In addition, aluminium chloride forms acid labile complexes with the orthodihydroxyl groups in the A- or B-ring of flavonoids (Chang et al., 2002). From the results, the concentration of flavonoid in the extracts was expressed as mg of catechin equivalents per g of the extract, as shown in Table 1. For total flavonoid content determination, the result showed the same trend with total phenolic content. The total flavonoid in the methanolic extracts was in range of 8.5 mg GAE g to 1.97 mg GAE g Dry Weight (DW). Rhizome of Z. vinosum displayed highest total flavonoid content (p<0.05) while stem of E. velutina is the lowest. Flavonoid compounds in plant have been reported to possess effective antioxidants properties (Cai et al., 2006) and are important phytochemical. Flavonoids are naturally occurring phenolic antioxidants that are present in the human diet. Some flavanoids have been reported to possess a variety of biological functions including antiallergic, antioxidants, anti-inflammatory, antiviral, antiproliferative and anticarcinogenic activities, in addition to having effects on mammalian metabolism (Ren et al., 2003).
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