Protein in Raw / Homogenized Milk

UDY Dye Method


An acidic solution of monosulfonic azo dye, Acid Orange 12, reacts with basic groups on protein to form an insoluble complex. The protein=s dye binding capacity (DBC) is genetically controlled and is essentially constant for any given protein system. The estimate of protein content is based on colorimetric measurement of unbound dye. The dye serves as a primary standard.


Applicable to raw or UDY-Pol preserved milk from all dairy breeds as well as to modified milk such as homogenized, pasteurized, skim, etc.

Apparatus and Reagents

UDY Model MKP Protein Analyzer including an UDY Dairy Tester (Colorimeter) along with Standard Reagent and Reference Dye Solutions.

Initial Set-Up

  1. Drain Bottle and Tubing - Attach the end of the Drain Tube (feed tubing up through the bottom of the unit) to the Cuvet Tip. It may be necessary to moisten the tip of the Cuvet with water to make the attachment easier. Wipe off any fingerprints on the Cuvet with a soft tissue or a soft cloth.
  2. After the tubing is attached, seat the Cuvet Stop making sure that the scribe mark on the top of the Cuvet faces the front.
  3. Connect the Power Supply to the unit and plug the Power Supply transformer into the appropriate outlet. Make sure the unit switch is in the OFF position before plugging in the unt.
  4. Turn on and warm up the unit for 30 minutes before operating.
  5. Follow the operating instructions below.

Protein Test Set-Up

  1. Fill the Cuvet with demineralized water. Start the flow-through process by gently squeezing the Drain Bottle. Place your finger over the vent hole of the Drain Bottle Cap and release.
  2. Place Colorimeter switch to CAL position.
  3. Adjust ZERO Potentiometer to read .000 on meter.
  4. Fill the Cuvet with A66" Standard Reference Dye Solution.
  5. Adjust GAIN Potentiometer to read .660 on the meter.
  6. Place the Colorimeter switch to %Protein position.
  7. Place SET switch on appropriate channel No.1, 2,3,or 4 for raw or homogenized milk. (See Factory Set Up Sheet).
  8. Filter *sample (25-30 drops or until stable) into Cuvet and read %Protein (See Sample Prep).

*Sample/dye solution@ 25C

Sample Prep. - Raw/Homogenized Milk, etc.

  1. Warm milk sample to 37C and mix.
  2. Weigh out 2.06 g (2.0 ml) of milk into a tared 60 ml polyethylene Sample Bottle.
  3. Dispense40.37 g (40 ml) Reagent Dye Solution into the Sample Bottle. Cap the Sample Bottle and shake at least 15 - 20 seconds.
  4. Adjust the temperature of the solution to 25C.
  5. Add the Filter Cap Assembly to the Sample Bottle. Filter 25-30 drops into the cuvet.