Development of a reference material for Staphylococcus aureus enterotoxin A in cheese: feasibility study, processing, homogeneity and stability assessment.

Staphylococcal food poisoning is caused by enterotoxins excreted into foods by strains of staphylococci. Commission Regulation 1441/2007 specifies thresholds for the presence of these toxins in foods. In this article we report on the progress towards reference materials (RMs) for Staphylococcal enterotoxin A (SEA) in cheese. RMs are crucial to enforce legislation and to implement and safeguard reliable measurements. First, a feasibility study revealed a suitable processing procedure for cheese powders: the blank material was prepared by cutting, grinding, freeze-drying and milling. For the spiked material, a cheese-water slurry was spiked with SEA solution, freeze-dried and diluted with blank material to the desired SEA concentration. Thereafter, batches of three materials (blank; two SEA concentrations) were processed. The materials were shown to be sufficiently homogeneous, and storage at ambient temperature for 4weeks did not indicate degradation. These results provide the basis for the development of a RM for SEA in cheese.