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 (E-h) 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: E-h 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.