The Research Of Fatty Acid Composition Of Vegetable Oils Affected By Frying Condition And Correlated To The Quality

This study intends to do some experimental analysis of deep fried oil in the kitchen toexplore the changes of fatty acid composition with the changes of frying temperature andtime in rapeseed oil, peanut oil, corn oil, sunflower oil, and tea seed oil; The relevancebetween fat acids and the quality of oil(K232,the value of UV characteristic absorption peakat232nm wavelength)was respectively analyzed, this study carried out the following tasks:1. methyl esterification method selectionThis test compared the effect of six different methyl esters methods to methyl esterderivative of the fatty acids in five different vegetable oils by examining the methylatedsamples through gas chromatography-mass spectrometry (GC-MS). Base-catalyzedmethod was selected to be the best method: weighed about100mg oil into10mL plug testtube, added n-hexane, diethyl ether and1mol/L KOH/CH3OH solution each1mL,standing30min after ultrasonicing10min, added ultrapure water until the surface ofsolution near the mouth of the tube, stand30min after fully shock, added1mL of then-hexane again, got liquid supernatant, and dried by Na2SO4analyzed by GC-MS. Theresults showed: The Base-catalyzed method the majority of fat acids can be esterified, atthe same time, the degree of esterified substitution completely, with simple operation, andshort time-consuming.2. GC measurement conditions selectionIn order to improve the separation of fatty acid methyl ester, a comprehensivecomparison of two kinds of temperature-programmed conditions to find out the betterseparation was did. Finally there better condition was: The initial temperature was kept3min at140℃, raised to180℃at the rate of3℃/min and kept1min, and then raised to220℃at the rate of1℃/min and kept7min. The chromatogram chart showed that therewere no tailing peaks, the peak shape was symmetric, and most of the fatty acid peakscould be tested.3. The law of the changes of the fat acid composition effected by fryingtemperature and timeRespectively using five vegetable oil to fry potato chips at at150℃,180℃, and210℃, the oil samples were taken at4,8,12,16,20,24,28,32h during frying. GC-MS was usedto detect the composition of fatty acid. The results showed that the higher fryingtemperature or longer frying time can result the increasing of the content ofMedium-carbon-chain fatty acid（MCFA）、Odd-carbon-chain fatty acids（OCFA）、Trans fatty acid（sTFA）、Saturated fatty acid（sSFA）, while the values of Long-carbon-chain fattyacids (LCFA)、Polyunsaturated fatty acid（sPUFA）、the relative degree of unsaturation(U/S)were decreased when the frying temperature was higher or the frying time was longer.4. The correlation between the content of fat acid and K232Detecting the values of K232sampled by the method above. Using SPSS software torespectively analyze the correlation of MCFA、OCFA、TFA、LCFA、SFA、Monounsaturatedfatty acids（MUFA）、PUFA、U/S and K232.The results showed that these8values aresignificantly correlated (p <0.01) to K232,while the coefficients of determination aredifferent; in five vegetable oils,7values showed a linear correlation to K232expect MUFA,which showed a polynomial correlation. And the coefficients of determination betweenSFA、MUFA、U/S and K232were large in every oil, so SFA, MUFA, U/S can be used toevaluate the quality of these five kinds of vegetable oils.