Determination And Application Of Conventional Indicators In Oil Samples

In this thesis,the edible oil and gutter oil were used as research objects to detect and compare their conventional parameters such as physical and chemical indexes,metal elements,fatty acids and oil degrading bacteria.The possible detective index of gutter oil was found by analyzing the difference of conventional parameters between edible oil and gutter oil.The main research contents are as follows:(1)The acid value,iodine value,carbonyl value,saponification value,peroxide value and density of edible oil and gutter oil were determined by the national standard method.The results indicated that the acid value,carbonyl value and peroxide value of edible oil were significantly different from gutter oil.Therefore,the three parameters could be utilized as the primary indicators to identify the gutter oil.(2)A new digestion procedure of microwave digestion method was established in this paper.In addition,microwave digestion-flame atomic absorption spectrometry and microwave digestion-graphite furnace atomic absorption spectrometry were established to detect the metal elements of oil samples.The distributions and contents of Ca,Mg,Fe,Cu,Zn,Mn,Cr,Cd and Pb in oil samples were examined by the proposed method.The test performances indicated that the edible oil samples were rich in the nutrient metal elements and were almost free of toxic metal elements such as Cd and Pb.Besides the nutrient elements,Cr,Cd,Pb were also detected in gutter oil samples,and the content of Pb was far beyond the national standard limit value.Based on the results,Cr,Cd and Pb could be used as the preliminary screening indexes of gutter oil.(3)The fatty acids in various oil samples were detected by using gas chromatography in this paper.The results indicated that there were obvious differences in fatty acid components between edible oil and gutter oil.The ratio of unsaturated fatty acids to saturated fatty acids(U/S)was also significantly different in two oil samples.The unsaturated fatty acids had a large proportion in edible oils,and the U/S range was 4.13～10.50.However,the saturated fatty acids such as palmitic acid,stearic acid and lignoceric acid increased significantly,while the unsaturated fatty acid components such as oleic acid,linolenic acid and linoleic acid decreased significantly in gutter oil.The U/S range of gutter oil was only 0.62～0.99.In addition,small molecule fatty acids such as C6:0,C8:0 and C13:0 were also detected in the gutter oil.Therefore,some small molecule fatty acids or U/S could be used to distinguish edible oil from gutter oil.(4)A biological method had been innovatively investigated to identify the gutter oil.The edible oil was used as a matched group,and the oil-degrading bacterium was cultivated and screened in two lipid carbon sources.Finally,two strains of degrading bacteria were screened in the medium with the gutter oil as the sole carbon source.The strains were identified as Enterobacter cloacae and Geotrichum candidum by gene sequence comparison analysis.The growth environment of two oil-degrading bacteria was obviously different because of the sole carbon source.Therefore,the two strains could be used as specific degradable bacteria to distinguish gutter oil from edible oil.