Coagulase-negative staphylococci enhance the colour of fermented meat through a complex cross-talk between the arginase and nitric oxide synthase activities

The nitric oxide synthase (NOS) activity was investigated in 35 staphylococcal strains from five distinct coagulase-negative staphylococci (CNS) species. NOS pathway is related with the production of nitric oxide, potentially leading to the formation of nitrosomyoglobin imparting a pinkish-red colour to fermented meats. NOS activity was investigated employing both genotypic and phenotypic methods. Among the strains studied, 16 were found to contain the gene encoding NOS, while 25 strains possessed the arginase gene. Strains from Staphylococcus saprophyticus, S. equorum, and S. carnosus species exhibited phenotypic NOS-like activity. This was evidenced by the production of L-citrulline and a comparably lower release of L-ornithine in meat simulation media fermented under microaerobic conditions by those staphylococcal cultures. The authentic NOS activity was further examined using lab-scale meat models. The characteristic red colouration, typically associated with sodium nitrite-cured meat products, was observed. Strains L31, L49, and V10 (S. saprophyticus) demonstrated a pronounced effect on meat colouration, achieving shades comparable to nitrite-enhanced meat; however, a concurring up-accumulation of putrescine and spermine (likely originating from ornithine) was also outlined. These findings suggest the potential of meat-associated CNS to promote colour development in nitrite-free meats, offering a promising area for enhancing the visual appeal of such products.