BS EN ISO 6647-1:2020 pdf download.Rice – Determination of amylose content.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
amylose
DEPRECATED: apparent amylose
polysaccharide constituent of starch, the macromolecules of which have glucose units linked in a
predominantly linear structure
3.2
amylopectin
polysaccharide constituent of starch, the macromolecules of which have from 6 to 100 linked glucose units in a branched structure
4 Principle
Rice is ground to a very fine flour to break up the endosperm structure in order to aid complete
dispersion and gelatinization; the flour is then defatted. A test portion is dispersed in a sodium
hydroxide solution. An aliquot portion is taken to which an iodine solution is added. The absorbance, at 720 nm, of the colour complex formed is then determined using a spectrophotometer.
The amylose mass fraction of the sample is then read from a calibration graph, which is prepared using mixtures of potato amylose and amylopectin to make allowance for the effect of amylopectin on the colour of the amylose–iodine complex of the test solution.
5 Reagents
Use only reagents of recognized analytical grade, unless otherwise specified, and distilled or
demineralized water or water of equivalent purity.
5.1 Methanol, a volume fraction of 85 %.
5.2 Ethanol, a volume fraction of 95 %.
5.3 Sodium hydroxide, 1 mol/l solution.
5.4 Sodium hydroxide, 0,09 mol/l solution.
5.5 Detergent solution.
Dissolve sodium dodecylbenzene sulfonate corresponding to a concentration of 20 g/l. Just before use, add sodium sulfite to a final concentration of 2 g/l.
5.6 Sodium hydroxide, for protein removal, 3 g/l solution.
5.7 Acetic acid, 1 mol/l solution.
5.8 Iodine solution.
Weigh, to the nearest 5 mg, 2,000 g of potassium iodide in a weighing bottle fitted with a stopper. Add sufficient water to form a saturated solution. Add 0,200 g of iodine, weighed to the nearest 1 mg. When all the iodine has dissolved, transfer the solution quantitatively to a 100 ml volumetric flask (6.6), make up to volume with water and mix.
Prepare a fresh solution on each day of use and protect it from light.
5.9 Stock potato amylose suspension, free of amylopectin, 1 g/l.
5.9.1 Defat the potato amylose by refluxing with methanol (5.1) for 4 h to 6 h in an extractor at a rate of 5 to 6 droplets per second.
The potato amylose should be pure and should be tested by amperometric or potentiometric titration.
Some commercial preparations are impure and would give erroneously high results for the amylose mass fraction of rice samples. Pure amylose should bind 19 % to 20 % of its own mass of iodine. For checking the purity of amylose, see Annex A.
5.9.2 Spread the defatted potato amylose on a tray and leave for two days to allow evaporation of residual methanol and for moisture content equilibrium to be reached.
Treat the amylopectin (5.10) and the test samples (see 8.1) in the same way.BS EN ISO 6647-1 pdf download.