Suitability of ATP Bioluminescence Compared to pH Measurement or Microbial Growth on Agar to Evaluate Commercial Sterility in UHT Milk

Introduction: Rapid technologies, such as microbial-ATP detection have focused on detecting microbial contamination in shorter times than traditional methods, allowing a faster time to release of Ultra-High Temperature (UHT) processed products. The use of ATP bioluminescence is a rapid alternative method. Argentina regulations require pH measurement of UHT milk after seven days of incubation at 35°C for product release. Some bacteria may not reduce pH after seven days of incubation and may hamper the microbial quality of this type of product.

Purpose: This study evaluated the reliability of using an ATP bioluminescence method and pH measurement to screen for commercial sterility.

Methods: ATP bioluminescence, pH and agar methods were used to evaluate 120 samples. Three different products (n=40/product) were tested; whole, low fat and chocolate milk. A set of 60 samples was incubated for 48h at 35°C and an additional 60 samples at 72h at 35°C for enrichment. Forty-five samples were spiked with ≤10 CFU Pseudomonas aeruginosa and 45 with ≤10 Bacillus cereus. Positive controls were spiked with 100 CFU and 30 samples were not spiked.

Results:  Samples spiked with Pseudomonas did not present a pH decline, however it was detected by growth on agar and ATP bioluminescence. Samples spiked with Bacillus showed a limited pH decline after 48h and was, also, detected by growth on agar and ATP bioluminescence. Microbial contamination was not determined in uninoculated samples evaluated with any of the three methods.

Significance: Bioluminescence technology provides a rapid alternative for evaluating commercial sterility in UHT milk and has offers UHT manufacturers a reliable alternative for product release with equivalent results to determination of microbial growth on agar and with better reliability than pH measurement.