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Soluble Protein

Reagents

  1. DEIONIZED WATER
  2. SODIUM PHOSPHATE, MONOBASIC, MONOHYDRATE (NaH2PO4.H20)
  3. SODIUM TETRA BORATE, DECAHYDRATE (Na2B407.10 H20)
  4. SODIUM BICARBONATE

Solution Preparation

BUFFER SOLUTION - Carefully weigh exactly 89.10 g of Sodium Tetra Borate, Decahydrate into a 250 mL beaker. Next, carefully weigh exactly 122.0 g Sodium Phosphate mono-basic, mono-hydrate into a 250 mL beaker. To a 4 L beaker, add approximately 3500 mLs deionized water and a stir bar (Large > 1"). With stir bar rotating slowly, carefully add Sodium Tetra Borate, Decahydrate. Use a squirt bottle containing deionized water to thoroughly rinse the weigh boat. Next, add the Sodium Phosphate monobasic, monohydrate. Again, use squirt bottle to thoroughly rinse weigh boat. Allow to stir until all crystals are dissolved.

IMPORTANT: DO NOT TURN STIRRER TOO HIGH AND CAUSE EXCESSIVE SPLASHING! After all crystals are dissolved, with a clean, dry stir bar retriever, remove stir bar from beaker. Rinse retriever and stir bar into beaker as bar is removed. DO NOT EXCEED THE 4000 mL VOLUME LINE DURING THIS RINSE. Bring beaker to 4000 mL mark. Transfer beaker contents into 20 L buffer carboy. Continue by adding 6000 mLs of deionized water to the 20 L carboy. This addition of deionized water is used to thoroughly rinse the beaker and bring the solution to the proper volume of 10 L (concentration). Mix the contents of the carboy. Before using, measure the pH of the solution. The normal range is 6.70-6.75.

To adjust pH up- use Sodium Bicarbonate.

To adjust pH down - use Hydrochloric Acid.

Procedure

  1. Weigh 0.5 g of sample into a clean, dry 250 mL Erlenmeyer Flask. Label flask with sample number.
  2. Add 50 mL of Borate-Phosphate buffer to each flask.
  3. Place caps on flasks, swirl gently and let stand 1 h.
    1. IMPORTANT NOTE 3: Soy Products (461,462,463,703,704,764) must be incubated in a water bath at 39oC for 1 h.
  4. After 1 h, samples are ready to filter. Filter samples through filter paper and air dry overnight.
  5. Analyze filter paper and residue for crude protein according to ADFN procedure (page 23). This is insoluble protein.
  6. Record values with 2 decimals.

Calculation

  1. Soluble Protein % = (Sample CP% - Residue CP%) x 100/Sample CP%

References

  1. NYDHIA
    Cornell Nutrition Conference proceedings (10/23/92).