EFFECT OF MILK SAMPLE CONDITION ON REPLICATE MILKFAT TESTS ANALYZED BY A MILKO-TESTER MK II

Abstract

Milk sample variables of homogeneity, age, temperature, pH, and fat level, as well as the fat level used to standardize the Milko-Tester MK II were studied in relation to repeatability of results. Fresh milk samples from individual cows as well as from a bulk tank of low (3.2%) and high (5.0%) fat levels were used for these studies. Milk was warmed to 38 C and subdivided into twenty 120-ml portions and placed in plastic sample bags before analysis. Half of the samples in addition to the normal mixing received mild agitation by hand-squeezing the bags during pipetting. The difference between the means of agitated, hand-squeezed, and non-agitated, not squeezed, samples was only +0.009%. The average deviations from the Babcock standards showed that when the Milko-Tester was standardized with low fat milk, the low fat samples deviated by +0.003% while the high fat samples deviated by +0.076%; with high fat standardization, the high fat samples deviated by −0.002% while low fat samples devioted by −0.058%. Temperatures of pipetting in Milko-Tester at 21, 31, and 39 C had no great effect on the difference between samples. Analysis by the Milko-Tester of samples preserved with potassium dichromate as well as non-preserved samples stored at 9 C and 21 C for 1–22 days showed a decrease in fat test when the pH decreased to 6.50.