Enzymic determination of starch in samples with high sugar content

Starch may be determined by hydrolysis with α-amylase and amyloglucosidase followed by specific measurement of glucose using glucose oxidase. However biological samples to be analysed for starch often also contain glucose, maltose and higher oligosaccharides derived from the hydrolysis of starch. These sugars may be difficult to remove quantitatively by solvent extraction. We have found that reduction with sodium borohydride followed by evaporation with 2,2 dimethoxypropane removed interference from glucose, maltose and the two reducing terminal residues from higher oligosaccharides. The specific glucose test was not sensitive to glucitol produced by reduction of free glucose. Maltitol was not hydrolysed significantly by the amyloglucosidase, removing interference from maltose and the two reducing terminal residues from higher polymers. The method has potential for monitoring the hydrolysis of starch especially in the mobilisation of starch reserves in plant tissues such as in the endosperm of germinating cereal grains. A reduction ratio based upon the method is proposed for use in characterising starch hydrolysates