VAN SOEST (DETERGENT FIBER)
The technique of using detergents to separate digestible and indigestible parts of plant tissues was initially proposed by Van Soest in 1963. The concept behind the detergent fiber analysis is that plant cell substances can be divided into less digestible cell walls (made of hemicellulose, cellulose and lignin) and highly digestible cell contents (containing starch and sugars). These two components are successfully separated by using different detergent systems.
>> NEUTRAL DETERGENT FIBER (NDF): the sample is digested in the Neutral Detergent Solution to separate the neutral detergent soluble fraction from the neutral detergent-insoluble fraction. The remaining dry matter is estimated and the proportion gives the neutral detergent fiber (NDF).
- DIGESTION: the sample is boiled in the Neutral Detergent Solution NDS with a heat-stable a-amylase-treated enzyme to separate the neutral detergent soluble fraction (sugars, starches and pectins soluble, filtered) from the neutral detergent-insoluble fraction (cell walls substances, hemicellulose, cellulose and lignin, residues)
- WASHING: the residues inside crucibles are washed with water to remove detergent residues
- DEFATTING: it is the final step, where the last washes are performed with acetone
>> ACID DETERGENT FIBER (AFD): the Acid Detergent Solution (ADS) solubilizes the hemicellulose while lignin and cellulose remain insoluble. The residue is weighed for the determination of ADF. It includes cellulose and lignin.
- DIGESTION: the Acid Detergent Solution (ADS) solubilizes the hemicellulose while lignin and cellulose remain insoluble in the crucible
- WASHING: the residues inside the crucibles are washed with water to remove detergent residues
- DEFATTING: it is the final step, where the last washes are performed with acetone
>> ACID DETERGENT LIGNIN (AFL): in sequential analysis, the remaining residues from ADF are solubilized by adding sulfuric acid 72 %. Only lignin and acid-insoluble ash remain after this step. The residue is then combusted in a furnace, and the difference in the weights before and after ashing yields the amount of lignin present in the sample.