Effects And Mechanism Of Oxidative Modification Of Beef Protein Induced By Lipid-Oxidizing System

Beef is rich in nutritional value,which is the source of livestock and poultry meat favored by consumers.High protein is an important characteristic of beef,which is closely related to texture,water holding capacity and other quality characteristics.In recent years,protein oxidation has become a hot spot in the field of meat science research,and it has also attracted the attention of the international community in the aspects of affecting the properties and characteristics of Meat products.In complex meat systems,lipid oxidation is usually upstream of the oxidation cascade.Therefore,protein is easy to be exposed to the stress of lipid oxidation.A variety of reactive oxygen species formed by lipid oxidation can induce the oxidation of muscle protein.In the composition of beef protein,sarcoplasmic protein and myofibrillar protein account for more than 95% of the total content,which are easy to be induced by lipid derived reactive oxygen species to produce protein oxidation reaction,and then cause changes in beef quality.As a new processing technology,protein oxidation regulation has become the focus of people’s attention.It is necessary to analyze the initiating effect and mechanism of lipid activated oxidation system on oxidative modification of beef protein to develop precise regulation technology of protein oxidation.However,few studies have reported the oxidative stress effect and mechanism of lipid oxidation on beef protein.Based on this,a lipid oxidation simulation system was constructed with linoleic acid to study the oxidative modification effect of lipid oxidation on beef myofibrillar protein and sarcoplasmic protein.Meanwhile,the potential mechanism of lipid oxidation induced protein oxidation was studied in a complex meat simulation system.The purpose of this paper is to explore the effect and mechanism of lipid oxidation on the oxidative modification of beef protein,so as to provide theoretical basis for the precise regulation of beef protein oxidation.The specific conclusions are as follows:(1)The mechanism of linoleic acid oxidation system(0-10 mmol/L linoleic acid,3750 unit lipoxygenase/m L)to induce the heat preservation gel of beef myofibrillar protein was studied.With the increase of the concentration of linoleic acid,the total sulfhydryl content of myofibrillar protein decreased significantly(p < 0.05),accompanied by the decrease of the maximum absorption peak intensity of intrinsic fluorescence spectrum and ultraviolet absorption spectrum(p < 0.05),indicating that the lipo excitation system led to the unfolding and cross-linking of beef myofibrillar protein.Moderate concentration of linoleic acid(≤ 6 mmol/L)significantly increased the water holding capacity of the gel,while the relative high linoleic acid concentration(> 6 mmol/L)decreased the gel water holding capacity.When the concentration of oxidized linoleic acid increased from 0 to 10 mmol/L,it was not easy for mobile water to drop from92.91% to 78.97%,and free water increased from 6.13% to 19.80%.This result showed that no matter the concentration of linoleic acid,it would have adverse effects on gel water holding capacity.However,moderate concentration of linoleic acid(≤ 6 mmol/L)can lead to the transfer of α-helixes to β-sheets in myofibrillar protein gel,and has a positive effect on the water holding capacity of gels.Protein unfolding and cross-linking together determine the water holding capacity of the gel when the medium concentration of oxidized linoleic acid is treated.However,at higher concentration of oxidized linoleic acid,the aggregation of the protein leads to a decrease in the water holding capacity of the gel.(2)The mechanism of oxidative aggregation of beef sarcoplasmic protein under the stimulation of lipid reactive oxygen species was studied(0-10 mmol/L oxidized linoleic acid,3750 unit lipoxygenase/m L).With the increase of linoleic acid concentration,the relative content and carbonyl content of metmyoglobin increased significantly(p <0.05),while the total sulfhydryl content and solubility decreased significantly(p < 0.05).The results of intrinsic fluorescence spectrum and surface hydrophobicity showed that linoleic acid could induce the unfolding and hydrophobic group exposure of sarcoplasmic protein.The results of SDS-PAGE showed that linoleic acid could cause disulfide cross-linking of sarcoplasmic protein.in addition,with the increase of the concentration of linoleic acid,the turbidity of sarcoplasmic protein increased gradually,which indicated that linoleic acid could induce the aggregation of sarcoplasmic protein.Hydrophobic interaction and protein disulfide cross-linking are the main forces of linoleic acid stress on sarcoplasmic protein aggregation.Oxidation leads to the heterogeneous aggregation of sarcoplasmic proteins.(3)In this paper,the oxidation and degradation of myoglobin in complex meat system under the action of lipoxygenation system were studied,and the mechanism of myoglobin oxidation mediated by lipoxygenation system was discussed.With the increase of the concentration of linoleic acid,the content of lipid hydroperoxide and malondialdehyde increased significantly(p < 0.05),indicating that the content of reactive oxygen species increased in the system.With the increase of the concentration of linoleic acid,the content of protein carbonyl compounds increased significantly,while the content of sulfhydryl group decreased significantly.Meanwhile,the content of metmyoglobin,ferrylmyoglobin and hydroxyl free radical increased significantly(p <0.05).The absorption peak of shore band shows a trend of decrease and blue shift.The oxidation of sarcoplasmic protein and myofibrillar protein directly induced by lipoxygenation system is only one way of oxidative modification.Lipid reactive oxygen species system can also mediate myoglobin reactive oxygen species system and metal reactive oxygen species system,which also plays a role in inducing oxidative modification of beef sarcoplasmic protein and myofibrillar protein.