Evaluation of the Babcock Method for the Determination of Milk Fat

Abstract

Abstract The Babcock test for fat in milk was evaluated to study the effects of variables such as glassware calibration, sample preparation, sample composition, reagents, tempering conditions, procedural variations, and analyst. Certain test bottles yielded significantly different results; however, there was little indication of pipet variation. Analysis of the various techniques for tempering and mixing indicated that samples tempered at 68°F (20°C), containing an airspace of approximately 25% of the total container, and mixed by inversion 5–10 times or poured from one container to another gave the most consistent results. Sample composition did not affect results, provided all milk-solids-notfat were digested by the sulfuric acid. A pipet draining time of 10 sec followed by blowing out the pipet was sufficient to yield reproducible results. Differences between lots of sulfuric acid affected results. Results were 0.027% less when the final test tempering was 130°F (54.5°C) compared to 140°F (60°C); however, a final tempering for a minimum of 3 min gave satisfactory results. Variations in reading results between individual analysts were negligible. The Babcock method for fat in milk, modified to include the optimum parameters as determined in this study, was subjected to a collaborative study. Nine laboratories analyzed 10 samples in duplicate. Statistical analysis of collaborative data indicates a significant difference between laboratories (p <0.01 ). The repeatability standard deviation of the method is 0.0183%. The reproducibility standard deviation is 0.0407%. The repeatability and reproducibility coefficients of variation are 0.53 and 1.17%, respectively. On the basis of the collaborative results, the following changes have been incorporated into the official final action method: specifications for the reading light; sample draining time; tempering temperature of the acid; tempering procedure for reading the test bottle.