Industrial Crops and Products 61 (2014) 430–437 Contents lists available at ScienceDirect Industrial Crops and Products jo u r n al homep age: www.elsevier.com/locate/indcrop 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 Sauro Bianchi a,∗ , Alexia N. Gloess b , Ivana Kroslakova b , Ingo Mayer a , Frédéric Pichelin a a Bern University of Applied Sciences, Architecture Wood and Civil Engineering, Solothurnstrasse 102, CH-2502 Biel, Switzerland b Zurich University of Applied Sciences, Institute of Chemistry and Biological Chemistry, Einsiedlerstrasse 31, CH-8820 Wädenswil, Switzerland a r t i c l e i n f o Article history: Received 28 March 2014 Received in revised form 8 July 2014 Accepted 18 July 2014 Keywords: Abies alba Picea abies Bark Condensed tannins MALDI-TOF a b s t r a c t 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. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The condensed tannins, or proanthocyanidins, are polyphenolic compounds present in bark, heartwood, roots, leaves and fruits of several plant species (Haslam, 1989). Aside from their traditional use in the leather industry, water extracted condensed tannins have been proven as suitable natural sourced chemicals for the formu- lation of formaldehyde-free wood adhesives (Pichelin et al., 1996, 2006; Kim and Kim, 2004; Pizzi, 2006), foamed materials (Tondi and Pizzi, 2009; Lacoste et al., 2013) and rigid composites (Sauget et al., 2013). Condensed tannins extracted from tropical species such as Black wattle (Acacia mearnsii [De Wild.]) and Quebracho (Schinopsis lorentzii [Engl.]), and from the softwood Radiata Pine (Pinus radi- ata [D. Don]) are the most available and industrially used products (Pizzi and Merlin, 1981; Pizzi, 1982; Sealy-Fisher and Pizzi, 1992; Pizzi et al., 1993; Pizzi and Stephanou, 1994; Valenzuela et al., ∗ Corresponding author. Tel.: +41 32 344 02 79; fax: +41 32 344 03 91. E-mail addresses: sauro.bianchi@bfh.ch, saurbian@gmail.com (S. Bianchi). 2012). The bark of European softwoods has also been recognized as a source of condensed tannins (Porter, 1989; Matthews et al., 1997; Jerez et al., 2009; Navarrete et al., 2010; Krogell et al., 2012; Ucar et al., 2013; Chupin et al., 2013; Abdalla et al., 2014), which have been proven to be effective in wood-adhesive formulations (Liiri et al., 1982; Dix and Marutzky, 1987; Yazaki and Collins, 1994; Pizzi, 1998; Roffael et al., 2000; Bertaud et al., 2012). Today, soft- wood bark is considered a side-product of the wood industry and is generally disposed of as fuel or in horticulture. Extraction of tannin from European softwood bark could therefore represent a useful valorization of such a resource. Chemically, the condensed tannins have been identified as oligomers made of flavan-3-ol monomeric units linked by C C bonds. The mean degree of polymerization of the extracted oligomers has been reported between 2 and 15 (Porter, 1992). The most common monomers were identified as fisetinidol, robine- tinidol, catechin, gallocatechin and their correspondent epimers (Fig. 1). These monomers represent the dominant building blocks of the oligomers profisetinidin, prorobinetinidin, procyanidin and prodelphinidin, respectively. The presence of methyl or glucosyl http://dx.doi.org/10.1016/j.indcrop.2014.07.038 0926-6690/© 2014 Elsevier B.V. All rights reserved.