Analysis Of Oxidation Products Of C18 Unsaturated Fatty Acids In Oils

Vegetable oil is one of the indispensable foods in people's daily life.Due to the difference in the distribution and content of fatty acids in each vegetable oil,the degree of oxidation is different during daily storage and consumption,especially vegetable oil with high unsaturated fatty acid content,which is much easier to oxidize.Unsaturated fatty acids are highly susceptible to oxidative cleavage in the presence of oxygen,forming volatile and non-volatile materials that will alter the functional properties and nutritional value of the oil.How to relieve the automatic oxidation of oil,that is,to effectively improve the stability of oil has become an important problem.Therefore,studying the dynamic changes of C18 unsaturated fatty acid auto-oxidation in oils and fats is of great significance not only in terms of theoretical value but also in economic value.In this paper,the research objects are camellia seed oil with oleic acid as the main fatty acid and linseed oil with linolenic acid as the main fatty acid.The system is investigated in the simulated normal temperature accelerated oxidation(heating at 60? for 1-14 d)and high temperature oxidation(Dynamic changes of oxidation index and oxidation products during oxidation at 100?,120?,140?,160?,180?,200? for 1 h,3 h,5 h).Under these conditions,the peroxide value of camellia seed oil is 2.45?65.73 mmol/kg.The acid value is 0.32?1.52 mg KOH/kg,and the carbonyl value is 4.39?21.19 meq/kg.The peroxide value of linseed oil is 2.65?124.67 mmol/kg.The acid value is 0.56?2.98 mg KOH/kg,and the carbonyl value is 4.83?44.54 meq/kg.The primary product hydroperoxides and the secondary product carbonyl compounds produced by oxidation of camellia seed oil and oxidized linseed oil were detected by liquid chromatography and mass spectrometry.The primary products detected in oxidized camellia seed oil are oleic acid and linoleic acid hydroperoxides,and the content of linoleic acid hydroperoxides are higher than that of oleic acid hydroperoxides.After 14 days of oxidation at room temperature,the contents of nonanal,pentanal,hexanal and trans-2-nonenal in Camellia seed oil were 15.43 mg/kg,2.99 mg/kg,19.03 mg/kg and 5.02 mg/kg,respectively.After heating at 180? for 3 h,the content of carbonyl compounds in Camellia seed oil was the highest,and the contents of nonanal,pentanal,hexanal,trans-2-nonenal and trans,trans-2,4-nonadienal were 20.05 mg/kg,1.42 mg/kg,0.80 mg/kg,0.94 mg/kg,and 1.92 mg/kg,respectively.The primary products detected in oxidized linseed oil are linoleic acid and linolenic acid hydroperoxides,and the content of linolenic acid hydroperoxides are higher than that of linoleic acid hydroperoxides.After 14 days of oxidation at room temperature,the contents of propanal,trans-2-butenal,trans-2-pentenal,trans-2-hexenal,hexanal,trans-2-nonenal,trans,trans-2,4-nonadienal were 4.23 mg/kg,1.35 mg/kg,0.80 mg/kg,1.59 mg/kg,6.97 mg/kg,5.92 mg/kg,1.98 mg/kg and 8.94 mg/kg,respectively.After heating at 180? for 3 h,the content of carbonyl compounds in linseed oil was the highest,and the contents of propanal,trans-2-pentenal,trans-2-hexenal,hexanal,trans-2-nonenal,trans,trans-2,4-nonadienal and nonanal were 16.33 mg/kg,0.66 mg/kg,1.13 mg/kg,1.23 mg/kg,0.47 mg/kg,1.00 mg/kg and 0.89 mg/kg,respectively.In addition,the experiment combines the quantum chemical density functional theory to derive the dynamic process of oxidation of C18 unsaturated fatty acids in oils and fats from the perspective of bond energy and bond angle change.In order to provide some guidance for people to store and consume vegetable oil with high unsaturated fatty acid content,provide theoretical basis and certain technical reference.