A simple oxygen sensor-based system for rapid testing of microbial contamination in raw meat samples and carcasses

Meat safety and quality are of utmost importance for the food industry, due to their implications in public health and welfare. The total aerobic microbial count (TAMC) is an important quantitative microbiological index used for evaluation of meat cuts and carcasses. Conventional methods of TAMC testing of meat samples (ISO4833-1:2013) and carcass swabs (ISO17604:2015) involve sampling followed by recovery of viable bacteria by homogenisation of the meat samples or the sponge swabs to obtain the initial suspension. Subsequent dilutions, plating onto agar media, incubation, and counting of the colonies on the plates are required to determine TAMC, giving testing time-to-result of 48-72 hours. We applied respirometry to develop an oxygen sensor-based method for testing TAMC in raw beef samples and carcass swabs. The method uses the same sample preparation procedure to obtain the initial suspension as the conventional tests, but we substituted plating and following steps with a sensor-based detection and quantification. We prepared disposable 25 mL vials with growth medium and built-in phosphorescent O sensor, to which sample homogenates were poured. Tubes are incubated on a block heater. A handheld optical reader FirestingGO2 was used to hourly read sensor signals to determine signal Threshold Time (TT) for sample vials. Calibration curves were generated to calculate the microbial load in unknown samples from measured TT values. The method showed good correlation with the standard ISO methods, with correlation coefficients 0.85 and 0.83, for meat and carcass samples respectively. The testing requires no dilutions, covers the ranges 2-7 Log(CFU/g) for the meat samples and 1-7 Log(CFU/cm) for carcass swabs, and has TT of 1-10 hours with faster detection of more contaminated samples. The testing system is rapid, simple, affordable, provides good sensitivity and analytical performance, and allows on-site use. It can be adopted by the meat industry and research labs, and used for microbial quality and safety assessment of meat products and processes.