The allergenicity of glycerol esters and other esters of rosin (colophony).

To investigate whether esterification of rosin with polyalcohols changes its allergenic potential, abietic acid, the main component of rosin, was esterified with glycerol at high temperature. The major product formed was isolated and identified, using nuclear magnetic resonance (NMR), infra-red (IR) and mass spectrometry (MS) analyses, as glyceryl triabietate (GTA), an ester between one glycerol molecule and 3 abietic acid molecules. According to animal experiments GTA was not allergenic and no cross-reactivity was seen to allergens in unmodified rosin. When testing patients allergic to unmodified rosin, no reactions were found to GTA. Some of the patients reacted to glycerol- and pentaerythritol-esterified rosins. According to HPLC analyses, these esterified rosins still contained unmodified material to which the patients may have reacted. It seems that the esterification of rosin with polyalcohols such as glycerol reduces its allergenic activity, possibly because of the formation of much larger molecules with reduced bioavailability. However, making methyl esters of rosin causes little alteration in the molecular weights of the components and, when unmodified and methylated rosin were tested in patients, we saw no difference between the 2 forms.