Avaliação da capacidade antioxidante e perfil químico de extratos da fibra da casca do coco (Cocos nucifera L. Palmae)

Abstract

The present study aims to determine the antioxidant capacity of the ethanolic extracts of husk fiber of four coconut (Cocos nucifera L.) varieties (yellow dwarf, green dwarf, giant and hybrid), aiming to verify their possible utilization as natural antioxidants. For this, their total phenolic content, radical DPPH• scavenging activity, reducing ability towards iron ions (FRAP) and copper ions (CUPRAC) and inhibition of lipid peroxidation using a biomimetic membrane system were analysed. The electrochemical investigation using a glassy carbon and a modified glassy carbon electrode, and the identification of some chemical constituents were performed by cyclic and differential pulse voltammetry and liquid chromatography coupled with UVVIS spectrometry (CLAE-UV/DAD) and mass spectrometry, respectively. The higher value of total phenolic content was found for the hybrid variety: 531 ± 24 mg GAE g-1 dry extract and the lowest was for the green dwarf with 58 ± 9 mg GAE g-1 dry extract. The ability of the extracts to scavenge DPPH• radicals was in the order giant> yellow dwarf > hybrid > green dwarf and IC50 values varied from 8.6 to 55.9 μgmL-1. All varieties showed reducing potential by the use of FRAP and CUPRAC methods, with the lowest performance obtained for the green dwarf variety. Through the use of mimetic biomembranes, ethanolic extracts of coconut husk fibers were shown to protect lipids against oxidative damage independent of the variety. Cyclic voltammetric studies of the ethanolic extracts on glassy carbon electrode confirmed the presence of easily oxidized compounds, and the high antioxidant capacity of the varieties. This was expressed as mg quercetin equivalents g-1 dry extract and ranged from 25.9 – 53.5 mg QE g-1 dry extract using a glassy carbon xanthurenic acid modified electrode (GCE/MWCNT/ poly-Xanthurenic Acid). The investigation of phenols using CLAE-UV/DAD revealed the presence the catechin, quercetin, chlorogenic, vanillic, ferulic, caffeic and gallic acids. Our findings suggest that these extracts can be an important source of natural antioxidants for use in food and possibly in the pharmaceutical and cosmetic industry, aggregating value to the enormous amount of waste from the coconut industry.