Propolis from northern California and Oregon: chemical composition, botanical origin, and content of allergens.

Propolis is a beehive product that bees manufacture by mixing their own wax with vegetable resins collected from different species of trees and bushes. The chemical composition of propolis is very variable because it depends on the flora locally available, and specimens from different geographical and climatic areas display unique properties. In this paper, the results of the chemical characterization of some propolis specimens collected in northern California and in Oregon are presented. Their chemical compositions show that all specimens contain resins from poplars of the Tacamahaca section (balsam poplars)--characteristic of the western part of the North American continent. Nevertheless, some of the specimens are of mixed origin because they also contain resins from poplars of the Aigeiros section (cottonwoods)--also present in this part of the world. Propolis causes allergies in sensitive human individuals, which are due to the presence of certain esters. The contents of known propolis allergenic esters--phenylethyl caffeate, 1,1-dimethylallyl caffeate, benzyl cinnamate, and benzyl salicylate--have been investigated in these specimens and found to depend on the botanical origin.