*3.8. Residual Nitrite Analysis*

The residual nitrate in meat products can convert to nitrosamine compounds in the human body and cause cancer in the lungs, stomach, esophagus, liver, and bladder [52,53]. Therefore, the residual nitrite content in meat products should be as low as possible. The results of residual nitrite analysis of all groups on days 0, 5, 10, 15, and 20 are shown in Tables 6 and 7. Because the PO was the supplement in the sausage and did not replace the meat in the sausage, the residual nitrite concentrations were not convincing to clarify the true content of nitrite in each group shown in Table 1. To solve this problem, the data in Table 7 were calculated to show the weight of the residual nitrite of each group. With the passage of storage time and increase in PO content, the residual nitrite content of sausage showed a gradually decreasing trend before 15 days. On the 15th day of the storage period, the residual amount of nitrite in the supplement group decreased 24.7~37.35% compared with the control group. After 15 days, the nitrite content in the sausages decreased sharply. On the last day (day 20) of the storage period, the residual amount of nitrite in the supplement group could decrease 45.06~81.97% compared with the control group, which was probably due to the microbial proliferation affecting nitrogen compounds. The low residual nitrite of the supplement group can be explained by the decrease in initial nitrite (day 0). The residual nitrite could react with active substances such as phenolics and terpenes into nitrite acid or nitric oxide. This might be because PO was rich in strong antioxidant activities such as Vitamin C (Vc), which could improve the activity of antioxidant enzymes, interrupt the chain reaction of free radicals, maintain the integrity of cell membrane, and convert methemoglobin to hemoglobin and thereby reduce

the nitrite content [54–58]. In a word, the nitrite residue of sausage with PO was lower than that of the control group over the entire storage period.

**Table 6.** Residual nitrite analysis of *Pleurotus ostreatus* (PO) pork sausages during storage (mg/kg).


a–e Means within the same row with different letters differ significantly among the treatments (*p* < 0.05). Values are given as mean ± standard deviations. Control, PO10, PO20, PO30, and PO40 were 0 wt.%, 10 wt.%, 20 wt.%, 30 wt.%, and 40 wt.% addition of PO puree, respectively.

**Table 7.** Residual nitrite of *Pleurotus ostreatus* (PO) pork sausages during storage for every group (mg).


a–e Means within the same row with different letters differ significantly among the treatments (*p* < 0.05). Values are given as mean ± standard deviations. Control, PO10, PO20, PO30, and PO40 were 0 wt.%, 10 wt.%, 20 wt.%, 30 wt.%, and 40 wt.% addition of PO puree, respectively.
