Effects Of Malondialdehyde Oxidative Stress On Emulsifying And Gelling Properties Of Pork Myofibrillar Protein

Meat products are rich in lipids and proteins.Lipid peroxidation products further promote protein oxidation,leading to a decline in the quality of meat and meat products.Natural antioxidant polyphenols are often used in meat processing to delay protein oxidation.An in-depth understanding of the effects of lipid peroxidation products and polyphenols on myofibrillar proteins is essential for regulating the quality of meat products.This study investigated the effect of(-)-epigallocatechin-3-gallate(EGCG)on the conformation and gel properties of myofibrillar protein(MP)under malondialdehyde(MDA)-induced oxidative stress.The protein carbonyl,free amine group,thiol content,protein solubility,surface hydrophobicity and tryptophan fluorescence intensity were analyzed for clarifying the changes in protein physicochemical properties and structural properties.Measuring the gel strength,water holding capacity(WHC)and rheological properties,and observing the microstructure of the gel to characterize the structural and functional properties of the MP emulsion gel and the thermally induced gel.The specific test contents and results are as follows:(1)In the MP heat-induced gel system,as the concentration of MDA(6-24 mM)increases,the physicochemical properties,structural properties and gel properties of the MP were deteriorated.The effect of EGCG on MP and gel quality depended on the concentration of MDA.At the low concentration of MDA(6 mM),the addition of EGCG resulted in further loss of MP free amine and sulfhydryl groups,severe MP aggregation,and a significant decrease in the WHC and gel strength.At the high concentration of MDA(12 mM),the addition of EGCG significantly inhibited the damage of MP tertiary structure,increased the content of MP free amine and sulfhydryl groups,improved the gel structure network,alleviated the gel strength and improved the WHC of the heat-induced gel.When excess MDA(24 mM)was added,the addition of EGCG led to a further decrease in the content of MP thiol,a breakdown of the tertiary structure,and a decrease in the gel strength of the MP gel.And more protein aggregates on the gel surface could be observed.(2)In the MP emulsion gel system,at the low concentrations of MDA(3 or 6 mM),the physicochemical and structural properties of MP decreased,but the emulsifying ability of the MP and the elastic modulus of the emulsion gel were improved.The addition of EGCG caused a further decrease in the physicochemical properties,structural properties and emulsifying ability.Simultaneously,the WHC,gel strength and elastic modulus of the emulsion gel decreased remarkably.At the high concentration of MDA(12 mM),the physicochemical and structural properties of MP were severely damaged,the "oil leakage" of the emulsion gel was observed,and the WHC was significantly reduced.With the addition of EGCG,the physicochemical properties,structural properties and emulsifying properties of the MP were improved,the "oil leakage" of the emulsion gel was suppressed,the gel strength and storage modulus were alleviated,and the WHC of the emulsion gel was improved.Malondialdehyde can directly induce the oxidation of myofibrillar proteins,resulting in changes in the physicochemical and structural properties of the protein,emulsifying and gelling properties.EGCG can effectively bind MDA and reduce the oxidative stress on MP,but it can also covalently crosslink with MP,which will affects the functional properties of MP.