Master of Science (MS)
Animal Science (Animal, Dairy, and Poultry Sciences)
The objectives of this study were to provide an overview of fluid milk quality in the U.S., determine if there is a correlation between rapid and traditional tests, determine if results from different analyses correlate with a sensory analysis and to determine any correlation between any of the analyses done in this study. Whole and 2% milks were received from 17 dairy processing plants located in the west, midwest, and southern regions of the U.S in duplicates. Samples were pasteurized at the processing plants by HTST method (161-175oF for 15-25 seconds). For standard plate counts at day 0 no significant differences were found. The mean value was 1.89 log CFU/ml. In day 14, significant differences were found. The mean was 7.58 log CFU/ml. No coliforms were found in any of the samples on either day 0 or day 14. Psychrotrophic counts had no significant differences for the traditional method. 5% of the samples showed psychrotrophic counts. For the rapid method no significant differences were found. The mean value was 0.63 log CFU/ml. 10% of the samples showed psychrotrophic counts. For heat-resistant spore-forming psychrotrophs no significant differences were found. 10% of the samples showed psychrotrophs. For aerobic spores no significant differences were found. The mean value was 1.94 log CFU/ml. HR-1 tests showed no significant differences. The mean was a pink coloration. HR-2 test results did result in significant differences at 48 and 60 hrs, with a mean of a pink color. HR-3 tests showed a mean of pink. Significant differences were found among samples. Fat% results had no significant difference for either milk samples. 2% samples had a mean of 2.08%. Whole milk samples had a mean of 3.43%. Protein content showed no significant differences. The mean was 3.15%. No significant differences were found for somatic cell counts. The mean value was 1.77 log SCC/ml. Regarding sensory evaluation, for day 0 no significant differences were found. The mean score was 7. Day 14 showed significant differences with a mean score of 4.39. Both test methods of psychrotrophic counts shared a high correlation coefficient but a t-test confirmed otherwise. We can conclude that the fluid milk quality in the U.S. needs to be improved.
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Vargas, Jose Luis, "Determinants of fluid milk quality" (2009). LSU Master's Theses. 4004.
Charles A. Boeneke