Characterization of Milk Hauling Practices and Their Impact on Raw Milk Microbiological Quality Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/ww72bh111

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  • The dairy industry has indicated that milk hauling sporadically compromises milk quality, but often the reason is unknown. Milk hauling practices are an underexplored area of research, and are in need of attention because during hauling milk is most exposed to the external environment in comparison with any other step of modern dairy processing. Milk hauling is defined as the activities associated with the transfer of raw milk from producer to tanker truck, which is then transported and unloaded into storage silos at a processing facility. Tanker are often used to haul several loads within a 24-h period without cleaning and sanitizing in between; a practice that is mandated by the Grade “A” Pasteurized Milk Ordinance (PMO). Repeated tanker usage between cleans is necessary in the modern dairy industry; less cleaning reduces chemical and water usage, and time. There is no specification on maximum loads hauled or idle time (empty and dirty) between loads. Additionally, many routine practices outlined in the PMO use vague wording (as needed) to describe frequency; this is to provide flexibility to industry since each facility is unique. However, this vagueness does not inform industry on what best practices entail; potentially leading to unexplained sources of contamination due to weaknesses in practices. The overarching hypothesis of our research is that milk hauling sanitation and operation practices have the potential to negatively contribute to the microbiological quality of raw milk and impact finished product quality. In the scope of our study, negative impact from hauling is defined as an increase in microbiological counts or microflora proteolytic and lipolytic enzyme activity. The aim of our research was to explore a vast range of hauling situations to see if they had potential to compromise raw milk quality; this was achieved by i) characterizing variability in industry hauling sanitation and operational practices, ii) identifying circumstances in which hauling contributes to a degradation in the microbiological quality of raw milk by analyzing two years of historic raw milk microbiological data from producers and tanker trucks of a Northwest co-op. and iii) investigating impact of worst-case hauling conditions (e.g. extended idle time between loads) by measuring raw milk microbiological counts and enzyme activity for two scenarios: a) a small-scale using stainless steel milk cans, b) commercial study using tanker trucks and a pre-selected route.As anticipated, variability in industry practices exists, especially for equipment that required manual cleaning, and preventative maintenance programs such as replacement of aged equipment and parts. Analysis of historic raw milk microbial counts indicated that microbiological counts were not likely to be influenced by hauling, but rather are influenced by on-farm milk quality. Low counts from the on-farm bulk tank will be maintained if best sanitation and operating practices implemented at every step of the process, including milk hauling. Our small-scale milk can study demonstrated that extended idle time (> 6 hours) between loads has potential to negatively impacts milk quality, and provided a proof-of-concept for scaling up to a commercial study. Negative impact on milk quality was demonstrated to not be measurable for commercial tankers remaining dirty and idle for periods of <6 h between loads. Current PMO regulations (clean per 24 hours) appears to be adequate as long best sanitation and operation practices are implement. Future advances in rapid microbiological testing may facilitate better methods for measuring raw milk quality, especially as we better understand influences of raw milk microflora on downstream quality of dairy products.
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