Determination of the Pentosan Content of Wheat Products by Hydrolysis, Glucose Oxidase Treatment and Analysis by HPAEC/PAD

Abstract

Abstract A method was developed for determining routinely the total pentosan content of wheat flour, commercial B-starch and gluten. In this method, the polysaccharides in the sample were hydrolysed by treatment with 2 m HCl at 100°C. The resulting pentosan monosaccharides were characterised by anion-exchange chromatography (HPAEC) combined with pulsed amperometric detection (PAD). Using this method, water-extractable pentosans can be determined with only minor adjustments. Interference by the relatively high concentration of starch-derived glucose in the sample, in the HPAEC separation of the pentosan monosaccharides, was eliminated by enzymic conversion of glucose into gluconic acid using glucose oxidase (GOD). Efficient removal of glucose (1 h incubation time) required a relatively high amount of GOD and a continuous supply of oxygen into the solution. The activity of GOD against galactose and xylose was subsequently blocked by lowering the pH of the sample to about 1. The method described has good repeatability. The standard deviation in the pentosan content (sum of the pentose sugars arabinose and xylose) was less than 0·1% for flour, B-starch (pentosan content about 2%) and gluten (pentosan content of about 1%).