Antioxidative activity of water hyacinth components

The antoxidative properties of water hyacinth leaves were investigated by evaluating the scavenging capacity of liquid extracts in a competitive protective process against oxygenated free radicals (OFRs) released via electrolysis in a phosphate buffer with a Pt electrode. Colorimetric measurements carried out at 515 nm, through a N,N-diethyl-1,4-phenylenediamine (DPD) assay, showed a decreased absorbance of the sample, as compared to the blank obtained by electrolysis of the buffer without plant extract, revealing, thereby, the presence of antioxidizing agents in the liquid extracts. The antioxidative activity was estimated in terms of equivalent-glutathione (EG, in nmoles equivalent-glutathione per gram of dry plant material selected (eg/gdp)), and compared to those of soya beans and garlic bulbs. The EG value increased with decreasing dilution factors, regardless to the plant type, suggesting a strong influence of the medium pH on the antioxidizing agent extraction yields. Various plant drying procedures, namely: sunlight exposure (at 25-30degreesC), heating (40 and 60degreesC) and freeze-drying (at -70degreesC) were also examined. The highest EG (ca. 40 nmol eg/gdp) was observed for freeze-dried leave extract, while the lowest value was obtained upon heating at 60degreesC (16-17 nmol eg/gdp), presumably due to a detrimental effect of increased temperature. The glutathione content in the plant extracts was further determined spectroscopically at 412 nm, through an enzymatic assay, using glutathione reductase. Small but interesting contents of glutathione (ca. 40 nmol eg/gdp) were found in the hyacinth leaves, making this plant to be regarded as an alternative and convenient low-cost raw material for antioxidizing agent recovery. (C) 2003 Elsevier Ireland Ltd. All rights reserved.