Determination of Acid Detergent Fiber (ADF)

Principle

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.