ISI 38-3e Determination of Cold Water Solubles by Viscometer


1. Scope The method is applicable to commercial starch.

 

 Jan 1990 rev. Nov. 2002
2. Principle Viscosity of the water phase of a slurry is interpreted as concentration of cws

 

 cws = cold water solubles
3. Apparatus 3.1 Brookfield viscometer RVT

 
4. Procedure Weigh a starch sample w g as is containing 50 g starch dry matter to the nearest g. Add distilled water at ambient temperature to a total of 200 g and stir for 30 minutes. Equivalent to 21 degree Beaumé starch slurry.
The starch is allowed to settle and the viscosity of the supernatant is measured with the instrument (3.1) and the reading (v) in cps is recorded.

 

 cps = centipoise

Spindel no. 2 and 60 RPM
5. Calculation Report reading as cps without decimals or
report with two decimals as cws% as is = 0.0072*v - 0.32

 

 Check equation and correct if necessary
6. Note The viscosity method is fast and simple. The expression of viscosity as cws is more expressive, but it is compulsory to attach the method designation to the result. 

Alternative: Filter the sample slurry and dry 50 g of filtrate at 130 oC and calculate the solubles as percentage of sample dry matter.

By expression as cws the correlation of viscosity to starch solubles determined by a more direct method should be checked at various levels of cws and found significant. 

The method is developed in the potato starch industry. Viscosity determination depends on preparation and sample history. It is therefore advisable to check the equation for use in a particular laboratory and correct  if necessary.

Standarddeviation on the difference  should be better than. 0.03% cws

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