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76 Starch Methods​

76-11.01 Starch—Glucoamylase Method with Subsequent Measurement of Glucose with Glucose Oxidase

Starch is measured as glucose by an enzymatic-colorimetric assay, after initial gelatinization in an autoclave, followed by enzymatic hydrolysis. This method is applicable to starch determination in complex media, including all starchy products (food and feed, digestive contents) and glycogen. See Note 1.

76-13.01 Total Starch Assay Procedure (Megazyme Amyloglucosidase/alpha-Amylase Method)

This method describes determination of total starch in cereal products using a kit sold by Megazyme International Ireland Ltd. (Bray, Ireland). For samples that do not contain high levels of resistant starch (e.g., wheat flour), complete solubilization of starch is achieved by cooking the samples in the presence of thermostable alpha-amylase followed by amyloglucosidase hydrolysis to glucose. Samples that contain high levels of resistant starch (e.g., high-amylose maize starch) are completely solubilized by pretreatment with dimethyl sulfoxide at 100°C, followed by thermostable alpha-amylase treatment. The maltodextrins are hydrolyzed to glucose with glucoamylase, and the glucose produced is measured using glucose oxidase/peroxidase reagent. Samples containing high levels of glucose or maltodextrins are washed with aqueous ethanol before analysis. Analysis of a single sample can be completed within 70 min. Twenty samples can be completed within 2 hr.

76-21.02 General Pasting Method for Wheat or Rye Flour of Starch Using the Rapid Visco Analyser

The objective of this method is to prepare a complete pasting curve, including initial pasting, maximum viscosity, breakdown, and setback, during heating in excess water. The method relies upon the change in rotary viscosity that occurs when starch granules hydrate, swell, and ultimately disintegrate, followed by possible realignment of the starch molecules during cooling. In addition to inherent paste viscosity, the method monitors the liquefying action of alpha-amylase, which may be present as an intentional additive or as a result of sprout damage. Maximum viscosity before the onset of cooling (peak viscosity), time to peak viscosity, minimum viscosity after peak, and final viscosity provide indications of the pasting properties of the sample and hence its processing value for baking and other purposes. This method is applicable to cereal flours and pure starches.

76-22.01 Pasting Properties of Oat—Rapid Viscosity Analysis

This is a method to determine the paste viscosity characteristics of milled oat flour and wholemeal flour. These characteristics, which are predictors of oat processing properties, are obtained by simultaneously heating and stirring an aqueous suspension of ground oat flour or wholemeal in a disposable canister placed in a Rapid Visco Analyser. A precisely controlled heat-hold temperature profile is used to cause viscosity changes in the mixture.

76-30.02 Determination of Damaged Starch

Starch granules in wheat endosperm may be damaged during milling. This alters flour water absorption and dough mixing properties. This method determines the percentage of starch granules in flour or starch preparations that is susceptible to hydrolysis by fungal alpha-amylase. Percent starch damage is defined as g starch subject to enzymatic hydrolysis per 100 g sample on a 14% moisture basis.

76-31.01 Determination of Damaged Starch—Spectrophotometric Method

Some starch granules of flour are damaged during milling of wheat, and the degree of damage affects water absorption and dough mixing characteristics of the resulting flour. In this method, damaged starch granules are hydrated; this is followed by hydrolysis to maltosaccharides and limit dextrins by fungal alpha-amylase. Amyloglucosidase is then used to convert dextrins to glucose, which is specifically determined spectrophotometrically after glucose oxidase/peroxidase treatment. Damaged starch is calculated as a percentage of flour weight on "as is" basis. This method is applicable to wheat flour and starch.

76-33.01 Damaged Starch — Amperometric Method by SDmatic

Damaged starch is a very important flour quality parameter because it affects water absorption. To determine the extent of starch damage, this method measures the kinetics of iodine absorption in a liquid suspension, using an amperometric probe. Results are given in an iodine absorption index percentage (AI%). An indication of the speed of iodine absorption in seconds is also reported as “Vabs”. The method is specific to white flour obtained from Triticum aestivum coming from either laboratory or industrial milling, but it can also be used on wholemeal flour.