Mechanism Of NaNO₂ Inhibiting The Degree Of Oxidation Of Beef And Chicken Myoglobin During Pickling

Livestock and poultry contain a large amount of myoglobin and hemoglobin centered on iron porphyrin,which is easily oxidatively catalyzed with various ligands.According to the research,Na NO₂has positive contribution to the color,flavor,antibacterial and anti-oxidation of processed meat products,but the anti-oxidation mechanism of Na NO₂and myoglobin is still unclear.To study the changes of myoglobin in the whole oxidation process after Na NO₂treatment,this experiment used Simmental hybrid cattle longissimus dorsi and Sanhuang chicken leg as the main research object;using spectrophotometry,Raman spectroscopy and infrared spectroscopy.Means,analyze the free radical content,antioxidant enzyme content and the oxidation index and structure of myoglobin in the process of pickling,reveal the anti-oxidation mechanism of Na NO₂treatment on myoglobin,and marinate the beef chicken.The theoretical basis to produce products and the search for alternatives to Na NO₂.The specific findings and conclusions are as follows:（1）Na NO₂has different effects on different free radicals.The content of O₂^-free radicals and-OH radicals in beef in the experimental group was significantly decreased（P<0.05）,and the content of NO·free radicals was increased（P<0.05）.In chicken meat,the content of NO·free radicals and O2-free radicals decreased.（P<0.05）,the content of-OH radicals increased（P<0.05）.In the control group,the contents of NO·free radicals,O₂^-free radicals and-OH radicals in beef chicken tissues showed a significant upward trend（P<0.05）.With the prolongation of curing time,various free radicals accumulated continuously.Therefore,Na NO₂can cleave or electrophilic reaction with free radicals to scavenge some of the free radicals,and NO₂^-can also participate in the nitration reaction in the body,which increases the formation of some free radicals to some extent.（2）Na NO₂causes oxidative stress on antioxidant enzymes in meat.In the test group,the activity of SOD enzyme increased during the pickling process（P<0.05）,the activity of i NOS enzyme and the activity of GSH-Px decreased（P<0.05）,and the activity of each enzyme in chicken decreased（P<0.05）.In the control group,the activity of SOD in beef tissues decreased（P<0.05）,the activity of i NOS and the activity of GSH-Px increased（P<0.05）,and the results in chicken tissues showed opposite trends（P<0.05）.This is because beef and chicken in the experimental group,the antioxidant enzymes will increase in different degrees in a short period of time,and with the prolongation of stress time,the activated antioxidant enzyme system is not enough to fight the oxidative stress caused by Na NO_2.The enzyme activity will decrease significantly.（3）Na NO₂treatment has an inhibitory effect on the oxidation of myoglobin.In addition to the disulfide bond content and oxygenated myoglobin content in the chicken,all other oxidation indexes were inhibited to varying degrees,especially for the inhibition of high-iron myoglobin content in beef chicken.In the control group,the carbonyl content of myoglobin in beef and chicken was significantly increased（P<0.05）,the content of sulfhydryl group was significantly decreased（P<0.05）,the content of disulfide bond was significantly increased（P<0.05）,and the content of high iron myoglobin was significant.The increase（P<0.05）and the oxygenated muscle red egg content were significantly decreased（P<0.05）.（4）Na NO₂effectively inhibited the change of myoglobin porphyrin ring structure.In the control group,the distance between C atoms in the myoglobin porphyrin ring of beef and chicken became larger（P<0.05）,the C-C bond length increased（P<0.05）,and the overall structure of the porphyrin ring expanded（P<0.05）.The central iron of the porphyrin ring is closer to the plane of the porphyrin ring（P<0.05）.Due to the synergistic effect of steric hindrance and electron orbital level transition,the low-spin Fe²⁺becomes high-spinning Fe³⁺（P<0.05）.At the same time,the content ofα-helix and random coil in the secondary structure decreased（P<0.05）,and the content ofβ-sheet andβ-turn increased（P<0.05）,which caused the myoglobin structure to shrink and tend to be stable.The bending or stretching of the iron ligand,the expansion of the porphyrin ring,the spacing between the central iron and the porphyrin ring,and the changes in the secondary structure were all inhibited in the test group（P<0.05）.Comprehensive analysis showed that Na NO₂treatment inhibited myoglobin oxidation in beef and chicken during pickling.Na NO₂inhibited the expansion of myoglobin porphyrin ring,making Fe closer to the center of porphyrin ring and preventing Fe ligand.The changes that occur further prevent the relaxation of the myoglobin structure and have a positive effect on the maintenance of the color of the meat;at the same time,the anti-oxidase activity also has an inhibitory effect,which requires further study;it has a stabilizing effect on the myoglobin iron porphyrin structure.Meat quality such as flesh color,tenderness and flavor may have a positive effect,but the binding site of Na NO₂to the porphyrin ring needs further study.