Improving Fungal Decay Resistance of Less Durable Sapwood by Impregnation with Scots Pine Knotwood and Black Locust Heartwood Hydrophilic Extractives with Antifungal or Antioxidant Properties

Viljem Vek,Miha Humar,Primož Oven,Ida Poljanšek,Angela Balzano

doi:10.3390/f11091024

Abstract

Research Highlights: The antifungal assay confirmed that knotwood extractives of Scots pine inhibit the growth of wood decay fungi. Heartwood extracts of black locust were found to be much stronger free radical scavengers than the extracts of Scots pine. The extracts were deposited in the lumina and on the wall surface of cells in the impregnated sapwood. Impregnation of the sapwood blocks with Scots pine and black locust extracts reduced the fungal decay of wood. Objectives: Hydrophilic extracts of Scots pine knotwood and black locust heartwood were chemically analyzed, tested for antifungal and antioxidant properties and used for impregnation of beech and Scots pine sapwood. Materials and Methods: Scots pine knotwood and black locust heartwood were extracted, and obtained hydrophilic extractives were chemically analyzed. Extracts were analyzed for antifungal properties with the in vitro well-diffusion method. The free radical scavenging activity of wood extracts was measured colorimetrically. The retention of the extracts in the impregnated sapwood blocks was evaluated with microscopy and gravimetry. A decay test was performed with the mini block test. Results: Almost half of both Scots pine knotwood and black locust heartwood hydrophilic extracts obtained were described by phenolic compounds. The extracts were deposited in the lumina of cells and on the cell wall surface. Extractives of Scots pine knotwood had good inhibitory properties against white- and brown-rot fungi. On the other hand, extractives of black locust heartwood were found to be good radical scavengers, better than knotwood extractives of Scots pine. The extracts of Scots pine knotwood and black locust reduced the fungal decay of the tested sapwood blocks. Conclusions: The results of this research show that the less-valued knotwood of Scots pine and heartwood of black locust are a potential source of antifungal and antioxidant agents for bio-based wood preservatives.

Highlights

Wood is a source of phytochemicals, called extractives, which do not combine with structural components of the cell wall and can be removed with polar and nonpolar solvents [1,2].Wood is a renewable and sustainable polymer composite with several unique properties [3], among which,degradability is considered to be an advantage in biorefining [4,5], for instance, or a disadvantage in applications in which wood is exposed to unfavorable microenvironmental conditions [6]
Our study demonstrated that forestry residues and woods of underutilized tree species should be considered to a greater extent as a potential source of natural bioactive compounds with applicable potentials
Phytochemicals from wood are foreseen in the formulations of preservatives as bioactive agents, they are not at the moment able to compete with synthetic chemicals, characterized by low production costs and long-term efficiency

Summary

Introduction

Wood is a source of phytochemicals, called extractives, which do not combine with structural components of the cell wall and can be removed with polar and nonpolar solvents [1,2].Wood is a renewable and sustainable polymer composite with several unique properties [3], among which, (bio)degradability is considered to be an advantage in biorefining [4,5], for instance, or a disadvantage in applications in which wood is exposed to unfavorable microenvironmental conditions [6]. Impregnation [10,11] or by using more durable woods if available [12]. Formulations for wood preservation currently available for commercial applications are based on copper, with an organic co-biocide added to control copper-tolerant fungi [13,14]. They are considered to be emerging pollutants, and an effort is being made to replace them with environmentally more benign agents. We studied the use of biologically active phytochemicals from Scots pine knotwood and from durable black locust heartwood to protect susceptible woods against fungal decay

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