An integrated characterization of Picea abies industrial bark regarding chemical composition, thermal properties and polar extracts activity

PLoS One. 2018 Nov 27;13(11):e0208270. doi: 10.1371/journal.pone.0208270. eCollection 2018.

Abstract

The present work determines the chemical and thermal characteristics as well as the phytochemical and antioxidant potential of the polar extractives of the Picea abies bark from an industrial mill, their wood and bark components and also different bark fractions obtained by mechanical fractionation (fine B1, Φ<0.180 mm, medium B3, 0.450 < Φ<0.850 mm and coarse B6, 2 < Φ<10 mm). The aim is to increase the knowledge on the Picea abies bark to better determine possible uses other than burning for energy production and to test an initial size reduction process to achieve fractions with different characteristics. Compared to wood, bark presented similar lignin (27%), higher mineral (3.9% vs 0.4%) and extractives (20.3% vs 3.8%) and lower polysaccharides (48% vs 71%) contents. Regarding bark fractions the fines showed higher ash (6.3%), extractives (25%) and lignin (29%) than the coarse fraction (3.9%, 19% and 25% respectively). Polysaccharide contents increased with particle size of the bark fractions (38% vs 52% for B1 and B6) but showed the same relative composition. The phytochemical profile of ethanol and water extracts presented higher contents for bark than wood of total phenols (2x higher), flavonoids (3x higher) and tannins (4-10x higher) with an increasing tendency with particle size. Bark antioxidant activity was higher than that of wood for ferric-reducing antioxidant power (FRAP, 10 vs 6 mmolFe2+/gExt for the ethanol extract) and free radical scavenging activity (DPPH, 6 vs 18 mg/L IC50 for the ethanol extract) methods. The different bark fractions antioxidant activity was very similar. Bark thermal properties showed a much lower volatiles to fixed carbon ratio (V/FC) than wood (3.1 vs 5.2) although the same higher heating value (20.3 MJ/kg). The fractions were quite similar. Bark presented chemical features that point to their possible upgrade, whether by taking advantage of the high extractives with bioactive compounds or the production potential for hemicellulose-derived oligomers with possible use in nutraceutical and pharmaceutical industries.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Chemical Fractionation / methods
  • Lignin / analysis
  • Minerals / analysis
  • Picea / chemistry*
  • Plant Bark / chemistry*
  • Plant Extracts / chemistry*
  • Polysaccharides / analysis
  • Temperature

Substances

  • Minerals
  • Plant Extracts
  • Polysaccharides
  • Lignin

Grants and funding

The Forest Research Center (CEF) is a research unit funded by Fundação para a Ciência e a Tecnologia (FCT) under UID/AGR/00239/2013. The first author acknowledges a PhD scholarship (PD/BD/52697/2014) under the SUSFOR doctoral program, and the second author a Post Doc scholarship (SFRH/BPD/118743/2016) that are both financed by FCT. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.