Abstract
An enzymic colorimetric micromethod for the determination of damaged starch in samples weighing 50 mg was used. Oligosaccharides in filtered fungal α-amylase digests of damaged granules were hydrolysed with amyloglucosidase to yield glucose which was measured with a glucose oxidase—peroxidase—chromogen reagent. Sixteen manual determinations were performed in 3 h, or 32 determinations in 3 h if automated flow injection analysis of the digests was used. A comparative study of the American Association of Cereal Chemists (AACC) and the Farrand methods, both of which determine damaged starch as reducing sugars by non-specific methods, provided evidence that the AACC method overestimates damaged and gelatinized starch by about 30 % (α-glucan basis), while the Farrand method gives corresponding values which are about three times greater. These methods quantify, as ‘maltose’, only 64–70 % of the starch digested by α-amylase, and substantial correction factors are then used to calculate the total damaged starch content. Since amylose contplexed with endogenous lipids of cereal starches is not digested by fungal α-amylase, a small correction factor should be used for damaged or gelatinized cereal starches; no correction is required for the lipid-free waxy cereal starches and non-cereal starches. The micromethod can also be used to quantify gelatinized starch in processed cereal foods.
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