Estimation of microbiological quality of chilled beef using automated turbidimetry

Total bacterial counts on chilled beef samples were estimated by the standard plate count method and by an automated turbidimetric system. The latter method is based on product-specific calibration curves constructed by correlating growth curve parameters calculated for the turbidimeter to the log CFU values obtained by plate counts. A total of 74 beef samples was used to construct the calibration curves. Correlation analysis between turbidimetric parameters and plate count values showed that detection time was the best predictor to estimate microbial loads on fresh (r = 0.91) and aged beef (r = 0.94). Microbial loads for a different set of aged beef samples (n =37) refrigerated for 7, 9, 10, 17 and 45 days were compared by turbidimetric measurements and plate counts. Mean total viable counts were log 5.92 +/- 1.17 and log 5.54 +/- 1.28 CFU/mL, respectively. Results showed that total bacterial counts on chilled beef could be estimated accurately from turbidimetric parameters. Furthermore, setting a cut-off value of log 6 CFU/mL allowed to accepting/rejecting samples according to their microbial condition in shorter periods of time compared to the traditional plate count method.