Methodology for Carbohydrates
Determination of amylose
Starch is composed of two components, namely amylose and amylopectin. Amylose is a linear or non-breanched polymer of glucose. The glucose units are joined by a-1-4-glucosidic linkages. Amylose exist in coiled form and each coil contains six glucose residues.
The iodine is adsorbed within the helical coils of amylase to produce a blue colored complex which is measured colorimetrically.
- Distilled water
- 1N NaOH
- 0.1% phenolphthalein
- Iodine Reagent: Dissolve 1g iodine and 10g KI in water and make up to 500mL.
- Standard: Dissolve 100mg amylase in 10mL 1 N NaOH; make up to 100mL with water.
- Weigh 100mg of the powdered sample, and add 1mL of distilled ethanol. Then add 10ml of 1 N NaOH and leave it overnight.
- Make up the volume to 100ml.
- Take 2.5ml of the extract, add about 20ml distilled water and then three drops of phenolphthalein.
- Add 0.1 N HCl drop by drop until the pink color just disappears.
- Add 1ml of iodine reagent and make up the volume to 50ml and read the color at 590nm.
- Take 0.2, 0.4, 0.6, 0.8 and 1ml of the standard amylase solution and develop the color as in the case of sample.
- Calculate the amount of amylose present in the sample using the standard graph.
- Dilute 1ml of iodine reagent to 50ml with distilled water for a blank.
Absorbance corresponds to 2.5ml of test solution = ‘x’ mg amylose
100 ml contains = (‘x’ ÷ 2.5) × 100mg amylose = % amylose
- The sample suspension may be heated for 10min in a boiling water bath instead of overnight dissolution.
- The amount of amylopectin is obtained by subtracting the amylose content from that of starch.
- McCready, R M, Guggolz, J, Siliviera, V and Owens H S (1950) Anal Chem 22 1156.
- Juliano, B O (1971) Cereal Sci Today 16 334.
- Thayumanavan, B and Sadasivam, S (1984) Plant Foods Hum Nutr 34 253.