Ultrasound-assisted deep eutectic solvent (DES) extraction of coconut dregs as a natural antioxidant to improve the chemical quality and stability of coconut oil

Abstract

Coconut dregs (CD), a by-product produced from the coconut milk industry, are high in antioxidant compounds and have the potential to act as a natural antioxidant. It can be considered as an alternative to synthetic antioxidants in the food industry. This research aimed to determine the total phenolic and total flavonoid content of coconut dregs extract using deep eutectic solvents (DES) as a green extraction method and to analyse the stability of coconut oil incorporated with different concentrations of coconut dregs extract during storage. The antioxidant properties of the CD extract were studied for total phenolic content (TPC), total flavonoid content (TFC), and 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging capacity. The CD extract exhibited a TPC of 44.259 ± 0.059 mg GAE/g (p < 0.05), a TFC of 24.211 ± 0.469 mg QE/g (p < 0.05), and a DPPH scavenging activity of 77.15 ± 1.58% (p < 0.05). The oxidative stability of coconut oil was assessed through peroxide value (PV), p-anisidine value (AV), and thiobarbituric acid reactive substances (TBARS). In this study, the results showed that untreated coconut oil exhibited the highest PV (6.75 meqO2/kg), AV (4.18), and TBARS (1.54 MDA eq/kg) at day 15, indicating advanced oxidation. In contrast, oils treated with CD extracted at 5% and 10% concentrations recorded significantly lower values, with 10% CD extract achieving PV, AV, and TBARS levels of 3.75, 2.62, and 0.83, respectively (p < 0.05). These results indicate that the CD extract was comparable to the synthetic antioxidant BHT, highlighting its efficacy in reducing oxidative degradation.