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International Starch Institute
Science Park Aarhus, Denmark
Determination of Starch in Potatoes according to EU-direction

 Density

The starch content of fresh potatoes is correlated with potato density. A sample of 5050 g potato in a net basket is weighed above water and then again immersed in clean water of maximum 18 oC.

Wo = weight of the potato sample

Wu = weight of sample under water

Density dpotato = Wo / (Wo - Wu) g/ml

Starch dry matter = (dpotato -1.01506) / 0.0046051 %

The calculated figure in per cent deviate less than 0.05 from values read out of the EU-table enforced by the European Commission covering potatoes with 13% to 23% starch dry matter. The full table as per 17 January 1995. A short version of the table - valid per 1. July 1996 - is as follows:

 

Wo 1

g

Wu 2

g

Density d 3

g/ml

Starch dry matter of potatoes 4

%

Potatoes to produce 1 t commercial starch 5

kg

EU-minimum price 6

ECU/t potato

EU-subsidy I to the factory 7

ECU/t potato

EU-subsidy II to the factory 8

ECU/t potato

5050

352

1.075

13

6,533

32.11

3.405

13.31

5050

371

1.079

14

6,089

34.45

3.659

14.28

5050

392

1.084

15

5,664

37.04

3.924

15.35

5050

411

1.089

16

5,327

39.38

4.178

16.32

5050

430

1.093

17

5,000

41.96

4.456

17.39

5050

450

1.098

18

4,720

44.44

4.709

18.42

5050

469

1.102

19

4,481

46.82

4.963

19.40

5050

488

1.107

20

4,299

48.80

5.180

20.22

5050

508

1.112

21

4,234

49.55

5.253

20.53

5050

527

1.117

22

4,140

50.67

5.373

21.00

5050

545

1.121

23

4,056

51.72

5.482

21.43

 

1) Weight of potato sample above water. 2) Weight of sample immersed in water. 3) Calculated density = (Wo / (Wo -Wu)). 4) Starch content according to the official table. 6) The minimum price to be paid by the manufacturer directly to the farmer in order to qualify for a subsidy. 7) An EU-subsidy I- a production premium - is paid to the manufacturer, if he pays the EU-minimum price or better. 8) A subsidy II- an equalisation payment - is paid directly to the factory, if he pays the EU-minimum price or better. The exchange rate 1. July 1996 was 1 ECU = 1,24 US$.

This empirical method is used to settle accounts with suppliers of potatoes to starch factories. Similar method is used for cassava. Unfavourable storage conditions however may cause enzymatically conversion of starch to glucose affecting starch yield without changing the under-water-weight and density of potatoes. Therefore the method only apply to fresh potatoes. The method is by no means scientifically correct. Reliable methods for the determination of carbohydrates in potatoes exists, but the soluble non-starch fraction and the fraction of particular starch grains are indistinguishable from one another by practical accurate means.


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Keywords: laboratory method determination starch potato