Study On The Effect Of Gynura Bicolor (Roxb.ex Willd.) DC.Extract On The Quality Of Minced Rabbit Meat And The Inhibition Of Protein Oxidation

Rabbit meat has high nutritional quality.However,the content of unsaturated fatty acids and protein in rabbit meat is relatively high.Therefore,the oxidation of fat and protein in rabbit meat is easily formed in the process of refrigeration and processing,which affects the eating quality and processing characteristics of rabbit meat.Chemically synthesized preservative has potential toxicity,and it will cause certain harm to human health when it is eaten for a long time.Natural preservative has broad prospects due to its characteristics of green,safe,wide-source and high-efficiency,and it has received a lot of attention around the world.Gynura bicolor（Roxb.ex Willd.）DC.is rich in polyphenols,flavonoids,carotenoids,anthocyanins,having the characteristics of anti-inflammatory activity,antioxidant activity,and anti-hyperglycemic functions,which makes it possible to become a kind of natural preservative.However,there has been very little research on Gynura bicolor,especially the research on the utilization of Gynura bicolor in the field of meat preservation as a kind of natural preservative.Based on these,the ultrasonic-assisted extraction process of Gynura bicolor extract was optimized.And the two optimization methods,response surface methodology（RSM）and back propagation artificial neural network（BP-ANN）were compared.Next,the antioxidant capacity of the extract from Gynura bicolor was determined.Then the effect of Gynura bicolor extract on the preservation of minced rabbit meat at 4℃was studied.UPLC-QTOF-MS was used to analyze the main phenolic substances in the extract of Gynura bicolor.Finally,the effects of the main phenolic substances in Gynura bicolor on the physicochemical properties and structure of oxidized myofibrillar protein（MP）induced by hydroxyl radical were studied.It can provide a certain reference for Gynura bicolor as a kind of natural preservative to play an increasingly significant role in keeping the quality of rabbit meat.The main contents and conclusions of the research are as follows:（1）The ultrasonic-assisted extraction of Gynura bicolor extract was optimized,and the two optimization methods of RSM and BP-ANN were compared.The antioxidant capacity of the extract from Gynura bicolor was determined by measuring the scavenging ability of DPPH free radicals,ABTS free radicals,and hydroxyl free radicals as well as measuring the chelating ability of Fe²⁺and total reducing capacity.The results showed that the optimal process parameters obtained by RSM were as follows:extraction temperature 72℃,ethanol concentration 63%,ultrasonic time 2.5 h,ultrasonic power187 W.Under these conditions,the predicted flavonoid content was 7.67 mg/g,and the verified test showed that the flavonoid content of the extract was 7.32 mg/g.The relative error between the real value and the predicted value was 4.78%.The optimal extraction parameters obtained by BP-ANN were as follows:extraction temperature 69℃,ethanol concentration 60%,ultrasonic time 2.6 h,ultrasonic power 199 W.Under these conditions,the predicted flavonoid content was 7.74 mg/g,and the verified test showed that the flavonoid content of the extract was 7.65 mg/g.The relative error between the real value and the predicted value was 1.18%.It is found that the prediction model based on BP-ANN is an effective optimization method through comparison and verification.Compared with response surface method,BP-ANN has better prediction effect and smaller relative error.The antioxidation evaluation of the obtained extract of Gynura bicolor showed that the IC₅₀ value of DPPH free radical scavenging rate,ABTS free radical scavenging rate,Fe²⁺chelating ability,hydroxyl radical scavenging rate were 4.83,6.37,10.0,9.82 mg/m L,respectively.The result showed that the Gynura bicolor extract had certain scavenging ability of DPPH free radicals,ABTS free radicals,and hydroxyl free radicals.It also had certain chelating ability of Fe²⁺.The extract of Gynura bicolor has great potential as a kind of natural antioxidant.（2）The effect of extract of Gynura bicolor on the preservation of minced rabbit meat at 4℃during 12 days was studied.The results showed that the Gynura bicolor extract can effectively inhibit the lipid oxidation of minced rabbit meat and it can inhibit the formation of peroxide and malondialdehyde.It can also inhibit the oxidation of protein,and inhibit the increase of carbonyl content and the decrease of sulfhydryl content in minced rabbit meat during the chilled storage time.The extract of Gynura bicolor had antibacterial effect.It can effectively delay the increase of p H and the total number of colonies of minced rabbit meat.In addition,the Gynura bicolor extract can reduce the cooking loss,slow down the increase of the hardness of minced rabbit meat and improve the color stability.The Gynura bicolor extract can also inhibit the sensory deterioration of minced rabbit meat during the storage time.In terms of overall acceptance,the scores of the groups added Gynura bicolor extract were higher than that of the control group starting from the 4th day.And the scores of the group added Gynura bicolor extract were slightly higher than the group added BHT during the later storage period.（3）UPLC-QTOF-MS was used to analyze the main phenolic substances in the extract of Gynura bicolor.The effects of the main phenolic substances in the extract of Gynura bicolor on the physicochemical properties and structure of oxidized myofibrillar protein induced by hydroxyl radical were studied.The results showed that the main phenolic substances in the extract of Gynura bicolor were quercetin,rutin,rosmarinic acid,ellagic acid and dihydromyricetin according to UPLC-QTOF-MS analysis.These five substances can effectively inhibit the formation of carbonyl groups and the decrease of sulfhydryl and free amino groups.These five substances can also effectively reduce the degree of transformation ofα-helix to random coils in MP.In addition,the five main phenolic substances can effectively inhibit the oxidative damage of myosin and actin caused by hydroxyl free radicals and maintaining the thermal stability of MP.They can also inhibit the oxidative damage to aromatic amino acids induced by hydroxyl radicals,and inhibit the decrease of endogenous fluorescence intensity.At the same time,these five substances can inhibit the increase of the surface hydrophobicity of MP and the decrease of solubility.They can also inhibit the cross-linking and aggregation of MP caused by hydroxyl radical-induced oxidation.