The Study On Quality Change And Oxidation Stability Of Canola Oil During Frying Process

This paper proceed several experiments of frying fries,in which EE Canola oil extracted by physical pressing and SE Canola oil extracted by chemical extraction were used as frying medium.Then,the changes of physicochemical properties,nutritional components and oxidation stability of Canola frying oil during different frying time were studied.The scientific basis on full use of the nutritional value of Canola oil could be provided in this paper.The main research results are as follows.After 6 days of continuous frying,the smells of Canola oil were aggravated;and the foam increased.Moreover,the oil fume was gradually produced and the color and luster of oil were deepened.The acid value,peroxide value,p-anisidine value and K value of Canola oils increased as the prolonging of frying time.However,the above indexes in unfried EE oil and SE oil were no significant difference.And the change rate of each index of SE oil was faster than EE oil at the same frying time.In the frying process,the contents of total polar compounds,diacylglycerols,oxidized triglycerides and free fatty acids also gradually increased with the increasing frying time.The volatile components of Canola oils during frying process were determined by solid-phase microextraction and gas chromatography-mass spectrometry.The results showed that the unfried Canola oil has less volatiles content,mainly including alkane and esters.And the variety of volatile components in Canola oil increased with the prolonging of the frying time.And the contents of nonanal,hexanal,2-Decenal and 2,4-Heptadienal were increased,significantly.After 6 days of consecutive frying experiment,the changes of nutrients in EE and SE oil were investigated.The total phenolic content in EE and SE oil decreased by 39%and 71.8%after 6 days frying,and the loss ratio of the sterols content was 15.53%,9.82%,respectively.The losses of tocopherols were the most serious,particularly in SE oil.The results showed that the losses of tocopherol monomers in Canola oil from large to small were:?+ ?-tocopherol>?-tocopherol>?-tocopherol.After frying process,the contents of monounsaturated fatty acids and saturated fatty acids of Canola oils increased relatively,while polyunsaturated fatty acids showed the opposite trend.The antioxidant tests in vitro were carried out,through DPPH,ABTS and FRAP.The results showed that the antioxidant capacity of Canola oil showed a significant decrease with the prolonging of frying time.Through the analysis of the polarity component,oxidative induction time and bioactive substance of EE oil and SE oil,it was found that the content of polar substance in EE oil was lower than that in SE oil.And the induction time of EE oil was longer than that in SE oil with the same temperature.These results showed that the thermal oxidation stability of EE oil was stronger than SE oil.The contents of polyphenols,tocopherols,sterols,phospholipids,saturated fatty acids and monounsaturated fatty acids in unfried EE oil were higher than that in SE oil,however,the contents of polyunsaturated fatty acids were higher in SE oil.Therefore,Canola oil with the high contents of bioactive substance would have the better oxidation stability.