Addition of oxidizing or reducing agents to the reaction medium influences amino acid conversion to aroma compounds by Lactococcus lactis.

AIMS: The aim of this research was to investigate the impact of extracellular redox potential (Eh) on amino acid conversion to aroma compounds by Lactococcus lactis that is commonly used as a starter in the cheese industry. METHODS AND
RESULTS: The study was realized in vitro by incubating resting cells of L. lactis in reaction media in which E(h) was modified by the addition of oxidizing or reducing agents. Oxidative condition (+300 mV) favoured the production of aldehydes and volatile sulfur compounds responsible for malty, floral, fruity, almond and cabbage aroma. This production was mainly the result of a chemical oxidation of the alpha-keto acids produced by amino acid transamination. In contrast, reducing condition (-200 mV) stimulated the production of carboxylic acids such as phenylacetic, methylthiopropionic and isovaleric acids, which contribute to the very-ripened-cheese aroma as well as the production of hydroxy acids.
CONCLUSIONS: Eh of the medium highly influences the nature of aroma compounds produced from amino acid catabolism by the resting cells of L. lactis. SIGNIFICANCE AND IMPACT OF THE STUDY: E(h) is a parameter that is not controlled during cheese production. Its control throughout cheese making and ripening could permit control of aroma formation in cheese.