Produção de material de referência para ensaio de proficiência de enumeração de Bacillus cereus em leite

The participation in proficiency testing (PT) is essential for testing laboratories to prove their technical competence. The aim of this study was to produce a quantitative reference material (RM) for PT containing Bacillus cereus in milk powder. A sterile solution of 10% skim milk containing 100 mM sucrose was contaminated with a B. cereus strain in a specific concentration. The homogenized matrix was distributed into vials and freeze-drying. The batch produced was considered sufficiently homogeneous assigning a target standard deviation of 0.25. The RM was stable at ≤ -70 oC and (-20 ± 4) oC for 1,058 and 60 days, respectively. In the evaluation of temperatures for the transport of material, the RM was stable at 4, 25 and 35 oC during four days. It is  concluded that the batch produced had all the necessary requirements to be used as items of PT.