Evaluation of BactoScan FC for the enumeration of bacteria in raw milk

The evaluation of BactoScan FC for routine enumeration of bacteria in raw m ilk was carried out according to the model proposed by the International Da iry Federation. The linearity of response of BactoScan FC was verified betw een 6 000 and 27 000 000 pulses.mL(-1) without reaching the limits of detec tion which have not been determined. The transmission error was estimated a t 0.09% and the repeatability at 0.084 log(10) CFU.mL(-1) for a 60 000 CFU. mL(-1) mean level of contamination. The stability of the equipment over tim e was verified; in both the short term and the long term, reproducibility i s in the same order of magnitude as repeatability. The relationship between BactoScan FC and the reference method is linear over the whole range analy sed (700 to 26 000 000 CFU.mL(-1)), with a determination threshold estimate d at under 4 000 CFU.mL(-1). The regression equation between the reference method and the BactoScan FC is: log(10) (CFU.mL(-1)) = 0.839 x log(10) (pul ses.mL(-1)) + 0.095. The accuracy of estimation of the reference value, exp ressed by the residual standard deviation of the regression, is 0.287 log(1 0) CFU.mL(-1). Finally, the independence of this estimate compared to the s omatic cell level of the samples was verified.