Protective Mechanism Of Alcohol Extract Of Houttuynia Cordata Polyphenol Against Linleic Acid Oxidation-induced Protein Damage In Dazu Black Goat Meat

Dazu black goat is one of the most popular goat breeds in southwest China.It is rich in protein and unsaturated fatty acids,has good nutritional properties.However,in the process of transportation,storage,processing and sales,myofibrillar protein is easily attacked by lipid oxidation products,which changes the water-holding capacity of meat products,thereby affecting the edible quality of meat products.Therefore,analyzing the oxidative modification effect and initiation mechanism of lipid oxidation on Dazu black goat meat protein is a necessary condition for the development of precise regulation technology of Dazu black goat meat protein oxidation.Houttuynia cordata is a unique natural plant resource in Southwest China.It is rich in chlorogenic acid,flavonoids,quercetin and other antioxidant components,and has a good antioxidant effect.However,there are few reports on the effects of Houttuynia cordata polyphenol extracts on the meat products.Based on,this paper used linoleic acid to construct a lipid reactive oxygen system to study the oxidative modification effect of lipid oxidation on the myofibrillar protein of Dazu black goat meat;and then,to explore the regulatory effect of Houttuynia cordata polyphenol extract treatment on the oxidation and functional properties of myofibrillar protein;Finally,the inhibitory effect of Houttuynia cordata polyphenols extract on lipid and myofibrillar protein oxidation in complex meat system was discussed,and the reason for the change of the water-holding capacity of myofibrillar protein gel was further analyzed under oxidative conditions..The main conclusions are as follows:(1)The effects of different concentrations of linoleic acid(0-20 mmol/L linoleic acid,3750 unit lipoxygenase/m L)on the changes of charge level and structure caused by oxidative modification of Dazu black goat myofibrillar protein were discussed.The results showed that with the increase of linoleic acid concentration,the oxidation intensified and the sulfhydryl content decreased significantly(p < 0.05),which in turn led to the transformation between the secondary structures of myofibrillar proteins.Among them,the α-helix is destroyed,random coils are generated,and the structure of myofibrillar protein tends to be unstable.After oxidation,the content of charged amino acids decreased,the positive charge decreased,and the carbonyl content increased significantly(p < 0.05),so the net negative charge in myofibrillar protein increased with oxidation,and the hydration effect was enhanced.Under the condition of lowconcentration oxidation(< 10 mmol/L),the promoting factor dominates,and the increase of the net negative charge enhances the interaction between protein and water,which helps to improve the water-holding capacity of meat protein;Under the condition of high concentration of oxidation(> 10 mmol/L),inhibitory factors dominated,and protein cross-linking and aggregation caused by dramatic changes in protein structure reduced the water-holding capacity of myofibrillar proteins.The effects of different concentrations of Houttuynia cordata polyphenol extracts(0-100 μg/m L Houttuynia cordata polyphenol extract,15 mmol/L linoleic acid,3750 unit lipoxygenase/m L)on the oxidation and water-holding capacity of Dazu black goat myofibrillar protein were investigated.The results showed that with the increase of antioxidants,the free radical scavenging rate of myofibrillar protein was significantly increased,and the carbonyl content was greatly decreased(p < 0.05),showing an obvious dose-dependent;The thiol content,amino acid content,surface hydrophobicity and endogenous fluorescence intensity decreased significantly(p < 0.05).At low concentrations of antioxidants(< 60 μg/m L),Houttuynia cordata polyphenol extract significantly inhibited the reduction of α-helix caused by oxidation and promoted the cross-linking of protein molecules,which was manifested as higher thermal stability and improved water-holding capacity.At higher concentrations of antioxidants(> 60 μg/m L),the protein is over-expanded,the α-helix disintegrates into β-sheets,and disordered aggregation and cross-linking are formed,resulting in reduced thermal stability and water-holding capacity.The reasons for the effect of Houttuynia cordata polyphenolic extract(0-80 μg/m L Houttuynia cordata polyphenol extract,5,15 mmol/L linoleic acid,3750 unit lipoxygenase/m L)on the gel properties and water-holding capacity of Dazu black goat muscle myofibrillar protein were discussed.The strong antioxidant properties of Houttuynia cordata polyphenol extracts can reduce the formation of lipid secondary products malondialdehyde and carbonyl derivatives(p < 0.05)to reduce the adverse effects of oxidation on myofibrillar protein gel.An appropriate amount of Houttuynia cordata polyphenol extract(< 60 μg/m L)helps the myofibrillar protein composite gel to form a compact and ordered three-dimensional network structure,and improves the overall water content in the gel,among them,the content of bound water and less mobile water is higher,which improves the water-holding capacity of the gel.Excessive Houttuynia cordata polyphenol extract(> 60 μg/m L)will hinder the orderly interaction between proteins,which is not conducive to the formation of three-dimensional gel network,this leads to uneven distribution of water channels in the gel,a large amount of bound water and less mobile water are converted into free water,the cooking loss rate increases and the water-holding capacity decreases.