Phenolic compound content, antioxidant and radical-scavenging properties of methanolic extracts from the seed coat of certain thai tamarind cultivars

Methanolic extracts from the seed coats of five major tamarinds (Srichomphu, Sithong-nak, Sithong-bao, Priao-yak and Khanti) cultivated in Thailand were investigated for their content of phenolic compounds and their antioxidative properties. Antioxidative properties were evaluated by various different methods: scavenging effect on the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and hydroxyl radical, anti-lipid peroxidation and reducing power assay. The phenolic compound contents were determined by spectrophotometric methods. Extract of Priao-yak with the highest tannin content showed the strongest reducing power, while extract of Khanti with the highest proanthocyanidin content revealed high scavenging ability on both DPPH and hydroxyl radicals. Stronger antioxidative activity measured by most assays was noted for the extract of Sithong-bao with a high content of total phenols, proanthocyanidin and tannins. The results suggest that specific phenolic constituents in the extract could be responsible for the different antioxidant properties observed in different cultivars. Furthermore, seed coat extract of Sithong-bao may be a potential source of natural antioxidant to be developed into nutraceuticals. Components of Tamarindus indica L., a tree indigenous to India and South-East Asia, have long been used as a spice, food component and traditional medicine. According To traditional medicine, the tamarind pulp is used as a digestive, carminative, laxative, expectorant and blood tonic; the seeds are used as an anthelmintic, antidiarrheal and emetic. In addition, the seed coat is used to treat burns and aid wound healing as well as as an antidysenteric. Recent studies have demonstrated polyphenolic constituents with more potent antioxidant and anti-inflammatory activities of T. indica seed coat extract. Therefore, seed coat extracts of T. indica have economic potential for development into health promotion products as well as natural preservatives to increase the shelf life of food by preventing lipid peroxidation.