Study On The Method Of Edible Oil By ACF-SPME-GC/TOF

In this paper,active carbon fiber-solid phase microextraction(ACFSPME)and gas chromatography / time-of-flight mass spectrometry(GC/TOFMS)were used to detect the vegetable oil,animal oil and waste cooking oil.1)Through the experiment of the extraction conditions,the optimum extraction conditions were determined: 120? for oil bath,oil sampling 0.1000 g,Na2SO4 0.0100 g,extraction time 50 min.According to the optimized conditions,70-80 species were detected in the peanut oil,soybean oil,sunflower seed oil,olive oil,sesame oil.The volatile compositions of different oil were fatty acids,aldehydes,ketones,lipids and other organic compounds.There were six kinds of volatile fatty acid detected in all oils: valeric acid,caproic acid,octanoic acid,nonanoic acid,palmitic acid,stearic acid.2)The experiment of different extraction times of the same oil sample by the fixed oil amount shows that the extraction times will not affect the stability of the results.The extraction times should be controlled under 4 times.3)The experiment of different activated carbon fibers were found that activated carbon fibers have different adsorption,but the relative content of the fatty acids remained unchanged.Compared with the commercial activated carbon fibers,it was found that the homemade fibers were more sensitive to the extraction of fatty acids and the adsorption capacity was more.4)Different edible oil of several brands in the market was detected and the relative content of volatile fatty acids was not affected by the brand.5)By detecting waste cooking oil of different sources and animal oil of different kinds,the results show that waste cooking oil contains 70-80 species,which is similar to that of vegetable oil.By comparing the contents of volatile fatty acids in the waste oil and edible oil,the new A value method was determined.The A value = the peak area of palmitic acid / peak area of caproic acid: the A value of drainage oil was more than 0.8 and the A value of vegetable oil was less than 0.8.The A value 0.8 as the boundary can be a good area to separate the waste cooking oil and vegetable oil.6)Through the experiment of cooking vegetable oil,the results shows that the content of palmitic acid in edible oil will increase with increasing cooking numbers of edible oil,there is an increasing trend of A value.This experiment proved that A value can reflect the oxidation degree of edible oil.It can be used to distinguish the fried oil and vegetable oil.Then SPSS software was used to analyze different oil to prove the sensitivity of A value.The result shows that A value is sensitive to distinguish edible oil and waste cooking oil.7)By the experiment of mixing waste cooking oil with vegetable oil,the doped curve of A value is deduced,which accords with the regularity of the measured value.The curve is a linear curve,which can be used to detect the proportion of the doped products.It provides a powerful support for the detection of waste cooking oil.According to the doped curve and the cooking regularity,the cooking-doped curves are constructed.Through detecting the A value of 5 times heating of the unknown oil,we will know the oil is used oil or doped oil.If the A value is still located in the cooking curve,the oxidation degree of the product is consistent with edible oil.If the A value is not in the cooking curve,it may be the mixture of waste cooking oil and vegetable oil.8)By the experiment of mixing different edible oil,the A value of the original vegetable oil and blend oil both remained unchanged and the A value is not effective in the error range.It shows that the blend oil can't be detected by the method of A value.9)The detection experiment of pepper oil shows the existence of hydrocarbon substances and most of the materials were saturated hydrocarbons such as tridecane.While in the edible oil,hydrocarbons can't be found in the basic materials except alkenes and alkynes.The result can be used to detect the waste cooking oil as an auxiliary test.It will provide support for the method of A value.Through the above experiments,this paper preliminarily determined the new method of using volatile fatty acids in the identification of waste cooking oil and A value calculation formula is determined.This paper provided a new way for the detection of the waste cooking oil.