Abstract #M156

# M156
Employee training and updated chemical sanitation may be insufficient for resolution of post-pasteurization contamination in HTST fluid milk plants.
Samuel J. Reichler*1, Sarah I. Murphy1, Tony Erickson2, Nicole H. Martin1, Kathryn J. Boor1, Martin Wiedmann1, 1Cornell University, Ithaca, NY, 2Ecolab Inc, Eagan, MN.

Among 280 samples of HTST pasteurized fluid milk collected from 10 dairy plants in the northeastern United States from 2015 to 2016, 132 (47%) showed evidence for spoilage due to post-pasteurization contamination (PPC) with gram-negative bacteria, some of which is known to survive normal cleaning and sanitation due to the formation of tough biofilms. PPC negatively affects the quality and shelf life of milk through the development of flavor, odor, texture, and visual defects. To address this high level of PPC, we examined the efficacy of 2 strategies aimed toward reducing the rate of PPC in fluid milk: (1) employee training both alone and (2) with concurrent implementation of updated sanitation protocols intended to remove persistent biofilm within equipment. Two large New York State fluid milk plants received employee training only, and 2 received both employee training and concurrent sanitation changes provided courtesy of Ecolab. Efficacy of the training was evaluated using surveys administered immediately before and after the training exercise, as well as approximately 8 mo after the training. Training and sanitation efficacy were evaluated through collection of finished product and subsequent refrigerated shelf life testing. Isolates collected from the milk over shelf life believed to represent PPC were collected and sequenced to provide identification and subtyping for determination of recurrent isolation. Though plant employees generally indicated that the training altered their perceptions of the causes of PPC, no significant changes in the occurrence of PPC were observed associated with either the training alone or with the training combined with changes in sanitation. Furthermore, multilocus sequence typing revealed a general lack of persistence in bacterial strains responsible for PPC at a given plant over the course of weeks and months. These results suggest that a more holistic and intensive approach may be necessary to reduce the occurrence of PPC in dairy plants, such as redesign or replacement of equipment that cannot be effectively cleaned and sanitized, or workplace modifications to enforce desired employee behaviors.

Key Words: post-pasteurization contamination, sanitation, training