Study On Variation Of Harmful Substances Generated In The Process Of Heating Vegetable Oils

Vegetable oils as the mainly cooking oils of people’s daily life,when heated to high temperatures,frying oils and other conditions can cause a series of chemical changes,resulting in vegetable oil acid value,peroxide value and other indicators of change,and produce toxic substances.In this study,y heating the rapeseed oil,palm oil,corn oil,olive oil,rice oil,soybean oil to 180 ℃,220 ℃,260 ℃ and take samples at each times during each heating temperature,respectively,analyze the changes in the physical and chemical indicators of the heating process,the cis-trans fatty acids changes produce changes,benzo(a)pyrene generation and,changes in four aspects of plant sterols oxide heating process for vegetable fats and oils affect the quality of toxic and hazardous substances,The works of this study are: 1,Toxic and hazardous substances are reviewed--TFAs in vegetable oils during heating process that may arise,B[a]P,the development research of POPs hazards and stage,discusses its causes and detection technology.2,The standardization method was used to detect the acid value,as physical and chemical indicators reflect the changes of the quality of vegetable oil.The reasults show that,under the condition of heating plant oil fatty acid oxidation,then polymerized and produce acids.The higher the temperature and the heating time goes,vegetable oil acid valueincreased more obviously.In the first 2h,the AV is unstable.When heating to 6h,acid accelerated rate of rise in common,this may be due to the intense oxidation of lipid,in the complex,the AV is stable,may be due to the small moleculeacid volatile oil and acid balance.3,By using the method of gas chromatography analysis of the fatty acid in vegetable oil by heating,using sp2560(100m*250m*0.2m)chromatographic column detection,fatty acid elution order for trans fatty acids in the cis isomers before peak.Linoleic acids tended to decrease with the heating time increases with the increase of temperature,the content of oleic acids increased gradually,the content of palmitic acids also showed an upward trend,trans fatty acids are related in the heating process and the change of content and species of plant oils,heating time,heating temperature,the higher the degree of unsaturation are easy to generate TFAs,TFAs species and quantity and vegetable oil in the unsaturated fatty acids are closely related,some vegetable oils in the cis fatty acid content is high,and the corresponding to the trans fatty acid content is higher.4,By using the method of high performance liquid chromatography for heating oil in the Benzo[a]pyrene contents was determined by HPLC,using HiSep C18-T column,Benzo[a]pyrene content is linear in the range of peak area was 0.5 g/L ~ 40 g/L,the standard curvewas y = 0.742 x + 0.733,the correlation coefficient was 0.9997,detection limit for 0.05 μg,the precision of the method well.The B[a]P content in rice oil is the highest,but not exceeding the national standard limit,and Soybean oil,Palm oil,Rapeseed Oil is in different heating conditions did not exceed the standard of B[a]P.The results show that,under the condition of continuous heating B[a]P is first decreased,second increased and then decreased,while thermal in 2h still shows the trend of first decreased and then increased in the second day after.Continuous heating,the change of B[a]P at the start of the 2h gradually increased,mainly because the production and the volatilization of B[a]P reaches a certain balance.Vegetable oils smoke point are different,resulting in different B[a]P volatilization,due to the difference in the vegetable oil fatty acid composition,the rate of B[a]P production are different,the higher degree of unsaturation of vegetable oil to produce B[a]P sooner and more.5,Using GC-MS for heating oil sterol oxides detectation,the conditions of stigmasterol oxidations can be separation and detection well,the experimental results show that the corn oil will produce sterol oxide at 180 degrees and above heating temperature,but in the temperature,POPs are of formation and decomposition,there may be undera few heating time that POPs cannot be detected.Several kinds of plant oil quality decreased obviously in low temperature and short time heating,the generation of hazardous substances is low,but in the long time under the conditions of high temperature and heating oil fatty acid oxidation accelerated itself,pyrolysis intensifies,harmful substances rapidly generated,so the plant oil should avoid high temperature and long time heating.Soybean oil and palm oil in the whole heating conditions of high temperature and long time stable,harmful substances than other types of oil is slightly less,but should avoid the use of high-temperature cooking oil and rice oil.