KOH Protein Solubility
Described by: Araba M. and N. M. Dale. 1990. Evaluation of protein solubility as an indicator of overprocessing of soybean meal. Poultry Science 69:76-83.
Whittle, E. and M. Araba, 1992. Sources of variability in the protein solubility assay for soybean meal. J. Appl. Poultry Res. 1:221-225.
Place approximately 1.5 g of sample in a 250 mL beaker. Important: sample should be finely ground - # 60 mesh
Add 75 mL of 0.2% KOH solution.
Stir mixture for 20 minutes at 22o C at 75% of maximum velocity using Corning Model PC-351 stir plate with a magnetic stir bar 3.6 cm in length.
At end of 20 minutes, approximately 50 mL of liquid is collected into centrifuge tubes.
Centrifuge (Beckman Model GPR) at 1250 x g for 10 minutes.
Collect a 15 mL aliquot of the supernatant.
Perform macro Kjeldahl procedure on 15 mL aliquot (mg N/mL setting; input 15 as the sample size) and original sample (percent protein setting) to determine crude protein level.
Calculate protein solubility as percentage of total in the original sample.
KOH Solution Recipe (weight/volume)
0.2% KOH = 0.2 g of KOH in 100 mL deionized distilled water. Mix in hood.
0.5% KOH = 0.5 g of KOH in 100 mL deionized distilled water. Mix in hood.
Sample weight - 1.5072 g
Liquid Kjeldahl value - 1.125 mg N/mL
Dry Kjeldahl value - 47.47% protein
1.125 mg N x 75 (how much KOH added) = 84.4 mg N = 55.98 mg
N = 5.598 g N
mL 1.5072 g mL 100 g sample
5.598 g N x 6.25 = 34.99% CP
(34.99/47.47) x 100 = 73.68% solubility