Determination of minor components and oxidative indices of small-scale pressed sunflower oil during storage

Abstract

Oxidation is the main chemical reaction responsible for the deterioration of oil quality. However, the information available on the subject matter does not indicate the extent to which sunflower oil from poor quality-controlled small-scale processing plants deteriorates under different storage conditions. This study aimed to determine the contents of natural antioxidants and trace metals in crude sunflower oil and monitor the biweekly oxidation indices of samples stored in light and dark for three months. The average α-tocopherol concentration, 170.62 mg/kg, was lower than the recommended concentration (403–935 mg/kg), whereas those of β-carotene and total phenols were nutritionally appreciable. The concentrations of the trace metals; Fe (1.78 mg/kg) and Cu (0.13 mg/kg) were within the Codex and UNBS limits. After three months, acid values of oil samples stored under both conditions showed insignificant differences and compared well with the Codex and UNBS standards. The initial peroxide value (5.3 meq O₂/kg) increased dramatically with samples stored under light exhibiting a significantly greater content (66.7 meq O₂/kg) than those stored in the dark (44.4 meq O₂/kg). The peroxide values under both storage conditions at two weeks met the UNBS (10 meq O₂/kg) and Codex (15 meq O₂/kg) standards, and the average value (13.76 meq O₂/kg) in the dark was acceptable for the Codex standard until week four. On the basis of these results, it is advisable that consumption of crude sunflower oil from small-scale processing plants be limited to within one-month post-processing unless processors adopt practical measures to improve the shelf-life of oil.