ATP-bioluminescence assay as an alternative for hygiene-monitoring procedures of stainless steel milk contact surfaces

ATP-bioluminescence assay was used to evaluate the cleaning and sanitizing procedures of stainless steel milk contact surfaces. Surfaces of a raw milk transportation tank, a raw milk cooling storage tank, an equalization pasteurizing tank, a pasteurized milk storage tank and a pasteurized milk packaging tank, as well as a milk centrifuge were evaluated. The Relative Light Unit (RLU) using a commercial luminometer and mesophilic aerobic counts (CFU.cm(-2)) on surfaces were determined. There were no significant differences (p > 0.05) in RLU on the assessed surfaces before and after the cleaning and sanitizing procedures. Also, there were no significant differences (p > 0.05) in CFU.cm(-2) on the surfaces before the cleaning and sanitizing procedures, whereas different bacterial numbers were found on surfaces after the hygiene procedures. The surfaces of the milk centrifuge, raw milk cooling tank and milk packaging tank showed the largest mesophilic aerobic numbers after the hygiene, reaching 2.21, 2.18, and 1.21 log(10), respectively. The results demonstrated that there is no agreement among the techniques for classification of hygienic conditions of the evaluated surfaces, showing a non-direct relation between RLU and CFU.cm(-2). The ATP-bioluminescence method showed that 100% of the surfaces were under inadequate hygiene conditions, while the plate count method detected only 50%, based on the APHA's recommendation, and 33%, based on the WHO's recommendation. High variations in RLU measurements were observed, suggesting the need for more than only one surface analysis. The ATP-bioluminescence is not a direct replacement for microbiological testing, but provides complementary information and should be used as part of an integrated strategy.