Preparation of Reference Material for Proficiency Test for Enumeration of Coliforms in Cheese Matrix

Marcelo Luiz Lima Brandão, Carla de Oliveira Rosas, Silvia Maria Lopes Bricio, Valéria de Mello Medeiros, Juliana de Castro Beltrão da Costa, Rodrigo Rollin Pinheiro, Paola Cardarelli-Leite, Marcus Henrique Campino de La Cruz, Armi Wanderley da Nóbrega

Laboratory of Products, Department of Microbiology, National Institute of Quality Control in Health, Oswaldo Cruz Foundation, Rio de Janeiro, Brazil.
Proficiency Testing Program of Products Subject to Health Surveillance, National Institute of Quality Control in Health, Oswaldo Cruz Foundation, Rio de Janeiro, Brazil.

DOI: 10.4236/detection.2013.11002                

Abstract

It is widely accepted that quantitative reference materials (RM), are indispensable tools for verification of the precision and accuracy of analytical measurements. The RM can be used by food microbiology laboratories, as part of their quality assurance programmes, to achieve their quality control. In Brazil, Anvisa RDC No. 12/01 specifies the enumeration of coliforms as one of the parameters for evaluating cheese quality. The aim of this study was to produce a quantitative RM for proficiency testing (PT) for use in the testing of enumeration of coliforms in cheese matrixes. A sample of an ultra-filtered cheese with a coliforms count of <3.0 MPN/g and a total n? of viable aerobes of 1.2 × 103 CFU/g was used as the matrix to produce the RM. The ultra-filtered cheese matrix was distributed in flasks, contaminated with a specific concentration of an Escherichia coli strain and submitted to freeze-drying. Sucrose was used as the cryo-protector. The RM produced was considered sufficiently homogeneous and stable at ≤ ?70?C during the entire study period (348 days). The material was also considered sufficiently stable at 4?C for six days, but instable at 30?C and 35?C for the same period. At ?20?C the RM was sufficiently stable for 161 days. It was concluded that the material showed all the necessary requirements for a quality RM to be used as PT items and could be transported to the laboratories taking part in a PT at up to 4?C for up to 6 days, since the results indicated maintenance of the cell concentrations during this period. This is the first study to describe a methodology for producing RM containing coliforms in a cheese matrix.

Keywords

Coliforms; Cheese; Reference Material; Proficiency Test

Conflicts of Interest

The authors declare no conflicts of interest.

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