The Thermal Oxidative Deterioration Of Edible Oil Composition And Content Changes Of Its Trans Fatty Acid During Deep Frying Process

With the improving quality of life,the public concern more about the food safety.As one of the harmful substances presenting in the food,trans fatty acid(TFA)attracted extensive attention.Based on the current study,the TFA in food are maily produced from hydrogenation of vegetable oil and thermal process(for example,grilling and frying etc.).On the basis of previous studies,this paper created different models,such as edible oil types,thermal processing temperature,thermal processing time,continuous-intermittent use of frying oil and antioxidants,to explore the relationship between these factors and formation of TFA in the edible oil and fried foods.The main results are presented as follows:(1)A new method for the determination of the fatty acid methyl esters(FAME)with gas chromatography and flame ionization detector was established.The precision(RSD)of this method is from 0.38 to 5.67%,and the stability of the derived samples within 12 h was 1.82 to 2.62%.The LOD and LOQ was 0.42?2.50?g/mL and 1.39?9.09 ?g/mL,respectively.the recoveries was in the range of 89.84 to 115.72%,indicating good separation of the detect methods.It has high sensitivity,good accuracy and can be used for the detection of fatty acids in the oil.(2)Fatty acid composition of soybean oil,palm oil and camellia oil,was determined and compared.The main fatty acid in them was cis-linoleic acid(53.11%),palmitic acid(50.04%),cis-oleic acid(82.26%),respectively.With a common used temprature,the TFA in soybean oil and palm oil didn't change with the time.However,The TFA in camellia oil was increased,and trans linolenic was generated.The acid value(AV)increased significantly in the order as camellia oil>palm oil>soybean oil.The peroxide value(POV)of soybean oil first increased and then decreased.Both AV and POV didn't exceed the health standards of China.With the frying temperature of 170 ?,these three kinds of vegetable oil could be recyclely used within 8 h.The FA composition of fryied chicken fillets was similar with the frying oil,which indicated that the trans level in frying materials and the frying oils can affect each other due to fast exchange of fats during frying.With the extention of frying time,total TFA content in chicken fillets increases in the order as soybean oil>camellia oil>palm oil.(3)The relationship among temperature,processing way,frying time and oxidation deterioration of the palm oil was studied.Small changes were observed in the formation of TFA at lower frying temperatures(?200 ?).However,with extrame condition(?250?)TFA formation in the oil significantly increased..No significant difference in the component and content of FA was found between Continuous and intermittent use of frying oil on.The results of AV and POV test also showed that the two processing way had no difference in fat oxidation.The FA in chicken fillet and frying oil exchange from high concentration to low concentration.When temperature ? 200 ?,the TFA content in the chicken fillet had no significant change,while ? 250 ?,trans C18:2,trans C18:3 and trans C18:1 were incresed greatly.(4)Suppressing effects of three natural antioxidants(carnosic acid,polyphenols,natural VE)on the TFA formatin of soybean oil and its and oxidation was studied.The anti-isomer effects of them was in the order as polyphenols>natural vitamin E>carnosic acid.And they showed different inhibitory effects for trans fatty acids with different number of double bonds,the most obvious effect was found for trans-oleic acid,followed by trans-linolenic acid and trans-linoleic acid.According to the POV,with the heating time from 0 to 4 h,soybean oil with addition of natural VE was best in antioxidant activity and carnosic acid was always the worst.Within 4 to 24 h,the antioxidant effect of natural vitamin E was the same with that of tea polyphenols.According to the anisidine value,the antioxidant effect ordered as tea polyphenols>natural VE>camosic acid.According to the values of malondialdehyde(MDA),the antioxidant effect ordered as tea polyphenols>natural VE>carnosic acid.As phenolic antioxidants inhibit lipid peroxidation chain reaction by the release of hydrogen ions,the different antioxidant effect of them may be due to its different ability to release hydrogen ions.