Efficacy of Different Sesame Oil Refining Stages in Reduction of Heavy Metals, Antioxidant Activity, and Oxidative Parameters

Abstract

The efficacy of different refining stages on physicochemical parameters, heavy metal, and mineral contents of sesame oil were investigated. The sesame oil from different refining stages (crude oil, neutralization, bleaching, deodorization, and refining stages) was taken from the local oil factory in Yazd, Iran. The fatty acid composition of oil samples was determined by GC-FID. The oxidation indexes including peroxide value, p-Anisidine, free fatty acid, TOTOX, total polar material, as well as antioxidant activity (FRAP and DPPH), and total phenolic content were measured. The mineral and heavy metal content of oil samples were analyzed by ICP-OES. Linoleic acid (41.1-42.4%), oleic acid (41-41.4%), palmitic acid (8.3-9.1%), and stearic acid (6.1-6.3%) were reported as the most dominant fatty acids in all oil samples. The results illustrated that the refining process had no significant effects on fatty acid composition except for slight changes in palmitic acid. It was shown that all oxidation indexes, antioxidant activity, total phenolic content and mineral, and heavy metals were decreased during oil refining. The highest decrease in oxidative indexes was reported in the deodorization stage. The total phenolic content, DPPH, and FRAP ranged from 4.79 to 56.56 mg GAE/100 g, 6852.64 to 867.89 mg/ml, and 54.74 to 127.4 mM FeSO4.7H2O in RSO and CSO, respectively, which the highest decrease was shown during the neutralizing stage. The order of metals in RSO was shown as P>Ca>K>Fe>Mg>Al>Cr>Pb>Ni>Cd>Cu>Co. Although all metals were decreased by the refining process, the Pb concentration (0.16 mg/kg) of RSO was evaluated as higher than the permissible limit. Considering that the refining process effectively reduces undesirable compounds, the consumption of crude sesame oil is not recommended.