Preparation of a reference material containing sterigmatocystin

Abstract

To assure the homogeneity of a reference material for the mycotoxin sterigmatocystin (STE), a study was first conducted to prepare a reference material of rice containing the colouring Food Red 106. The protocol developed was then used to prepare a reference material of rice containing STE. Initially, a V-shaped mixer was used to mix Food Red 106 and ground brown rice, but the resulting mixture was non-homogeneous. However, when a ShakeMaster was used for the simultaneous grinding and mixing of brown rice with Food Red 106, good homogeneity was obtained. Accordingly, a dried culture of Aspergillus versicolor NRRL5219 and brown rice was ground and mixed with the ShakeMaster. To assess the distribution of the STE an Autoprep® MF-A 1000 mini-column was used to isolate the STE, and a 115–120% recovery rate was obtained. Repeatability (variability within a day) and intermediate precision (variability between days) were good. According to the IUPAC/ISO/AOAC International Harmonized Protocol for the Proficiency Testing of Analytical Chemistry Laboratories, a homogeneous candidate reference material was obtained. The particle sizes of ground brown rice, ground brown rice containing Food Red 106, and ground brown rice containing a non-STE producing culture of A. oryzae were analysed and they ranged from 10 to 700 µm.

Keywords:

• sterigmatocystin
• reference material
• ShakeMaster
• Food Red 106
• particle size distribution

Acknowledgements

The authors acknowledge Dr Steve Peterson of the USDA-ARS-NCAUR for providing A. versicolor strains capable of producing sterigmatocystin. They are thankful to Dr Nozawa in Kishikasei, Inc. for kindly providing Food Red 106. They are thankful to Dr Kenji Taketomi, Dr Satoshi Akiyama, Dr Kazumi Kozawa, and Dr Tatsurou Maeda, Nissin Seifun Group, Inc., for advice on the grinding and shaking methods, and the particle size distribution analyses. They are thankful to Ms Hiroko Noriduki, Japan Grain Inspection Association, for advice on shaking of samples to make them homogeneous. They are thankful to Dr Ken’ichi Ohtsubo, Niigata University, for advice on sample mixing with the S-3 V-shaped shaker. They are thankful to Dr Tatsuo Suzuki, Dr Takaho Watanabe and Ms Noriko Takasaka, Hatano Research Institute, Food and Drug Safety Center, for advice on the shaking of the samples to make them homogeneous. This work was supported by a grant-in-aid (Development of Evaluation and Management Methods for Supply of Safe, Reliable, and Functional Food and Farm Produce) from the Ministry of Agriculture, Forestry and Fisheries of Japan.