Analysis of the structure of condensed tannins in water extracts from bark tissues of Norway spruce (Picea abies [Karst.]) and Silver fir (Abies alba [Mill.]) using MALDI-TOF mass spectrometry

Abstract

Condensed tannins extracted from the bark of softwoods have been proven to be suitable compounds in the formulation of environmentally friendly adhesives and resins. Their chemical structure has been shown to significantly influence their properties and possible applications. Condensed tannins extracted from the bark of Norway spruce (Picea abies [Karst.]) and Silver fir (Abies alba [Mill.]) still lack a detail characterization of their chemical structure.In an effort to address this deficiency, barks from these species were collected and extracted in water at 60°C. The dried extracts were analyzed by MALDI-TOF mass spectrometry to identify the building blocks and to determine the degree of polymerization of the tannin oligomers. The condensed tannins extracted from spruce bark at the used conditions were mainly composed of procyanidins with a polymerization degree up to 13. Silver fir extracts revealed a predominance of prodelphinidins with a polymerization degree up to 9. The presence of less common building blocks such as stilbene glucosides and flavan-3-ols gallates was also hinted. Different curing times and viscosities in resin formulations are expected between the two studied species, as well as in comparison to the most known and available tannins from tropical species.