ISI 08-3e Determination of Fibre in Starch as Fibre Number

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1. Scope	The method is applicable to native potato and cassava starch	LT 1965 Rev. LT 30. Jan. 2000
2. Principle	Starch is hydrolysed and filtered. The discoloration of the filter is visual judged and compared with an internal standard scale.	Corns starches do not filter properly.
3. Apparatus	3.1 Analytical balance weighing to the nearest 100 mg.
	3.2 Boiling water bath.	Shaking bath convenient
	3.3 Vacuum filter with an active filter area 20 mm in diameter +   high flux paper filter.	The diameter of the active filter area is essential. Whatmann No. 1 35 mm diameter Cat. No. 1001 035
4. Reagents	4.1 Hydrochloric acid 0.1 N
	4.2 Colour plate Carry out the procedure on starch samples containing x ppm insoluble residues on dry matter with x ranging from 100 to 2000. Mark the filter paper with fibre number = x /500 and keep for reference.	The procedure is carried out with increasing quantity of same starch. Above 2.5 g the quantity of acid is increased proportionally.
5. Procedure	2.5 g sample as is is slurried in a conical flask with 30 ml acid (4.1)	Use 100 ml flask or larger
Hydrolysis	Place flask in boiling water bath (3.2) for 20 min	Shake min. until starch is gelatinised
Filtration	Filter hot on vacuum filter (3.3). Flush flask and filter with hot water.	Filtration flux must be quick
	Dry filter at max 105 oC
Judgement	Compare the visual appearance of the filter with the colour plate and assign by interpolation the fibre number of best fit.	A photometer may be used.
6. Reporting	Report fibre number of sample as is by averaging results of two samples with one decimal.
7. Notes	Fibre number is useful as internal standard. By reproduction of the colour plate the initial colour plate should be used for reference securing continuity rather than from a new independent impurity series. The diameter of the active filter area is essential.	Applying fibre numbers prevent confusion with determination of impurities by weight.
8. Image		Sartorius  filter funnel(min 30 ml) with glass vacuum holder for 35 mm  filters (20 mm diameter of active filter area), with PTFE-coated steel screen filter support. This support is essential to maitain a high flux.