Purpose: The objective of this study was to evaluate a new application of 3M™ Microbial Luminescence System (MLSII) with soy-based UHT products, including those with neutral (7.0-7.2) and low (3.8-4.0) pH.
Methods: 480 samples of soy-based products, including neutral and acidic ones, were artificially contaminated with very low levels of microorganisms (< 1 CFU/ml). 4 microorganism groups were used – Enterobacteriaceae (E.coli), Bacillus (B.coagulans, B.stearothermophyllus, B.subtilis), Lactobacillus (L.plantarum, L.casei) and Yeasts (Picchia anómala, Saccharomyces cerevisiae). Contaminated samples were incubated 48 and 72 hours at 32-35 °C and analyzed in duplicate by standard plate count method and the new method to detect microbiological growth. Six hundred samples from both product categories were tested to establish background levels of product ATP.
Results: Results show that reagents used for bioluminescence detection were capable of reducing the product ATP of samples to average levels of 10-20 RLU. Bacteria on artificially-contaminated neutral samples were detected after 48 hours of incubation and for acid samples the detection was at 72 hours for E.coli. However, acid samples contaminated with Bacillus didn’t develop any growth when incubated up to 10 days. Samples contaminated with yeasts were detected after 72 hours for both types of products. All results obtained with the new method corresponded with positive samples in standard plate count method.
Significance: The new method is a reliable alternative for detecting microbiological contamination in aseptic non-dairy products. Bioluminescence system allows quicker and reliable results compared to traditional microbiological methods and pH testing as some contaminated samples didn’t present any significant pH variation.