The Changes Of Glyceryl Ester Core Aldehydes And Their Influencing Factors During Deep-frying

Glyceryl ester core aldehydes(GCAs)are one of typically non-volatile aldehydes with higher molecular,characterizing by aldehydic acids bonded to glycerol skeleton with acyl group.They are common present in deep-frying and heating oils,which are considered potentially hazard to consumers.However,the reports on their natures in actual frying systems have not been seen at home and abroad.To this end,this study systematically studied on the profile,level and variety of GCAs in different thermal processing and deep-frying oils,investigated the correlation between GCAs and indicators of deterioration and analyzed their major influencing factors.The main contents are as follows:Firstly,the GCAs in one actual deep-frying oil were identified by gas chromatographymass spectrometry,which were characterized by NIST library matching and characteristic ion fragment analysis,and then quantified by internal standard substance.The results showed that there were three methyl esterification products of GCAs such as methyl 8-oxooctanoate(Me-8-oxo),methyl 9-oxodecanoate(Me-9-oxo)and methyl 10-oxo-8-decenoate(Me-10-oxo-8),which were corresponded to GCAs(8-oxo),GCAs(9-oxo)and GCAs(10-oxo-8)respectively.The content of GCAs in the frying oil was at the level of mg/g.Secondly,the GCAs in thermal processing were systematically studied,in which high oleic sunflower oil(HOSO),soybean oil(SBO)and flaxseed oil(FO)were heating at different temperatures for 12 h.The influence of heating time,temperature and fatty acid composition on the profile and level of GCAs were analyzed.The results showed that the content of GCAs in different heating systems increased linearly with the heating time(within 12 h),and the heating process increased the content of GCAs in the oils significantly(p<0.05).After heating for 12 h,the average content of GCAs in the heating system of different oils was significantly different(p<0.05),which was sort as HOSO>SBO>FO.When the same oil was heated at different temperature,the average content of GCAs was sort as 120°C>180°C>140°C>160°C.It showed that the oil rich in monounsaturated fatty acid produce more GCAs during thermal processing,and the GCAs in heating systems were the least when the heating temperature was set as about 160°C.Thirdly,the Pearson correlation and one-dimensional linear regression analysis were performed on the degradation indicators and GCAs in the heating system.The results showed that the content of GCAs was significantly correlated with acid value,peroxide value,total polar component,oxidized triglyceride polymer and oxidized triglyceride monomer(r>0.6,p<0.01).And there was a strong positive correlation(r>0.9,p<0.01)between monounsaturated fatty acids and GCAs,but a strong negative correlation with polyunsaturated fatty acids(r<-0.9,p<0.01).The linear regression analysis showed that the changes of GCAs in thermal processing oils were intrinsically linked to the oxidation,decomposition and polymerization of oil.The content of GCAs was expected to be used to indicate the deterioration of oils.Finally,the variation of GCAs and their influencing factors in the actual deep-frying process were studied.The GCAs in nine kinds of actual frying systems were systematically monitored during continuous frying for 60 h,in which chicken nuggets,fish steaks and French fries were fried in rapeseed oil(RO),high oleic sunflower oil(HOSO)and cottonseed oil(CO)respectively.The results showed that the average amount of GCAs in the actual frying systems was about 1.45 mg/g.Among the three types of GCAs detected,GCAs(9-oxo)were the most abundant,accounting for 60% of the total.In the actual frying process,the content of GCAs increased firstly and then remained stable with the extension of frying time.When different foods were fried in the same oil for 60 h,the total amount of GCAs in each system was sort as fish steaks>chicken nuggets>French fries(p<0.05).When the same food was fried in different oils for 60 h,the total amount of GCAs in each system was sort as HOSO?RO>CO(p<0.05).The main influencing factors affecting the variation of GCAs during deep-frying could be moisture content of the foods,frying temperature and oleic acid content of the oils.This study found that three types GCAs were generated in oils during thermal processing and deep-frying,among which GCAs(9-oxo)accounted for 60%.Frying oils rich in polyunsaturated fatty acids produced the least GCAs when the less watery ingredient was fried at around 160°C.