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International Starch Institute
Science Park Aarhus, Denmark
ISI 13-2e Determination of Starch in Tubers by Under Water Weight
|1. Scope||The method is applicable to potato and cassava tubers.
Rev. LT 31. Dec. 1997
|2. Principle||Determination of under water weight of 5050 g tuber
|3. Apparatus||3.1 Underhanging balance
3.2 Stainless steel rod with two hooks. Distance between hooks = height of basket + approx. 10 cm.
3.3 Weighing net basket in stainless steel
3.4 Vessel with clean water of maximum 18 oC
|4. Procedure||Suspend rod (3.2) in underhanging balance (3.1).
Place basket (3.3) on upper hook of rod (3.2). Place vessel (3.4) below balance, rod and basket. Fill vessel with water a few cm below basket.
|Weigh TARA HIGH (To) of rod and empty basket to the nearest
Move basket to lower hook and weigh TARA LOW (Tu) to the nearest 0.1 g of rod and empty basket.
|Adjust hooks so basket is completely immersed in water on lower hook.|
|Weigh 5 kg clean tubers to the nearest 1 g (Wo) into basket (3.3) on upper hook.|
|Move basket with sample to lower hook and weigh again (Wu) to
the nearest 0.1 g
|5. Calculation||Calculate starch as starch dry matter of sample as is and report with one decimal.|
|Starch % = 5050 * 0.051738 ((Wu - Tu) / (Wo - To)) - 5.2463||Clean and dry tubers|
|Starch % = 5050 * 0.051738 ((Wu - Tu) / (0.98 (Wo
- To))) - 5.2463
|Correcting tuber weight 2% if wet|
|6. Notes||In stead of weighing 5050 g exactly and using a table as the official
method the above version is generally accepted.
|7. Reference||"Instruction no. 2 Mkt. 4410-4-96 of July 1996" issued by The
Danish EU-directorate, Ministry of Agriculture & Fishery enforced 1st July
|8. Image||The picture reproduces better when printed than on the web screen|
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