Principle
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Acid detergent fiber is determined as the residue remaining after adding an acidified solution. It is the NDF without the hemicelluloses. Cell soluble, hemicelluloses and soluble minerals dissolve. Cetyl trimethyl-ammonium bromide (CTAB) separates proteins from the remaining cellulose and lignin, and minerals (ash). The acid detergents solution recovers cellulose and lignin.
ADF determination is a preparation step for lignin determination.
Procedure
• Add 0.5–1 g sample (Ws) in 600 ml Berzelius beaker
• Add 100 ml of acid detergent
solution
• Boil for one hour on refluxing
Equipment
• Precision balance (Fig. 5)
• Refluxing apparatus (Fig. 15)
• Vacuum filtering system with trap in line (Fig. 16)
• Desiccator (Fig. 7)
• Berzelius beakers (600 ml)
• Sintered glass crucibles (coarse porosity 1) (Fig. 17).
apparatus
Figure 16. Vacuum filtering system with
trap in line
Figure 17. Glass crucible, porosity 114
• Weigh oven–dry glass crucible (Wt)
• Pour through glass crucibles
• Admit vacuum
• Rinse crucibles with approximately 50 ml hot water four times until
all traces are removed
• Rinse with acetone repeatedly until drained liquid is cleared
• Dry at 105 °C overnight
• Cool to room temperature in desiccator
• Weight sample and crucible (W0)
• Ash residues for three hours at 550 °C
• Cool to room temperature in desiccator
• Weight crucibles and residues (Wa).
Calculations
%ADF = [(W0–Wt)/Ws]×100
ADF expressed as organic matter:
%ADFash = [(Wa–Wt)/(W0–Wt)]×100
Acid detergent solution
• 20 g cetyl trimethylammonium bromide (CTAB)
• 1l of 1.0 N sulfuric acid (H2SO4).
References
• Goering HK and VanSoest PJ. 1970.
• AOAC. 1995.
• Undersander D, Mertens DR and Thiex N. 1993.
