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Summary A simple spectroscopic method using 2,2-diphenyl-1-picrylhydrazyl (DPPH) was developed to simultaneously monitor the contents of free radical scavenging antioxidants (FRSs) and oxidised lipid products during oxidation through selection of proper solvents. Validation of the DPPH method was conducted in a stripped oil matrix, and practical applicability of the method was tested with heated oils. The absorbance of DPPH in isooctane simultaneously reflected the changing amounts of both FRSs and oxidised lipid products, whereas the absorbance in methanol mainly reflected changes in FRSs. Total polar materials (TPMs) were found to be representative of oxidised lipid products, which reacted with DPPH in isooctane better than in methanol. Validation parameters including accuracy, precision, linearity, limit of detection and limit of quantification were determined using α-tocopherol as a model for FRSs and TPMs for oxidised lipid products. The DPPH protocol in isooctane and in methanol is useful for assessing the degree of oxidation in heated oils through comparing the contents of FRSs and oxidised lipids.

Differentiating blended sesame oils from authentic sesame oil (SO) is a critical step in protecting consumer rights. Stable carbon isotope ratios (δ13C), color, fluorescence intensity, and fatty acid profiles were analyzed in SO prepared from sesame seeds with different roasting conditions and in corn oil blended with SO. Sesame seeds were roasted at 175, 200, 225, or 250 °C for 15 or 30 min at each temperature. SO was mixed with corn oil at varying ratios. Roasting conditions ranging from175 to 250 °C at the 30 min time point did not result in significant changes in δ13C (P > 0.05). Values of δ13C in corn oil and SO from sesame seeds roasted at 250 °C for 15 min were −17.55 and −32.13 ‰, respectively. Fatty acid ratios, including (O + L)/(P × Ln) and (L × L)/O, where O, L, P, and Ln were oleic, linoleic, palmitic, and linolenic acids, respectively, showed good discriminating abilities among the SO blended with corn oil. Therefore, using different combinations of stable carbon isotope ratios and some fatty acid ratios can allow successful differentiation of authentic SO from SO blended with corn oil. Practical Application: Adulteration of sesame oil with less expensive oils such as corn oil or soybean oil to reduce cost is a common unethical practice in Korea. Due to the unique and strong flavor of sesame oils that may mask other weaker flavors, however, differentiating authentic sesame oils from blended oils is difficult. This study showed that the roasting process did not significantly affect the ratios of the stable carbon isotope (δ13C) in sesame oils. δ13C was confirmed to be a reliable parameter. Moreover, some fatty acid ratios were designed to discriminate between blended sesame oil with corn oil and authentic sesame oil.