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Chemistry Of Crude Fibre

Crude fibre refers to the residue of a feed that is insoluble after successive,boiling with dilute acid and alkali. This method was originally proposed at the weende experiment station. Hence this method on determination of crude fibre is known as Weende s method of determination of crude fibre.

Crude fibre is the portion of the total carbohydrate of a food that is resistant to the acid and alkali treatment.

The Weende scheme of proximate analysis  is to separate the total carbohydrate into two categories viz. crude fibre and Nitrogen free extractives. Nitrogen free extractives represents the soluble sugar starches,glycogen,some fraction of hemicellulose and of course other water soluble components like water soluble vitamins etc.

As per Weende method, crude fibre is the fraction of carbohydrate that remains after treatment with acid and alkali.

Effect of acid and alkali treatment on a fat free food





1.25% H2 SO 4

1.25 % NaOH


Partial extraction

Complete extraction

Starches and sugars

Hydrolysis and extraction



variable extraction

Extensive but variable extraction


variable extraction

Extensive but variable extraction

Lignin extraction


Extensive but highly

But this method any insoluble material after the acid and alkali digestion will be made up of (1)all original cellulose (2) variable proportion of hemicellulose (3) a small but highly variable portion of lignin.