Antioxidant properties of orange and lemon peels and their efficacy in preventing lipid peroxidation in stored oils

The role of natural antioxidant compounds in preserving the frying stability of oils is increasingly recognized. Orange (Citrus x sinensis) and lemon peels (Citrus × aurantiifolia) are rich sources of antioxidant components. The objective of the current study was to determine antioxidant properties of orange and lemon peels and evaluate their efficacy in preventing lipid peroxidation in heated and stored unrefined sunflower (Helianthus annuus) and groundnut oils (Arachis hypogaea). Peel powder was added at 0.5 and 1.0% level. The oils were subjected to thermal treatment, stored and analyzed on 0, 10, 20, and 30 days for the determination of free fatty acid (FFA) and peroxide value (PV). The obtained results showed that orange peel had higher total polyphenolic, tannins, β-carotene and total carotene contents. The highest DPPH radical scavenging activity was observed in pure methanolic extract (70%). FFA ranged from 0.03-0.1 and 0.04-0.1% in sunflower oil heated at 60 ºC with 0.5 and 1.0 g peel powder, respectively. FFA was in the range of 0.35-0.45% for groundnut oil samples heated at 60 ºC with 0.5 g peel powder, whereas PV ranged between 3.65 and 8.4 meq/kg. The reduction in lipid peroxidation during storage of heat treated peel powder incorporated samples was remarkable for those heated at 60 °C and stored for 10 days. Lemon peels were also rich in total phenols (716 mg/100 g) and flavonoids (168 mg/100 g) and showed considerable antioxidant activity. At the end of the storage duration, both thermally treated groundnut and sunflower oils showed lesser FFA over the ranges 0.12-0.15% and 0.38-0.52%, respectively and PV ranging from 8.96 to 11.5 meq/kg and from 7.9 to 10.9 meq/kg, respectively than control oils (FFA-0.18-0.9% and PV-12.2-21.2 meq/kg). This study showed that orange and lemon peels may be used as natural antioxidant agents to prevent lipid peroxidation.