Discussion 712 Determination of starch by acid hydrolysis

The official EC method for starch in feeding stuffs is document 374L0203 (which is presented in the Official Journal No. L1 08, 22.04.74, pp. 7-24), and is the Fifth Commission Directive 74/203/EEC of 25 March 1974. The determination of starch appears as Annex I to the Directive. The AOAC gives an involved titrimetric method for starch in plants (Isaac, 1990, p. 60) and refers to older editions for starch in animal feed, including a direct hydrolysis method (Padmore, 1990, pp. 83-84). We will describe a method developed for starch in potatoes, but it may be used with other plant materials (Faithfull, 1990). See the discussion on the extraction procedure in Chapter 4, 'Fibre, lignin, cellulose, nitrogen-free extract and starch'. The starch is hydrolysed to glucose by heating with M HCl, which is then determined by autoanalysis using a colorimetric anthrone procedure. Correction factors are necessary to allow for the water content of the starch which remains after oven drying, for conversion of starch residue units of C6H10O5 to the higher molecular mass units of glucose, C6H12O6, and also for the conversion of any plant cell walls to chromogenic products.

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