactor. L. lactis IFPL953 showed the highest NAD-GDH activity. The GDH activity at the genetic level in the lactococcal isolates was analysed by PCR amplification of the gdh gene in genomic and plasmid DNA. The gdh gene arrangement of L. lactis IFPL953 in its plasmid location was similar to that in the reference strain GDH⁺ L. lactis TiL504, suggesting that both lactococci could harbour the same plasmid pGdh442 containing the gdh gene. L. lactis IFPL953 has previously demonstrated a remarkable α-ketoisovalerate decarboxylase activity, which along with its high GDH activity makes the strain particularly useful in enhancing cheese flavour formation.