Propolis is a resinous beehive product with extraordinary bioactivity and chemical richness,
linked with the botanical sources of the resin. The potential of this product keeps captivating
the scientific community, conducting to continuous and growing research on plant sources,
composition, or applications in agriculture, cosmetics, pharmacy, odontology, etc. In all cases,
the quality assessment is a requirement and relies on methods to extract the bioactive substances
from the raw propolis and quantify different components. Unfortunately, besides the
absence of international quality requirements, there is also a lack of standardized analytical
procedures, despite the presence of several methodologies with unknown reliability, often not
comparable. To overcome the current status, the International Honey Commission established
an inter-laboratory study, with propolis samples from around the globe, to harmonize analytical
methods and evaluate their accuracy. A common set of protocols was matched between
twelve laboratories from nine countries, for quantification of ash, wax, and balsamic content in
raw propolis, and spectrophotometric evaluation of total phenolics, flavone/flavonol, and flavanone/
dihydroflavonol in the extract. A total of 3428 results (97% valid data), were used to
assess the methods’ accuracy following ISO-5725 guidelines. The within-laboratory precision,
revealed good agreement levels for the majority of the methods, with relative variance below
5%. As expected, the between-laboratory variance increased, but, with exception of the flavanone
method that revealed a clear lack of consistency, all the others maintained acceptable
variability levels, below 30%. Because the performance of ultrasounds procedures was low,
they cannot be recommended until further improvements are made.
The authors are grateful to the Foundation for Science and
Technology (FCT, Portugal) for financial support by
national funds FCT/MCTES to CIMO (UIDB/00690/2020).
Thanks to the Programa Apíıcola Nacional 2020-2022
(National Beekeeping Program) for funding the project
"Standardization of production procedures and quality
parameters of bee products" and to Project PDR2020-1.0.1-
FEADER-031734: “DivInA-Diversification and Innovation on
Beekeeping Production”. National funding by FCT –
Foundation for Science and Technology, through the institutional
scientific employment program-contract with
Soraia I. Falcão. A special thanks is given to Hartmut
Scheiter and Allwex Food Trading GmbH, Bremen,
Germany, for providing, handling and delivering the propolis
blind samples.
