Determination Of Fatty Acids In Plant And Cooking Oil By On-line Methylation-Gas Chromatography/mass Spectromerty

The quality of cooking oil is very important for our dietetic life.Resently,illegal cooking oil has become a serious food safety problem in China.It is necessary to develop a fast and accurate analysis method for the discrimination of illegal cooking oil.Furthermore,it is also needed to develop some new oil resources because there is a lack of cooking oil in China.It has been reported that On-line hydrolysis and methylation-gas chromatography/mass spectrometry(OHM-GC/MS)is a simple,rapid and accurate method,suitable for analysis the high-molecular weight samples containing acid and ester components by using organic alkaline regents.In this thesis,a method to determine the composition of fatty acids,in cooking oils,illegal oils and styrax tonkinesis seed oil was developed on the basis of OHM-GC/MS.At First,a method of OHM-GC/MS fingerprint for cooking oil was developed for the discrimination of illegal cooking oil.More than 20 cooking oil samples and illegal cooking oil samples were analyzed by OHM-GC/MS using a vertical microfurance pyrolyzer.The type of the organic alkali and the methylation temperature were optimized.1 ?L(3mg/mL)oil sample and 2 ?L organic alkali,tetramethylammonium hydroxide(TMAH,25%methanol solution)taken in a sample cup was first mounted at the waiting position of the pyrolyzer kept at around room temperature,then it was dropped into the heated center of the pyrolyzer under the flow of helium carrier gas.On-line hydrolysis and methylation of the samples at 350°C in the presence of TMAH,allowed analysis of fatty acids as their corresponding methyl derivatives,and the products formed were introduced into a gas chromatograph equipped with a flame ionization detector or mass spectrometer.Based on the relative peak areas of 10 peaks in the chromatogram obtained by OHM-GC,the samples were clearly classified by principle component analysis and hierarchical cluster analysis.The fingerprints developed showed a high similarity and a good reproducibility,and the pattern recognition techniques can distinguish illegal oils from cooking oils well.The results proved that it is a simple,rapid and accurate method,suitable for the discrimination of illegal oil.Secondly,a method to determine the composition of fatty acids in styrax tonkinesis seed oil,seed pulp and seed shell was developed by OHM-GC/MS using a vertical microfurance pyrolyzer.On-line hydrolysis and methylation of styrax tonkinesis samples at 350? in the presence of trimethysulfonium hydroxide(TMSH),allowed analysis of fatty acids as their corresponding methyl derivatives.The main fatty acid were palmitic acid(C16:0),stearic acid(C18:0),oleic acid(C18:1),linoleic acid(C18:2)and linolenic acid(C18:3).At the optimum conditions,the RSDs of the fatty acids less than 3.81%(n=5).Furthermore,the discrimination of the samples from different growing places and different edible oil species was achieved by similarity matrix on basis of the chemical composition for their fatty acids.The results showed that it is a simple,rapid,accurate method for the determination of the composition of fatty acids in styrax tonkinesis.Lastly,a method to determine the composition of styrax tonkinesis seed shell was developed by OHM-GC/MS using a vertical microfurance pyrolyzer.On-line hydrolysis and methylation of styrax tonkinesis samples at 350? in the presence of trimethysulfonium hydroxide(TMSH),more than 20 components was qualitative and quantitative analyzed.Furthermore,the discrimination of the samples from different growing places was achieved on the basis of their chemical compositions.The obtained results can be used as a reference for the comprehensive utilization of the styrax tonkinesis seed oil.