International Starch Institute. ISI 35 Determination of Reductive Power in Starch.

Home	Profile	Market Place	Sweeteners	Lab Methods	Glossary	Search
Master Index	Environment	Application	Starch	Statistics	Tables	Write us

International Starch Institute
Science Park Aarhus, Denmark
ISI 35-1e Determination of Reductive Power in Starch

1. Scope	The method is applicable to thin-boiling starch	LT 18.12.1964 Rev. 17.03.1998
2. Principle	Ferric cyanide is reduced by starch to ferrous cyanide and precipitated as a zinc compound. Excess ferric ions reduce J^- and iodine is titrated with thiosulphate.
3. Apparatus	3.1 Analytical balance weighing to the nearest 1 mg. 3.2 Boiling water bath 3.3 Erlenmeyer flask 300 ml 3.4 Kjeldahl bulb
4. Reagents	4.1 Alkaline ferric cyanide solution 0.05M: 16.5 g K₃Fe(CN)₆+ 22 g water free Na₂CO₃ ad one litre distilled water. Keep dark. 4.2 Zinc solution: 200 ml water free acetic acid, 70 g KCl and 20 g ZnSO₄, 7H₂O ad one litre with distilled water
	4.3 Potassium iodine KJ
	4.4 Thiosulphate 0.05N: 50.0 ml	Short shelf life
5. Procedure	Weigh approximate 250 mg (g) sample to the nearest mg and transfer to 300 ml flask (3.3). Slurry in 25 ml distilled water.
	Gelatinise on boiling water bath for 5 min.
	Add with one mark pipette 25.0 ml alkaline ferri cyanide (4.1) under agitation. Cover flask with Kjeldahl bulb and place in vigorously boiling water bath for 15 min. Then rapidly cooling under tap.
	Ad from graduated beaker 60 ml zink solution (4.2). Shake and add approx. 4 g KJ (4.3)
Titration	Free iodine is titrated with thiosuplphate (4.4)
Blank	Run a blank with 25 ml distilled water without heating.

6. Calculation	Calculate reducing power of sample dry matter by averaging results of two samples with two decimals. Reducing Power, R_Cu = mg copper per g starch dry matter = ((b-a) x 1000 x N x 6.354) / (g x d ), where a = ml thiosulphate for titration of sample b = ml thiosulphate for titration of blank N = Normality of thiosulphate g = g sample d = % dry matter of sample
6. Note	Reducing power is also expressed as a ferric cyanide number, Fecy = ml 0.1 N thiosulphate per g starch dry matter. The R_Cu / Fecy is a measure for reducing groups in sample and groups formed during analysis.
7. Reference	Schoch; Methods in Carbohydrate Chemistry, Vol. IV, 64 (1964)

| Top of Page | LabIndex |

Copyright^© 1999. Read Disclaimer notice.
All rights reserved. International Starch Institute, Science Park Aarhus, Denmark.

Keywords: laboratory method determination reductive power reducing thin-boiling starch