Screening and optimization of a nitrate reductase-producing Staphylococcus simulans UV-11 and its application

A strain of Staphylococcus simulans D14 (S. simulans D14) showed the highest nitrate reductase activity (NRA) of 4.52 mM NO(2)(−)/mg dry weight by the spectrophotometric method, which was screened from traditional Chinese sausage. When the UV mutagenesis time was 25 s, the positive mutation rate was the highest at 26.60%. The NRA of the obtained positive mutant UV-11 was 9.21 mM NO(2)(−)/mg dry weight, and the activity was found to be 1.04-fold higher than that of the original strain S. simulans D14. A Plackett–Burman design (PBD) was employed to screen the significant variables pH, KNO(3) (%) and incubation time (h), and response surface methodology (RSM) was used to optimize the significant variables using a Box–Behnken design (BBD). The results showed that the NRA of S. simulans UV-11 was 15.22 mM NO(2)(−)/mg dry weight under optimum conditions of 37 °C, pH 6.5, incubation time 15 h, KNO(3) 0.045%, NaCl 5%, NaNO(2) 0.015%, peptone 1%, and D–mannitol 1%, which increased by 65.2% compared with the unoptimized medium. Natural curing agents (containing 10(7) CFU/g S. simulans UV-11 under optimal conditions and 1.40% celery powder, T2) were added to the cured meat model. T2 produced significantly lighter and redder signals than the control group (C) and the addition of 150 ppm NaNO(2) group (T1). The thiobarbituric acid reactive substance (TBARS) of T2 was 2.30 mg malonaldehyde/kg product and residual nitrite of T2 was 7.1 ppm after 14 days of storage,which were lower than those groups of C and T1. Taking into account the results of cured meat models, S. simulans UV-11 could be selected as a potential starter culture for the processing of natural meat products.