Multi Detection Methods for Analysis of Adulterated Sesame Oil (Sesamum indicum L.)

Abstract

This study was performed for the development of identification if added in sesame oil. Methods to identify the other vegetables oil. Sesame oil was extracted from sesame seeds originating from different countries. Adulterated sesame oil were prepared by mixing corn oil in the ratios of 0, 5, 10, 20, 30, 40, 50, 75, 80 and 100% (v/v). Soybean and rapeseed oils were also added in ratios of 0, 5, 10, 20, 40, 80 and 100% (v/v). Detection methods for adulterated sesame oil such as analysis of fatty acid by GC-FID and GC/MS, sesamin content by HPLC analysis, carbon isotope ratio and NIR spectroscopy were investigated. Also, the analysis method of volatile organic compounds by GC/MS in sesame and other vegetable oils was compared. When sesame oil is adulterated with corn oil, adulteration ratio of corn oil more than 5% can be estimated from the ratio of C16:0×C18:2×C18:3/C18:0+C18:1 fatty acids. The linear regression coefficient (r2) for this analysis was 0.987 and a simple equation of y=0.0072x+1.2951 was fit to the data. Soybean oil in adulterated sesame oil can be detected by the content of linoleic acid and the ratio of C18:1/C18:2 fatty acids, and rapeseed oil can be detected by the content of linoleic and erucic acid and the ratio of C18:2/C18:1 fatty acids. Linoleic acid content of more than 0.5% can be used to estimate the percent of foreign corn, soybean and rapeseed oils, and linoleic acid content of more than 1% can be used to estimate the percent of foreign soybean and rapeseed oils. Linoleic acid contents between 0.5% and 1% can be detected by carbon isotope analysis. Analysis of sesamin content by HPLC was not applicable to the detection of adulterated sesame oil because sesame oils of different origin contain various ranges of sesamin. NIR spectroscopy was useful for discriminating the geographical origin of sesame oil but not for detection of adulterated sesame oil. Analysis of volatile organic compounds by GC/MS may be useful as a detection method for adulterated sesame oil because corn, soybean and rapeseed oils have characteristic compounds In conclusion, corn, soybean and rapeseed oil contents of more 10% (v/v) in adulterated sesame oil can be easily detected using the above methods.