Characterization of the phenolic constituents in Mauritian endemic plants as determinants of their antioxidant activities in vitro

SummaryThe phenolic constituents of Mauritian endemic plants from the Rubiaceae and Myrtaceae family were assessed and correlated with their potential antioxidant activities in vitro. The antioxidant activities of the plant extracts ranged from 0.27 to 1.49 mmol Trolox equivalent/g FW and from 0.20 to 1.39 mmol Fe(II) equivalent/g FW in the TEAC and FAP assays, respectively, with Syzygium commersonii showing the highest activity in these two systems. Eugenia orbiculata and all the Syzygium species were effective scavengers of hypochlorous acid while Monimiastrum acutisepalum was the most potent inhibitor of deoxyribose degradation. The plant extracts inhibited microsomal lipid peroxidation with low IC50 s ranging from 0.02 to 1.75 mg FW/mL when reaction was initiated with Fe3+/ascorbate and from 0.093 to 1.55 mg FW/mL in the AAPH-dependent lipid peroxidation. The potential prooxidant nature of the plant extracts was compared with ascorbate (250 μM) using copper–phenanthroline assay. The plant extracts at concentrations up to 5 g FW/L were not prooxidant. However, Myonima nitens, Syzygium commersonii, Syzygium glomeratum and Syzygium mauritianum at concentrations of 10 g FW/L had potency approaching 50% of the prooxidant activity of ascorbic acid in vitro, suggesting relative safeties. The total phenolics influenced the antioxidant activities in the TEAC, FRAP and HOCl scavenging assays whereas a negative correlation was observed with the deoxyribose assay. The high levels of polyphenolic compounds and the significant antioxidant activities of these Rubiaceae and Myrtaceae plant family make them suitable candidates as prophylactic agent.