ISI 13-2e Determination of Starch in Tubers by Under Water Weight

ISI 13-2e Determination of Starch in Tubers by Under Water Weight



1. ScopeThe method is applicable to potato and cassava.

For cassava roots it is important to note that the results can easily be compromised by air taken up in the roots

LT 1986
Rev. LT 31. Dec. 1997
Rev. LT 18. March 2019
2. PrincipleDetermination of under water weight of 5050 g tuber & roots

 

3. Apparatus3.1 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. ProcedureSuspend 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.

 TARA

Weigh TARA HIGH (To) of rod and empty basket to the nearest 0.1 g.

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.

 Tubers

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

 

Completely immersed
5. CalculationCalculate starch as starch dry matter of sample as is and report with one decimal.

 Dry sample

Starch % = 5050 * 0.051738 ((Wu - Tu) / (Wo - To)) - 5.2463Clean and dry tubers

 Wet sample

Starch % = 5050 * 0.051738 ((Wu - Tu) / (0.98 (Wo - To))) - 5.2463

 

Correcting tuber weight 2% if wet
6. NotesIn 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 1996

 

  EU-method
8. Image
The picture reproduces better when printed than on the web screen
 

The EU-method is valid for potatoes within a range of 13-23 % starch dry matter.

This range in this graph is extended to 35% starch dry matter by extrapolation.

If the analytical method is used on cassava roots, the results can be compromised by air taken up in the roots.

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