Development of rice reference material and its use for evaluation of analytical performance of food analysis laboratories

Data quality is one of the major concerns in development of food composition database and to editors of many peer-reviewed journals in accepting a scientific paper for publication. Regular use of a reference material and participation in a proficiency testing programme could improve the reliability of the analytical data. The objectives of this project were to prepare rice test material with assigned values and to use it to assess the analytical performance of laboratories which are involved in research and analysis of rice. The international guidelines, ISO Guide 35, ISO 13528 and ISO Guide 43, were followed as much as possible throughout the preparation of the reference material and the laboratory performance study. Brown rice (Jasmine variety) was ground to particle size which passed completely through a sieve with pore size 250 μm and packed in laminated aluminum foil bags under vacuum. Based on the analyses of representative nutrients - moisture, protein, iron, zinc and vitamin B1 - the samples were demonstrated homogeneous. Ten expert laboratories from various countries, 36 laboratories from Thailand, and 16 laboratories from ASEAN and Asia registered for the laboratory performance study. The samples were sent for analysis of selected proximate composition (moisture, protein, dietary fibre and ash), two minerals (iron, zinc), and one labile nutrient (vitamin B1) using routine analytical methods. The assigned values of the nutrients in the test materials, as robust mean ± robust SD or predicted SD, were established with their uncertainties. For proximate composition, 67-87% of participating laboratories showed good analytical performance. However, many of them showed questionable and unsatisfactory performance on the analyses of dietary fibre (55%) and vitamin B1 (47%). The evaluation of the results of moisture, protein and iron with their uncertainties against the assigned values of the test material using En score was also demonstrated. Finally, the consensus values of nutrients in the rice sample as mean ± SD were developed from the analytical results of laboratories with good performance for both within- and between-laboratories. This test material can be used as a reference material for internal and external quality control systems to improve the quality of the analytical data.