The three reference materials IRMM-359a-c (a blank and two SEA-containing materials) will help laboratories in method validation and method performance verification, and will increase the reliability of measuring SEA in cheese at sub nanogram/gram levels.
They were characterised by laboratories which demonstrated competence to ISO/IEC 17025 and using the European Screening Method with the VIDAS SET2 and the Ridascreen SET Total for detection.
The inter-laboratory comparison saw 13 laboratories in the characterisation study: six used the ESM/VIDAS, five the ESM/Ridascreen and two applied both. More detail on the procedure can be found here.
Link to outbreaks
JRC said the European Food Safety Authority (EFSA) reported in 2014 that bacterial toxins were involved in 843 of 5,251 (16%) food poisoning outbreaks, and Staphylococcal enterotoxins (SEs) were involved in 393 of those 843 notified outbreaks (46%).
SEA is the SE serotype most frequently involved in foodborne staphylococcal illnesses.
Most outbreaks are due to insufficient hygiene practices during processing, cooking or distribution of food. Insufficient cooling can induce coagulase-positive Staphylococci (CPS) growth and stimulate enterotoxin production, potentially resulting in food poisoning.
European legislation (1441/2007) sets out the reference procedure for SE analysis in milk and dairy products, which is based on extraction, dialysis concentration and immunochemical detection using an approved assay.
Results are expressed qualitatively ("sample contains/does not contain SEs").
The minimum sample intake is 15.1g cheese powder (representing 25g after reconstitution) per replicate analysis, as stipulated in the above regulation.
Preparation of material
A raw cow milk cheese, variety Tomme de Savoie, was chosen as base material.
Raw milk cheese was decrusted, cut into cubes, chopped in a kitchen-type food processor for a short time, freeze-dried, cryogenically milled, and mixed (blank material IRMM-359a).
A second portion of raw milk cheese was decrusted and cut into cubes. After adding water and spiking with a solution of SEA, the sample was homogenised using a high-speed grinder (Ultra-Turrax).
The cheese slurry was freeze-dried, cryogenically milled and mixed with blank cheese powder to get the two SEA-containing materials at SEA target levels of 0.1 and 0.25 ng/g cheese, respectively (IRMM-359b, IRMM-359c).
The work was done with the European Union Reference Laboratory (EURL) for Coagulase-Positive Staphylococci, hosted by the French Agency for Food, Environmental and Occupational Health and Safety (ANSES).