Determining the microbial quality of pasteurized milk through the ATP-bioluminescence method

Microbiological control of pasteurized milk quality is an important step before it consumed. Current standard methods for determination of pasteurized milk microbial quality are culture based, which are laborious and time-consuming, where results not are available before one to three days after sampling. ATP bioluminescence technique is a new technology in determining the quality of pasteurized milk. This study presents the quality control of pasteurized milk by ATP bioluminescence method, correlation with cultural methods and finally biochemical and molecular identification of selected microorganisms. Pasteurized milk samples were collected from local markets in Manisa province at certain time intervals and obtained in appropriate amounts and taken to microbiological analysis by cultural methods. As a result of microbiological counts, total aerobic microorganism was found below 105 cfu/mL pasteurized milk spoilage limit. Enterobacteriaceae was determined in 34% (n=17) of the samples tested and was below 104 cfu/mL, all milk samples were negative for coliform. The presence of aerobic bacterial spore was detected in 33 (66%) samples; the lowest and highest values were calculated as 1.0 x 101 and 7.6 x 102 cfu/mL, respectively. The thermoduric microorganism was determined in only 2 (4%) samples with a maximum of 2.0 x 102 cfu/mL. The total number of aerobic microorganisms, as a result of the cultivation on Petrifilm ready culture media, showed average values ranging from 1.0 x 101 to 1.1 x 103 cfu/mL. Enterobacteriaceae was found to be below the counting limit as 1.2 x 102 cfu/mL in 34 of 2 (6%) samples. However, typical E. coli was detected in 1 (3%) of the samples. Yeast/mold was not detected for none of the milk samples. The measured values of 50 different pasteurized milk samples analyzed by ATP bioluminescence technique ranged from 46-9858 RLU. When we compared the measured values of ATP bioluminescence with our standard values, it was concluded that 4 (8%) of the 50 pasteurized milk samples were analyzed bad quality, 5 (10%) were suspicious and the rest were good quality (82%). However, between colony counts obtained with petrifilm cultures or different selective media and ATP bioluminescence measurement values of pasteurized milk were found to be weak correlation. 11 selected different bacteria as a result of isolation by cultural methods are identified by morphological, cultural characteristics, biochemical tests and 16S rRNA sequence data. The identified species are Acinetobacter lwoffii, Acinetobacter johnsonii (2 isolates), Acinetobacter junii (2 isolates), Escherichia coli, Aeromonas media (2 isolates) and Aeromonas hydrophila, respectively. In addition, 2 bacteria on the genus level were identified as Escherichia sp. and Acinetobacter sp. These bacterial species isolated and identified from pasteurized milk samples are opportunistic pathogens. It is concluded that the quality of 8 (16%) pasteurized milk is not in accordance with the standards by collectively evaluating the cultural studies and ATP method findings and ultimately identifying opportunistic pathogens. According to the research findings, it is possible to determine the microbial load of pasteurized milk by ATP bioluminescence method but it is necessary to conduct cultural and advanced tests for the detection of pathogens.