Method/principle of analysis
After any necessary grinding and de-fatting, boiling with sulphuric acid solution of standard concentration, and filtration and washing of the insoluble residue. Boiling this residue with sodium hydroxide (or potassium hydroxide) of standard concentration, then filtration, washing, drying and weighing of the insoluble residue, and determination of the loss in mass on incineration.
Neutral detergent solution and heat-stable alpha-amylase are used to dissolve the easily digestible proteins, lipids, sugars, starches and pectins in feeds, leaving an insoluble fibrous residue that is primarily cell wall components of plant materials (cellulose, hemicelluloses and lignin) and indigestible nitrogenous matter in animal products.
Cationic detergent solution is used to remove acid-labile carbohydrates, protein that is not complexed into Maillard products (heat damaged) and fats. The remaining fibrous residue is primarily cellulose and lignin (plant products) or insoluble protein complexes (animal products and heat-damaged feeds). The residue is weighed for the determination of ADF.
After ADF, the remaining residue is solubilized by 72 % mass fraction (12.00mol/l) sulphuric acid, leaving the lignin (ADL) which is determined gravimetrically.