Effect of ascorbate, nitrate and nitrite on the amount of flavour compounds produced from leucine by Staphylococcus xylosus and Staphylococcus carnosus

Resting cells of Staphylococcus xylosus and S. carnosus were incubated with ascorbate, nitrate and nitrite in defined reaction medium and their degradation of H-3-labelled leucine into methyl-branched catabolites were studied using HPLC/radiometric detection. The experiments were carried out with and without addition of alpha-ketoglutarate. The main catabolic product of leucine degradation was 3-methylbutanoic acid but also small amounts of alpha-hydroxy isocaproic acid were produced. Nitrite addition lowered the concentration of 3-methylbutanoic acid for both Staphylococcus species and this effect was strongly amplified by ascorbate for S. xylosus but not for S. carnosus. For both species ascorbate alone had little if any effect. Also nitrate lowered the concentration of 3-methylbutanoic acid for S. xylosus. The concentration of alpha-hydroxy isocaproic acid was, however, increased by addition of nitrite and nitrate for S. xylosus. Addition of alpha-ketoglutarate generally increased the concentration of 3-methylbutanoic acid for both S. xylosus and S. carnosus.