Phenolic Composition and Antioxidant Capacity of Biomass Residue (Leaves) Generated from Bambusa tulda Plantations

Bambusa tulda (BT) plantations generate vast quantity of leaves as biomass residue during harvesting of poles which are of no commercial value and remain underutilized. Possibility of valorization of this biomass residue for development of natural antioxidants was examined. Eight different extracts of the fresh and shade dried BT leaves using methanol and methanol: water (4:1, v/v) under Soxhlet and at room temperature were prepared and evaluated for their yield, total phenolic contents (TPCs, mg GAE/g of extract), total flavonoid contents (TFCs, mg quercetin equivalent/g extract), total antioxidant capacity employing DPPH. scavenging, reducing power, hydroxyl radical scavenging and metal chelating assays. Hot methanol: water (4:1) extract of the fresh leaves exhibited the highest yield (22 %), TPCs (221), TFCs (135) and total antioxidant capacity (EC50 values, DPPH. scavenging, 194 mu g/ml; reducing power, 1343 mu g/ml; hydroxyl radical scavenging, 466 mu g/ml; metal chelating, 2 mg/ml) and was further fractionated with petroleum ether, ethyl acetate, butanol and water. Ethyl acetate and butanol fractions showed significantly higher TPCs (679, 637), TFCs (156, 119) and potent antioxidant activity in the above assays. A total of 13 phenolic compounds (7 phenolic acids, 5 flavones and 1 flavonol) with varied distribution in these fractions were characterized using HPLC-ESI-QTOF-MS. A significant correlation was found between phenolics and antioxidant capacity as well as within the various antioxidant assay methods. The findings suggested the use of Bambusa tulda leaves as a potential natural source of antioxidants.