Microcalorimetry as a Rapid Method for Estimation of Bacterial Levels in Ground Meat

The potential of microcalorimetry as a rapid method for the estimation of bacterial levels in ground meat was studied. The exothermic heat production rates (HPRs) of Escherichia coli and meat suspensions were measured in a BioActivity Monitor and correlated to log₁₀ CFU/ml or g. Comparative experiments using 0.1% peptone saline (PS) or nutrient broth (NB) as the suspending medium showed that maximum HPRs (peak times) were obtained faster with NB than with PS, and that HPR peaks were more distinct when using NB. Two series of 11 meat samples suspended 1:10 in NB were examined at instrument operating temperatures of 21 and 30°C, respectively, and HPRs were compared to mesophilic colony counts (30°C/3 d) and to psychrotrophic counts (17°C/17 h then 7°C/72 h). Peak times at 30°C were considerably shorter than those at 21°C. The correlation between both plate count methods and the peak times were better when measuring at 21°C than at 30°C. Significant correlations between HPRs and colony counts were obtained with all experimental conditions. Results indicate that micro-calorimetric measurements of 10^-1 NB suspensions of ground meat provide a promising analytical tool for estimation of the bacterial levels in less than 24 h in the range of 10⁵ to 10⁸ CFU/g.