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Apparent amylose content
Amylose content strongly influences the cooking and eating characteristics of rice. Amylose is responsible not only for the way cooked rice hardens on cooling (retrogradation) but also for its firmness and stickiness. These properties dictate consumer preference for different varieties of rice. Therefore, amylose is used as an important indicator of cooking and processing qualities.
Rice sample is ground to very fine flour using cyclone mill. Sodium hydroxide and ethanol are added to a test portion of the sample and the mixture is heated in a boiling water bath for 10 minutes. An aliquot of the test solution is then mixed with acetic acid and iodine solution to form blue starch-iodine complex and its absorbance (peak height) is measured at 620 nm using a colorimeter (continuous flow analyzer).
Since amylopectin is a known interference because it also forms complex with iodine, “apparent amylose” is used to define the analyte that is being measured by this method.
Note: For amylose content determination, the sample weight required is at least 2 g of rice flour placed in a paper bag. In order to keep the integrity of the customers' samples, senders are requested to place them in secured plastic boxes.
Juliano BO. 1971. "A simplified assay for milled-rice amylase." Cereal Science Today 16 (10): 334-340.
International Organization for Standardization. 2015. ISO 6647-1: 2015 Rice-Determination of amylose content-Part 1. Reference method. pp. 1-4.
Sreenivasulu, N. (2018). Rice Grain Quality: Methods and Protocols. New York, NY: Humana Press.