Regularity And Factors Of Monoepoxy Fatty Acids Formation During Deep-frying

Monoepoxy fatty acids are oxidized fatty acids produced by double bond epoxidation during oil deterioration.It belongs to total polar component as safety evaluation index of the frying oil,which poses a threat to human health due to high absorption rate and potential toxicity.However,most related researches focused on the total polar component and pay little attention to monoepoxy fatty acids.At present,the distribution of monoepoxy fatty acids in the heating process and its influencing factors have been reported.Composition of oleic acid and linoleic acid are one of the important factors.But the formation of monoepoxy fatty acids in the frying process and influencing factors have hardly been reported.Therefore,this paper focused on the formation of monoepoxy fatty acids in the frying process,as well as the effect of the ratio and total amount of oleic acid and linoleic acid on the formation of monoepoxy fatty acids during frying,to guide the optimization and quality control of frying oil.The main research contents are as follows:Firstly,the gas chromatography-mass spectrometry was applied to detect the monoepoxy fatty acids produced by the deterioration of edible oils.The identified monoepoxy fatty acids included cis/trans-9,10-monoepoxystearic acid(m/z 155,m/z 199),cis/trans-9,10-monoepoxy oleic acid(m/z 155,m/z 185),cis/trans-12,13-monoepoxy oleic acid(m/z 164,m/z 207)by NIST library and characteristic ion fragments.Secondly,the content of monoepoxy fatty acids and the index of deterioration in the frying oils with different ratios of oleic acid to linoleic acid were monitored,and the effects of the ratios of oleic acid to linoleic acid on the above indicators were discussed.The results showed that the total content of monoepoxy fatty acids and monoepoxy stearic acids in the frying oil with a 2:1 ratio of oleic acid and linoleic acid were the highest,reaching 7.20 mg/g and 5.92 mg at 24 h,respectively;The frying oil with a 1:2 ratio of oleic acid and linoleic acid had the highest content of monoepoxy oleic acids,total polar component,oxidized triglyceride polymers,oxidized triglyceride and epoxy value,reaching 1.68 mg/g,30.02%,19.41% and 8.59% and 0.18% respectively.Therefore,the ratio of oleic acid to linoleic acid has different effects on monoepoxy fatty acids and indicators of deterioration.The content of monoepoxy fatty acid and the index of deterioration in the frying oils with different amounts of oleic acid and linoleic acid were also monitored,and the effects of total oleic acid and linoleic acid on the above indicators were further discussed.The results showed that the total monoepoxy fatty acids,monoepoxy stearic acids,monoepoxy oleic acids,total polar component,oxidized triglyceride polymers,oxidized triglyceride and epoxy value were the highest in the frying oil with the highest amounts of oleic acid and linoleic acid,reaching 10.53 mg/g,9.03 mg/g,1.50 mg/g,31.85%,20.51%,9.24% and 0.21%,respectively.Therefore,the total amount of oleic acid and linoleic acid has a consistent effect on monoepoxy fatty acids and indicators of deterioration.Thirdly,the formation regularity of monoepoxy fatty acids in the frying process was summarized by analyzing the correlation between monoepoxy fatty acids and the deterioration of frying oil.The results showed that monoepoxy fatty acids were significantly positively correlated with total polar components,oxidized triglyceride polymers and oxidized triglycerides except for hydrolysis products;The total monoepoxy fatty acids were most correlated with the formation of total polar components and polymers(p<0.01);the formation of monoepoxystearic acids and total polar components were the most relevant(p<0.01);monoepoxyoleic acids were highly correlated with the formation of total polar components,oxidized triglyceride polymers,and oxidized triglyceride(p<0.01).Therefore,the formation of polymers may be accompanied by the formation of a monoepoxy fatty acids.In order to effectively reduce the monoepoxy fatty acids content in the frying oil,in addition to controlling the formation of the total polar component,in particular,the formation of the oxidation products and the polymers should be inhibited.Finally,the practicality of using the epoxy value by titration method to characterize the quality of frying oil was discussed.The results showed that the epoxy value was most correlated with the formation of total polar components(p<0.01),and it was significantly positively correlated with total monoepoxy fatty acids(p<0.01),showing a good linear fit.Therefore,the epoxy value has a potential for rapid assessment of total monoepoxy fatty acids content.