Evaluation of adenosine triphosphate-bioluminescence hygiene monitoring for trouble-shooting fluid milk shelf-life problems.

An ATP-bioluminescence hygiene monitoring system was used to evaluate food contact surfaces in four fluid milk plants experiencing shelf-life problems. Postpasteurization surfaces, including gaskets, pipe fittings, valves, filler parts, and hand-washed items, were evaluated. Swab results, measured in relative light units proportional to total recovered ATP, were compared with results from the standard method of microbiological swab contact for adjacent sites of equal area. Microbiological procedures included standard plate count, coliform count, and Gram-negative bacteria count. Standard plate counts were < 1, 1 to 50, and > 50 cfu in 65, 22, and 13% of swabbed sites of < 100 RLU (relative light units); in 9, 36, and 55% of sites of 100 to 150 RLU; and in 22, 18, and 60% of sites of > 50 RLU, respectively. Thirteen sites were found with standard plate counts > 10,000 cfu per site and identified with the hygiene monitoring system (> 150 RLU). Gram-negative bacteria were the dominant bacterial type in a majority of these samples. Gram-negative bacteria were detected in a total of 22 sites tested; mean counts were 2100 cfu per site for Gram-negative bacteria and 20 cfu per site for coliform bacteria. Although limited to use on accessible sites, the hygiene monitoring system proved to be an effective, rapid tool for identifying the possible sources of postpasteurization contamination in the fluid milk plants evaluated.