International Starch Institute
Science Park Aarhus, Denmark
Determination of Crude Fibre in Starch by Weight
Notes for ISI 09

1.1 600 ml beaker or digestion flask
1.2 Digestion apparatus  equipped with condenser for controlling the volume of solution during digestion
1.3 Filtering cloth or linen cloth, 200 mesh or number of number of threads per cm = 18 (45 threads per inch)
1.4 Gooch crucible or alundum crucible R-98
1.5 Electric air oven
1.6 Electric muffle furnace
1.7 Desiccator with desiccant

2 Reagents

2.1 0.255 N sulfuric acid (100 ml of this solution contains 1.25 g of acid)
2.2 0.313 N sodium hydroxide solution (100 ml of this solution contains 1.25 g of sodium hydroxide)
2.3 95% alcohol

3 Procedure

Transfer 2.5 g of the sample into the beaker (clause 1.1), add 200 ml of boiling sulfuric acid (clause 2.1), and connect it with the digestion apparatus (clause 1.2). Boil for exactly 30 minutes, filter through filtering cloth (clause 1.3) and wash with hot water until it is free from acid. Transfer the residue on the cloth into the flask with 200 ml of boiling sodium hydroxide solution (clause 2.2). Immediately connect the flask with the digestion apparatus (clause 1.2) and boil further for exactly 30 minutes. Remove the flask and immediately filter through Gooch crucible or alundum crucible (clause 1.4). Wash with hot water until it is free from alkali and then with 10 ml of alcohol (clause 2.5). Dry at 105-110 °C in an air oven for about 2 hours. Cool to room temperature in desiccator and weigh. Repeat the process of 30-minute drying, cooling and weighing until the difference between two successive weighings is less than 1 mg. Note the lowest weight which shall be considered as the weight of crucible and contents after drying.

Incinerate the contents and the crucible in the electric muffle furnace at 600+20 °C for about 30 minutes. Cool to room temperature in desiccator and weigh.

Repeat the process of 30-minute incinerating, cooling and weighing until the difference between two successive weighings in less than 1 mg. Note the lowest weight which shall be considered as the weight of crucible and ash after incinerating. The difference between the two weighings is the weight of crude fibre.

4 Calculation

Crude fibre, % by weight = 100(W₁-W₂)/W Where W is weight of sample, g

W1 is weight of crucible and contents after drying, g. W2 is weight of crucible and ash after incinerating, g 

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Keywords: laboratory method determination pulp fibre fiber starch