DAIRY PRODUCT QUALITY - A NEW VISION FOR THE TWENTY FIRST CENTURY
Martin, Nicole Helen
The quality of dairy products relies on the implementation of best practices from the pre-harvest environment throughout the processing and distribution chain, requiring a grass-to-glass approach. The dairy industry has long used a number of parameters to determine the quality of dairy products, both at the farm level and the processing level. Milk quality at the farm has historically focused on somatic cell counts (SCC), which are indicators of udder health, while processors primarily focus on testing finished product for coliforms as indicators of hygienic processing conditions. The dairy industry has managed and tested for these parameters for decades, basing quality premiums and performance targets on them, developing rapid testing methods and investing in control strategies. While SCC and coliforms are indeed measures of raw and pasteurized product quality, respectively, research on contemporary dairy products reveals that these measures may not be adequately assessing the major influencers of dairy product quality and shelf-life, specifically in fluid milk. In fact, there are two primary causative groups of bacterial contaminants that lead to product spoilage in high-temperature, short-time (HTST) processed fluid milk in the United States, namely psychrotolerant sporeforming bacteria and Gram-negative bacteria. Psychrotolerant sporeforming bacteria enter the fluid milk continuum at the farm where they are ubiquitous in the environment. These organisms survive pasteurization in spore form and subsequently germinate and grow, reaching the Pasteurized Milk Ordinance (PMO) bacterial limit of 20,000 CFU/mL approximately 14-17 days after pasteurization. Studies have implicated sporeforming bacteria as the causative agent in approximately 50% of fluid milk reaching the PMO limit. In contrast, Gram-negative bacteria are eliminated by HTST pasteurization so their presence in finished product indicates that there has been re-contamination after pasteurization, also known as post-pasteurization contamination (PPC). Gram-negative bacterial contaminants, primarily Pseudomonas, grow rapidly at refrigeration temperatures, reaching the PMO limit 7-10 days after pasteurization. Our research indicates that approximately 50% of fluid milk reaches the PMO limit due to these Gram-negative bacterial contaminants. Importantly, coliforms, the traditional indicator organism in Grade “A” fluid milk are also a group of Gram-negative bacteria, but our work suggests that they account for a minor proportion of the total causative agents of PPC. Driving quality improvements in the dairy industry will require a new approach to defining quality parameters and addressing factors that influence those parameters in contemporary dairy products.
Food science; Coliforms; Dairy Quality; Post Pasteurization Contamination; Spoilage; Sporeforming Bacteria
Worobo, Randy W.; Giordano, Julio O.
Food Science and Technology
Ph. D., Food Science and Technology
Doctor of Philosophy
Attribution 4.0 International
dissertation or thesis
Except where otherwise noted, this item's license is described as Attribution 4.0 International