Determination of fat in raw and processed milks by the Gerber method: collaborative study

Area of Science:

• Dairy Science
• Analytical Chemistry
• Food Analysis

Background:

• The Gerber method is a globally recognized, rapid technique for quantifying fat content in milk.
• International standardization of the test portion volume for the Gerber method is lacking.
• This study addresses the variability in test portion measurement for the Gerber method.

Purpose of the Study:

• To evaluate the performance of the Gerber method using a weighed test portion (11.13 g) versus a pipetted volume (10.77 mL).
• To compare the accuracy and precision of both Gerber method variations against the Mojonnier ether extraction reference method.
• To determine the optimal application of the Gerber method based on test portion measurement and milk fat content.

Main Methods:

• A collaborative study involving 11 and 10 laboratories for weighed and pipetted methods, respectively.
• Analysis of 10 milk samples (5 raw, 5 pasteurized) with varying fat content (0.96-5.48%).
• Comparison of results with Mojonnier ether extraction (AOAC Method 989.05) as the reference standard.

Main Results:

• Interlaboratory study statistics were comparable between weighed and pipetted test portions and across raw and processed milks.
• Pooled statistical performance: repeatability (sr) = 0.026, reproducibility (sR) = 0.047.
• The pipetted method showed significantly lower fat results (0.06% fat) compared to ether extraction, while the weighed method was slightly lower (0.02% fat).

Conclusions:

• The Gerber method demonstrates consistent performance regardless of test portion measurement method (weighed or pipetted).
• A trend of underestimation was observed with the weighed portion at lower fat concentrations (1-2%), but not with the pipetted portion.
• Recommendation for adoption of the Gerber method with a weighed test portion as First Action for whole milk analysis.