Effect of NOS-YkuN-YumC on the colour of pork at different postmortem times

This study investigated the effect of NOS-YkuN-YumC, a fusion enzyme of nitric oxide synthase (NOS), on the colour of pork at different postmortem times (0, 5 d) at 10°C and 25°C. The results showed that in the presence of NOS-YkuN-YumC, more nitrosomyoglobin (NO-Mb) was formed in the pork at day 0 postmortem compared to that at day 5 postmortem (P < 0.05). This also led to a higher a*-value (redness) in the pork at day 0 postmortem (P < 0.05). The reduced nicotinamide adenine dinucleotide phosphate (NADPH) content in the pork samples decreased with postmortem time (P < 0.05), and the pork at day 0 postmortem exhibited the highest pH value (P < 0.05). These may be responsible for the differences in the NO-Mb content and a*-value between pork samples at different postmortem times, as NADPH and a neutral pH are required for NOS-YkuN-YumC. Additionally, it was found that colour formation can be enhanced by the fusion enzyme at 10°C, albeit with a longer time requirement. This study provides a theoretical basis for the application of NOS-YkuN-YumC for colour formation in meat at different postmortem times.