Modification of AOAC Official Method[SM] 998.12 to add filtration and/or centrifugation: interlaboratory comparison exercise

An international ring test was undertaken in 2012 among 10 international honey testing laboratories to examine the effects of filtration and/or centrifugation addition to AOAC 998.12 method (C4 sugar detection in honey). During protein extraction, when using the repetitive washing method, any insoluble material (i.e., pollen, dust) is coextracted along with protein which may result in contamination of the protein isotope value and result in a false-positive test. A modification step involving filtration and/or centrifugation to remove insoluble material before protein flocculation was proposed. Results were compared across 10 laboratories internationally and were found to be an excellent assessment of interlaboratory variability with the standard variances between laboratories better than [+ or -] 0.2[per thousand] for honey and [+ or -] 0.3[per thousand] for protein.