International Starch Institute: Determination of Starch in Potatoes

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

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.

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. The extrapolated values are not enforced by the EU.

W_o ¹ g	W_u² 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
Extrapolation:
5050	557	1,124	23,7%
5050	569	1,127	24,3%
5050	581	1,130	25,0%
5050	593	1,133	25,6%
5050	605	1,136	26,3%
5050	616	1,139	26,9%
5050	628	1,142	27,6%
5050	640	1,145	28,2%
5050	651	1,148	28,9%
5050	663	1,151	29,5%
5050	674	1,154	30,8%
5050	697	1,160	31,5%
5050	708	1,163	32,1%
5050	719	1,166	32,8%
5050	730	1,169	33,4%
5050	741	1,172	34,1%
5050	752	1,175	34,7%

¹) Weight of potato sample above water. ²) Weight of sample immersed in water. ³) Calculated density = (W_o / (W_o -W_u)). 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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