Interactions Between Lipid Oxidation Products And Proteins During Storage And Their Effects On Storage Quality In Peanuts

Peanuts are an important source of vegetable lipid and protein.They are rich in polyunsaturated fatty acids,and they are susceptible to oxidation,rancidity and deterioration affected by many factors(such as temperature,relative humidity,oxygen concentration,light,packaging materials,etc.)during storage or processing.The resulting lipid free radicals,peroxides and primary/secondary oxidation products may induce changes in protein space structure.Thus,it is extremely important to study the lipid oxidation pattern,protein quality changes and their interaction mechanisms of peanuts during storage to improve the storage quality of peanuts and reduce the loss of oil resources.In this paper,the lipid oxidation and protein structure changes of different types of peanuts(high oleic acid content,common oleic acid content)stored for 180 d at different temperatures(15,25,35 ℃)were studied.Based on isotope labeling relative and absolute quantification(i TRAQ)technology,the most important biochemical metabolic pathways involved in storage peanut protein were determined.On this basis,an oxidation system was established to simulate the lipid oxidation product-protein oxidation interaction during peanut storage,and the mechanism of quality deterioration of stored peanuts was further clarified.The contents of the research discussion are as follows:(1)The lipid quality changes of two types of peanuts stored at different temperatures for180 days were studied.The results showed that the lipid oxidation degree of the two types of peanuts was increased with the increase of storage temperature and the extension of time.The peroxide value,malondialdehyde content and fatty acid value increased significantly,and peanuts had the high lipid oxidation stability at low temperature(15 ℃)storage.The composition and content of fatty acids in peanuts changed to different degrees.Among them,the changes of oleic acid and linoleic acid were the most obvious.The ratio of oleic acid/linoleic acid(O/L)in peanuts increased significantly,and the O/L value of normal peanuts were lower than that of high oleic peanuts during the whole storage period.In addition,high oleic acid peanuts were stable,and their lipid oxidation stability was higher than that of common peanuts.(2)The protein quality of two types of peanuts stored at different temperatures for 180 days was studied.The results showed that the content of total protein,essential,total and antioxidation amino acids in high-oleic peanuts were higher than those in normal peanuts affected by the storage environment.Affected by the storage environment,some amino acids changed significantly after storage at high temperature(35 ℃).With the increase of storage temperature and the extension of time,the content of free sulfhydryl content of two types peanut protein decreased,and the protein oxidation value increased,and the content of α-helix and β-sheet decreased significantly,and the random coil was increased significantly,and the particle size and surface hydrophobicity increased.In addition,the surface microstructure of the two types of peanuts changed after storage at 35 ℃.These results revealed that higher temperature storage had a significant effect on peanut protein structure,and the protein quality stability of high-oleic acid peanuts was higher than that of normal peanuts.(3)The differentially expressed proteins of two types peanut were identified and quantified before and after storage.Combined with gene ontology(GO)and Kyoto Encyclopedia of Genes and Genomes(KEGG),the mechanism of peanut quality deterioration and the inherent difference between the two types of peanuts were discussed.The study found that a total of 1725 trusted proteins were detected,and the number of differential proteins in each comparison group was different.The expression of peanut protein was significantly affected by temperature,and two types peanut proteins were significant differences in the expression.Based on the results of GO and KEGG analysis,it was found that the related proteins in the process of peanut quality deterioration were involved in stress,defense,energy supply and carbon metabolism,which further affected peanut quality.(4)Lipoxygenase was used to catalyze the oxidation of linoleic acid with different contents,and then an oxidation system was established with peanut protein isolate to simulate the protein oxidation process induced by lipid oxidation in peanut during storage,and the effect of lipid oxidation product-protein interaction on the degree of peanut protein aggregation was investigated.With the increase of linoleic acid concentration,the results showed that the free disulfide bonds content and carbonyl value increased,and the particle size first decreased and then increased,and the surface hydrophobicity changed in the opposite,and the absorption maximum wavelength of the endogenous fluorescence spectrum was first red-shifted and then blue-shifted,and the surface microstructure was destroyed during this process.Complex conformational changes of peanut isolate protein occurred.