Setting up reliable analytical methods for quality evaluation of propolis: a proficiency study within the ISO/TC 34/SC 19 “Bee products”

The establishment of international standards require the use of analytical procedures able to produce reliable outputs with good levels of repeatability and reproducibility. The propolis working group of the technical subcommittee of International Standard Organization, ISO/TC 34/SC 19 – WG2, is designing the first international standard for propolis, and setting specific quality parameters for ethanolic extractable, loss on drying, ash, wax content, total phenolic and total flavonoids content, phenolic profile and antioxidant capacity. In order to define reliable parameters, an interlaboratorial trial was set up with 14 laboratories around the globe, under the supervision of an independent organization, and researching on three types of samples: brown propolis from Populus, green from Baccharis and red from Dalbergia/Symphonia/Clusia. The majority of the laboratories presented consistent results, with the coefficient of variation below 20%, and even below 10% for the ethanolic extraction ash and wax. With this work, it was possible to establish minimum/maximum limits for each parameter as move a step forward to standardize propolis in the international trade.