|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 22-1e Determination of Starch in Fruitwater by Ewers
|1. Scope||The method is applicable to potato and cassava fruitwater and fruitjuice
(Effluent from the extraction of starch from tubers)
|LT 18. Dec. 64
Rev. LT 11. Dec. 98
|2. Principle||Granular starch is hydrolysed and determined by Ewers polarimetric
|3. Apparatus||3.1 Analytical balance weighing to the nearest 1 mg.
3.2 Polarimeter with 2 dm tube
3.3 Shaking boiling water bath.
3.4 Volumetric flask, 100 ml with wide neck
3.6 Conical glass beaker, 1500 ml with rack
|4. Reagents||4.1 Dilute hydrochloric acid 0.12 N
4.2 Lead solution, saturated.
Dissolve 70 g Pb(CH3COO)2, 3 H2O in 100 ml hot distilled water.
|Leave to stand for sedimentation of excess acetate.|
|5. Procedure||Collect a 1000 ml sample (v1).|
|Centrifuge sample or let leave it to precipitate in a conical beaker (3.6). Discard the supernantant. Stir sediment with distilled water and (repeat) centrifugation.||It is essential to remove residual juice.|
|Collect the starch containing sediment and transfer to volumetric flask (3.4) and flush down sample with 60 ml diluted hydrochloric acid (4.1).|
|Place volumetric flask in boiling water bath (3.3) for 15.0 min||Shake min. 3 min initially|
|Cool flask in cold water to 20 oC. Add 4 ml lead solution (4.2). Fill to mark with water. Shake and leave to stand for 45 min.||Cool rapidly|
|Filter through funnel and paper.||Repeat with more lead solution if not clear|
|Measure optical rotation (a1) of
the filtrate with the polarimeter (3.2)
|6. Calculation||Starch in percent of sample as is (average results of two samples
with two decimals) =
Starch % = 1000000 *a 1 / (a D*2*v1)
|Value of a D at
589.3 nm for starch from:
potato = +185.7
cassava = +184.0
|7. Notes||Proper wash of isolated sediment and proper clarification is essential. Alternative: Clarify with Carrez solutions.||Residual juice dims polarimeter readings|
|Quick method: Centrifuge15 ml sample in conical beaker with 0.1 ml marks.
Read (or estimate) starch sediment in ml (v2). Starch dry matter = v2*0.6
|Impurities often reduce readings to a rough estimate.|
|8. Reference||International Standard: ISO 10520|
| Top of Page | LabIndex |
Copyright© 1999. Read Disclaimer notice.
All rights reserved. International Starch Institute, Science Park Aarhus, Denmark.
Keywords: laboratory method determination starch potato cassava fruitwater fruitjuice juice Ewers