Effect of commercial hauling practices and tanker cleaning treatments on raw milk microbiological quality

Consolidation of the US milk industry has led to use of tankers for up to 24 h in between thorough cleanings. As the heavy use of tankers has not been previously studied, the effect of this form of hauling on raw milk quality is unknown. This study focused on the effect of frequent tanker use during hauling on raw milk quality at a commercial facility. Standard tanker use (cleaned-in-place once per 24 h) served as our control and incremental cleaning treatments (water rinse after each load, water rinse after each load with a sanitizer treatment after 12 h, and 12 h of sanitizer treatment) were added to the study to understand if any effect could be mitigated by more frequent cleaning. Producer samples were collected from the farm before loading milk into the tanker as well as sampling the same milk directly out of the tanker truck before unloading at the manufacturer. The study was repeated at 2 different dairy manufacturing facilities, once during the summer and once during the winter. Milk quality was quantified through industry-relevant microbiological tests: individual bacteria count, thermophilic spore count, and preliminary incubation count. Within the study we defined a negative effect on milk quality as a statistically significant difference between the tanker and producer samples in any of the 3 microbial tests conducted between treatments. Results from the study showed no clear effect due to hauling in individual bacteria count, thermophilic spore count, or preliminary incubation counts. There was also no difference in milk quality between the 2 plants, suggesting that neither season nor location affected our results in the standard use variable. As we did not see a negative effect on milk quality in the standard use variable, the addition of cleaning treatments did not appear to provide any clear benefit. Tanker surface swabs and ATP swabs were also used to monitor tanker sanitation and the efficacy of cleaning treatments. Both surface and ATP swabs revealed differences between cleaning efficacy at the 2 facilities. Although the differences in efficacy did not influence tanker milk quality within our study, variability in sanitation may provide a source of contamination that could negatively affect raw milk quality in other areas. Based on this study, current hauling practices appear to be effective in mitigating any measurable effect on raw milk quality; however, further investigation is needed before making industry-wide recommendations.