Fibre introduction, extraction, estimation , principle, materials required, procedure, observation and calculation, result , references, note, formulas for calculating crude fibre.

3. Fiber - Introduction
o Crude fiber is a measure of the quantity of indigestible
cellulose, pentosans, lignin, and other components of this
type in present foods.
o It is the residue of plant materials remaining after
solvent extraction followed by digestion with dilute acid
and alkali.
o These components have little food value but provide the
bulk necessary for proper peristaltic action in the
intestinal tract.

4. Fiber - Introduction
o A determination of crude fiber is used in evaluation the efficiency of
milling and separating bran from the starchy endosperm.
o Crude fiber is also useful in the chemical determination of
succulence of fresh vegetables and fruits; over mature products have
increased levels of crude fiber.
o Today’s accepted term for fiber is dietary fiber, but this term has
only been in use since late 1970s. Before that, the primitive term
crude fiber was used because fiber was not considered important to
health.

5. Fiber - Introduction
o The non-digestible or dietary fiber fraction is a
complex mixture of different substance.
o The major ones are cellulose, the glucose polymer
that is predominant material of plant cells;
hemicellulose, a shorter version of cellulose: pectin,
the glue that binds plant cells together with cellulose
from the woody cell walls of plants.

6. Fiber - Introduction
o Fiber offers a variety of health benefits and is essential in reducing
the risk of chronic disease such as diabetes, obesity, cardiovascular
disease and diverticulitis.
o Dietary fiber acts to lower the concentration of low density
lipoprotein cholesterol in the blood, possibly by binding with bile
acids.
o The lignin fraction has been identified as the possible binding agent.
o It is a known fact that fiber helps eliminate waste from the
gastrointestinal tract because of its ability to bind water and thus
soften the stool.

7. Estimation of crude fiber
o Crude fiber consists largely of cellulose and lignin
(97%) plus some mineral matter.
o It represents only 60% to 80% of the cellulose and
4% to 6% of the lignin.
o The crude fiber content is commonly used as a
measure of the nutritive value of poultry and
livestock feeds and also in the analysis of various
foods and food products to detect adulteration,
quality and quantity.

8. Principle
o During the acid and subsequent alkali
treatment, oxidative hydrolytic degradation of
the native cellulose and considerable
degradation of lignin occur.
o The residue obtained after final filteration is
weighed, incinerated, cooled and weighed
again.
o The loss in weight gives the crude fiber

9. Materials
o Sulphuric acid solution (0.255 ±0.005N) : 1.25g
concentrated sulphuric acid diluted to 100mL
(concentration must be checked by titration)
o Sodium hydroxide solution (0.313 ±0.005N0 : 1.25g
sodium hydroxide in 100mL disyilled water
(concentration must be checed by titration with
standard acid)

10. Procedure
o Extract 2g of ground material with ether or petroleum ether to
remove fat (Initial boiling temperature 35 -38°C and final
temperature 52°C). if fat content is below 1%, extraction may be
omitted.
o After extraction with ether boil 2g of dried material with 200mL
of sulphuric acid for 30min with bumping chips.
o Filter through muslin and wash with boiling water until washing
are no longer acidic.
o Boil with 200mL of sodium hydroxide solution for 30min.

11. Procedure
o Filter through muslin cloth again and wash with 25mL of boiling
1.25% H2SO4, three 50mL portions of water and 25mL alcohol.
o Remove the residue and transfer to ashing dish (preweighed
dish W1).
o Dry the residue for 2h at 130 ±2°C.
o Cool the dish in a desiccator and weigh (W2).
o Ignite for 30min at 600 ±15°C.
o Cool in a desiccator and reweigh (W3).

12. Calculation
% crude fiber in ground sample =
Loss in weight on ignition (W2 - W1) – (W3 - W1)
______________________________________ ×100
Weight of the sample

13. Reading
o Maynard, A J (Ed) (1970) Methods in Food
Analysis Academic Press New York p 176.

14. Videolinks
o https://www.youtube.com/watch?v=D5iUzltVW
iI
o https://www.youtube.com/watch?v=p1a3kctJuI
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15. Thank you