Cocos nucifera (coconut) husk fiber is the dry and fibrous external material that is processed typically to obtain the solid albumen and endosperm (coconut-water). It has been reported previously that the husks of the coconut palm are discarded massively as waste and considered as a major agro-waste of tropical countries. In this study, we investigated and compared the antioxidant activities of the n-hexane and acetone-water extracts of varieties of Cocos nucifera husk fibre - wild mature (WM), dwarf (DWF), young (YNG), and hybrid (HYB). The antioxidant activities of extracts were evaluated using a range of in vitro free radical scavenging assay models, total antioxidant capacity, and reductive ability. The results obtained were statistically analysed at a significance level of p < 0.05. The highest values for the total flavonoid content, total phenolic content, and total antioxidant capacity for the n-hexane extract was obtained from the wild mature husk fibres while the lowest was from dwarf species. The acetone-water extracts of the young husk exhibited the highest values for the total flavonoid, phenolic content, and antioxidant capacity while the hybrid species showed the lowest. At varying concentrations, the coconut varieties and extracts displayed different 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals scavenging activities. All varieties displayed reducing potential, although with varying efficacy. Also, it was observed that the IC50 for the nitric oxide free radical scavenging activity of the n-hexane extracts and acetone-water extract were similar in the order of HYB > DWF > WM > YNG.
