QUANTITATIVE MEASUREMENT OF TOTAL STARCH IN CEREAL FLOURS AND PRODUCTS

A rapid and quantitative method has been developed for the determination of total starch in a wide range of materials, including high-amylose maize starches and food materials containing resistant starch. The method allows the analysis of 20 samples in 3 h. A single assay can be performed in 2 h. For a range of samples, the total starch values obtained with this method were significantly higher than those obtained with current standard methods. Two assay formats have been developed. In assay format 1, the sample is incubated solubilised with the chaotropic agent dimethyl sulphoxide (DMSO) to gelatinise the starch, which is then solubilised and partially depolymerised by controlled incubation at ∼ 100°C with a defined level of thermostable alpha -amylase. This allowed near-complete solubilisation of most starches. The remaining starch is then solubilised and the starch fragments are converted to maltose and maltotriose by the combined action of highly purified pullulanase and beta-amylase. After volume adjustment and filtration (if necessary), the maltooligo-saccharides are hydrolysed by high-purity amyloglucosidase to glucose, which is measured with a glucose oxidase/peroxidase reagent. This assay format gave quantitative starch determination in all native starch samples, including high-amylose maize starches. In assay format 2, which is applicable to most starches and cereal flours, the DMSO pre-treatment step is omitted. Samples containing glucose and/or maltosaccharide are pre-washed with aqueous ethanol before analysis. © 1994 Academic Press Limited.