Effects of Ethanolic Leaf Extracts of Neem (Azadirachta indica) on Oxidative Stability of Palm Oil

Abstract

Background and Objective: The search for natural alternatives in oil and food preservation is on the increase considering the potential health impact of using synthetic antioxidants. It is in attempt to bridge this gap that this study was designed to test the potency of leaf extract of neem (Azadirachta indica) in reducing peroxidation and stabilizing palm oil during storage. Materials and Methods: The neem leaf extract was carried out by cold maceration using ethanol as the extraction solvent. The ethanolic leaf extract was then evaluated for chem. composition using GCMS and UV-spectroscopy. Antioxidant activity on the extract was determined by 1,1-diphenyl-2-picrylhydrazyl (DPPH); β-carotene linoleic antioxidant activity, oxygen reducing antioxidant capacity (ORAC) and ferric reducing antioxidant power (FRAP) efficacy using standard procedures. Oil samples were prepared and treated with the plant leaf extracts using four different concentrations (100, 200, 400 and 800 mg L-1) on storage for 6 mo. Thereafter, chem. properties of the oil samples including peroxide value, anisidine value, iodine value, acid value, saponification value as well as sensory evaluation was also conducted on monthly basis throughout the storage period. Results: The results revealed the presence of certain bioactive compounds and their functional groups previously shown to facilitate antioxidant activities. Similarly, the extract had significant antioxidant effect for DPPH (12.5400±0.0173 IC50 (%) inhibition); β-carotene linoleic antioxidant activity (43.8233±0.0251 IC50 (%) inhibition), ORAC (4.6500±0.0200 μ Mol TE g-1) and FRAP (286.4267±0.0378 μ Mol Fe2+ L-1). Oil samples treated with the leaf extracts during storage show significant retardation of oxidation compared to untreated samples. In addition, sensory evaluation on a five-point hedonic scale revealed that all samples were generally acceptable. Conclusion: This study has given plausible evidence to support the use of Azadirachta indica as a natural antioxidant to prevent vegetable oils oxidation during prolonged storage.