Abstract:
Studies on the starchy tubers of the plant Dioscorea polystachya have recently attracted attention due to the numerous promising health benefits which have been reported. These include, but are not limited to, the possession of anti-cancer, anti-diabetic and anti-obesity agents along with a possible attribute that reduces high blood pressure and hypolipidemia. Dioscorea polystachya has been used as an important ingredient in traditional Chinese herbal medicine in improving kidney function and meliorating discomfort in the digestive system. In addition, there is growing interest in using D. polystachya starch in related food processing. In addition to containing abundant starchy, Dioscorea polystachya tubers contain a slimy mucilage. However, the prcise composition of this and the cell walls which contribute dietary fiber is not known. The objective of the current study was to develop a suitable approach to extract the mucilage from the tubers of D. polystachya while minimizing contamination from starch and the contents of the cell walls. The current study focuses on analysing the cell-walls and the mucilage contained in the cells of D. polystachya tubers. The mucilage was obtained by extracting the cubes of D. polystachya tubers with boiling sodium maleate buffer (pH 6.0) for 10 mins. After three extensive treatments with a combination enzymes of α-amylase and amyloglucosidase, starch was successfully removed from the mucilage preparation. Protein contributed more than half of the dry weight (51.8 % w/w) of the mucilage preparation and water soluble polysaccharides contributed approx 20 % (w/w). The results indicated the presence of glucomannan or galactoglucomannan in the mucilage of D. polystachya. Mannose contributed more than half of the neutral monosaccharide content of the mucilage with smaller amounts of glucose, galactose, arabinose, rhamnose and xylose. In contrast, the predeminent nono-cellulosic monosaccharide in the cell walls was galactose followed by xylose, glucose, rhamnose, arabinose, fucose and mannose. This indicated the cell walls contain large amounts of pectic polysaccharides consistent with this species being a non-commelinid monocotyledon and having a composition resembling that of unlignified primary cell walls of some eudicotyledons. No arabinogalactan proteins were detected in the tissue of Dioscorea polystachya using the Yariv reagents.