Introduction: Cereulide toxin, a cyclic dodecadepsipeptide, is produced by Bacillus cereus and is a causative agent in food-borne outbreaks (FBOs). More than 470 FBOs related to B.c. toxins have been reported in 2023 (European Union One Health Zoonoses Report, EFSA and ECDC). Insufficient hygiene practices are the main reasons for intoxications. Cereulide affects several foods, including starch-rich foods such as pasta and rice. Along with validated methods and proficiency testing schemes, certified reference materials (CRMs) are key to ensure reliable measurements. The JRC aimed to produce a rice CRM containing cereulide at a low ng/g concentration.
Methods: Highly pure cereulide (Chiralix; Nijmegen, NL) was used to spike cooked rice. Thereafter, a rice powder candidate CRM was processed, which exhibits appropriate homogeneity and short-term stability. A characterisation exercise with ten expert laboratories using LC-MS/MS methods mostly based on ISO 18465 (Microbiology of the food chain – quantitative determination of emetic toxin (cereulide) using LC-MS/MS) was carried out. Each laboratory was requested to analyse nine independent sample replicates together with two QC samples (blank rice powder and rice powder contaminated at a very low cereulide concentration) under intermediate precision conditions.
Results: First, the measurement results were technically scrutinised. Some data sets had to be excluded from further evaluation (e.g. working range of method inadequate, QC results incorrect, and non-adherence to the provided instructions). After statistical evaluation, it could be concluded that the laboratory mean results were about normally distributed. No mean and variance outliers were detected. The mean of laboratory means amounted to 11.25 μg cereulide per kg rice, with an uncertainty related to characterisation of 0.23 μg/kg (2.04 %).
Conclusion: Once long-term stability data is available, a full uncertainty budget will be drawn up. The CRM will be used for method validation and quality control; therefore, it will enable laboratories to set up and safeguard reliable cereulide measurements in food and facilitate effective consumer protection.
