Precision of the Pro-Milk Method in Routine Determination of Protein in Dairy Testing Laboratories ¹

Area of Science:

• Dairy Science
• Analytical Chemistry
• Food Analysis

Background:

• Accurate protein determination in milk is crucial for quality control and commercial value.
• The Pro-Milk Mark II dye-binding method offers a rapid alternative to traditional methods like Kjeldahl.

Purpose of the Study:

• To evaluate the repeatability and reproducibility of the Pro-Milk Mark II method for milk protein analysis.
• To identify factors influencing the method's performance and suggest improvements.

Main Methods:

• A collaborative study involving multiple laboratories was conducted.
• The Pro-Milk Mark II dye-binding method was assessed for protein determination in milk.
• Results were compared against the Kjeldahl method for calibration accuracy.

Main Results:

• Repeatability (r) was 0.053% protein and reproducibility (R) was 0.215% protein at 95% confidence.
• Factors affecting repeatability included sampling, reading errors, and equipment performance.
• Reproducibility was also impacted by calibration accuracy against the Kjeldahl reference method.

Conclusions:

• The Pro-Milk Mark II method demonstrates acceptable precision for milk protein analysis.
• Centralizing laboratory calibration and calibrating equipment across a broad protein range are recommended.
• These measures will enhance the accuracy and reliability of protein content determination.