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AACC International Approved Methods - AACC Method 32-40.01. Resistant Starch in Starch Samples and Plant Materials

AACC International Approved Methods

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AACCI Method 32-40.01
Resistant Starch in Starch Samples and Plant Materials

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Objective
The procedure described here can be used for the measurement of the resistant starch (RS) content of plant materials, food products, and commercial starch samples. (See Note 1.) The range of applicability of the test is 2-64% RS. The method is not suitable for samples with less than 1% RS (e.g., regular maize starch, which is 0.6% RS), although an indicative result is possible. For such samples, relative standard deviation values for repeatability (RSDr) and for reproducibility (RSDR) are high. In principle, samples are incubated in a shaking water bath with pancreatic alpha-amylase and amyloglucosidase (AMG) for 16 hr at 37°, during which time nonresistant starch is solubili1zed and hydrolyzed to glucose by the combined action of the two enzymes. The reaction is terminated by the addition of an equal volume of aqueous ethanol or industrial methylated spirits (IMS), and the RS is recovered as a pellet on centrifugation. This is then washed twice by suspension in aqueous ethanol or IMS (50% v/v), followed by centrifugation. Free liquid is removed by decantation. RS in the pellet is dissolved in 2M KOH by vigorously stirring in an ice-water bath over a magnetic stirrer. This solution is neutralized with acetate buffer, and the starch is quantitatively hydrolyzed to glucose with AMG. Glucose is measured with glucose oxidase/peroxidase reagent (GOPOD), and this is a direct measure of the RS content of the sample. Nonresistant (solubilized) starch can be determined by pooling the original supernatant and the washings, adjusting the volume to 100 ml, and measuring the glucose content with GOPOD.