Evaluation of nitrosylmyoglobin production in autochthonous microorganisms isolated from Yunnan traditional fermented meats: Focus on coagulase-negative cocci

Color-enhancing starter cultures can serve as substitutes for nitrites in meat products. Therefore, in this study, eighteen autochthonous microorganisms isolated from Yunnan fermented meats were screened for their ability to produce red coloration in a metmyoglobin model system. Subsequently, four coagulase-negative cocci — Kocuria rhizophila, Mammaliicoccus vitulinus, Kocuria salsicia, and Staphylococcus epidermidis — were selected. Western blot and NO production assays demonstrated the nitric oxide synthase (NOS) activity of these microorganisms. Their color-promoting effects were further validated based on pentacoordinate nitrosylmyoglobin production. Notably, the microbes were found to alter the oxidation states of myoglobin, promoting color generation in meat products. K. rhizophila, which showed the strongest NOS activity (0.83 ± 0.02 U/mL, P < 0.05), produced the highest amount of nitrosylmyoglobin (22.31 ± 0.71 ppm, P < 0.05) and generated the highest level of redness (10.38 ± 0.55, P < 0.05) after 7 days of fermentation. In contrast, the uninoculated control group showed a nitrosylmyoglobin concentration and redness value of 16.67 ± 0.71 ppm and 7.33 ± 0.47, respectively. This study is the first to detect NOS expression in Kocuria spp. and demonstrate the ability of these microbes to generate nitrosylmyoglobin in situ, expanding the range of potential starter cultures available for enhancing the color of meat products.