Proximate composition, mineral content and in vitro antioxidant activity of leaf and stem of Costus afer (Ginger lily)

AIM This study was designed to determine the proximate composition and mineral content of Costus afer leaf and stem, as well as to identify the most active antioxidant fraction. MATERIALS AND METHODS The proximate composition and mineral analysis of C. afer leaf and stem were performed using the standard methods described by Pearson and Association of Official Analytical Chemist while the 1,1 diphenyl 2 picryl hydrazyl (DPPH), thiobarbituric acid reactive species (TBARS), lipid peroxidation (LPO), and total antioxidant capacity (TAC) assays were used to determine the in vitro antioxidant activity of aqueous, n-butanol, ethyl acetate and hexane fractions of C. afer leaf and stem. RESULTS Proximate analysis revealed that the carbohydrate content was highest in the leaf (55.83 ± 3.71%) and stem (50.38 ± 1.27%) while crude fat content was lowest in the leaf (1.83 ± 0.43%) and stem (1.75 ± 0.48%). The minerals detected in appreciable quantity in both the leaf and stem samples were calcium, magnesium, potassium, sodium, chromium, lead, manganese, nickel, and copper. Further study showed that the aqueous leaf fraction exhibited a significantly (P < 0.05) high DPPH scavenging activity (IC50 = 259.07 µg/ml) and TAC (7.95 ± 0.37 mg ascorbic acid equivalent/g) compared with the other test fractions while the aqueous stem fraction had the highest TBARS scavenging activity (IC50 = 0.37 µg/ml) and inhibition of LPO (IC50 = 41.15 µg/ml) compared with the other test fractions. CONCLUSION The findings from this study indicate that C. afer could serve as a source of nutrient and minerals for animal nutrition and human metabolism. It also showed that the aqueous fractions of C. afer leaf and stem possess high antioxidant activity than the other fractions. In addition, this study may also explain the folkloric use of crude C. afer leaf or stem extracts in the treatment of oxidative stress associated diseases, including rheumatoid arthritis and hepatic disorder.