Potential occurrence of adhering living Bacillus spores in milk product processing lines

Aims: The hygienic risk associated with microbial soil on surfaces of milk processing lines was evaluated, based on experimental results. Methods and Results: From a panel of Bacillus spores isolated from milk products, B. cereus CUETM 98/4, was found to be highly resistant to heat (D-100 = 3.32 min in whole milk) and oxidant disinfectant (70% lethality of adherent spores with Ikalin 2%). From adhesion trials, up to 1.1 x 10(7) spores cm(-2) were found to be adherent to solid surfaces when suspended in saline or in custard (10(5) and 10(7) cfu ml(-1)), and over 10% of these adherent spores would resist the cleaning procedure. Conclusions: A highly contaminated milk (10(5) cfu ml(-1)) subjected to a current sterilization process (8 log reduction) led to a residual contamination of less than 1 cfu in the representative processing line after a complete production run. Significance and Impact of the Study: This study highlighted the fact that under appropriate processing conditions (efficient sterilization and cleaning procedures), even disinfection would be sufficient to eliminate any contamination risk. Conversely, the disinfection procedure becomes an essential step under inappropriate processing conditions.