Pyruvate stimulates transamination of leucine into α-ketoisocaproic acid and supports 3-methylbutanal production by Lactococcus lactis.

AIM

To investigate the effect of pyruvate and glucose on leucine transamination and 3-methylbutanal production by Lactococcus lactis, including the comparison with cells possessing glutamate dehydrogenase (GDH) activity.

METHODS AND RESULTS

Lactococcus lactis cells were incubated in chemically defined medium (CDM) with the pH controlled at 5.2 to mimic cheese conditions. Pyruvate supplementation stimulated the production of the key flavour compound 3-methylbutanal by 3-4 times after 72 h of incubation. Concurrently, alanine production increased, demonstrating the involvement of pyruvate in transamination reactions. Glucose-metabolizing cells excreted α-ketoisocaproic acid and produced even 3 times more 3-methylbutanal after 24 h than pyruvate-supplemented cells. Conjugal transfer technique was used to transfer the plasmid pGdh442 carrying the gdh gene encoding for GDH to L. lactis. Introducing GDH did not stimulate the excretion of α-ketoisocaproic acid and the production of 3-methylbutanal.

CONCLUSIONS

These results demonstrate that Lactococcus uses pyruvate to transaminate leucine into α-ketoisocaproic acid which supports 3-methylbutanal production. Surprisingly, GDH activity did not stimulate leucine transamination and 3-methylbutanal production.