Study on Carbohydrate Composition of Apios (Apios americana Medikus) Flowers and Tubers

Abstract

Carbohydrate composition in the tubers and flowers of apios (Apios americana Medikus) were investigated. The approximate mono- and oligosaccharide, starch and cell-wall polysaccharides content per 1g triturated samples were 188mg : 479mg : 36mg for tubers, and 192mg : 179mg : 131mg for flowers, respectively.
Analysis of the mono- and oligosaccharide fractions by gel-filtration chromatography and high-performance anion-exchange chromatography showed that 86-90% of the fractions from tubers were glucose and sucrose and most of the fractions from flowers were glucose and fructose. In addition, 14-10% of the fractions from tubers were oligosaccharides with degrees of polymerization exceeding 3, including raffinose and stachyose. Scanning electron microscopy of starch granules isolated from apios tubers revealed that they were egg-shaped and approximately 10.6μm in size.
The cell walls of tubers and flowers contained pectic compounds, hemicellulose and cellulose at a ratio of 6 : 43 : 51 and 7 : 36 : 56, respectively.
The results of the methylation analysis of these polysaccharide fractions indicated presence of rhamnogalacturonan as well as the neutral sugars, arabinan, xylan, galactan, arabinogalactan, xyloglucan and cellulose in the cell walls of tubers and flowers.
The findings were discussed relative to the carbohydrate concentrations in the soybean, azuki bean, potato and sweet potato.