Abstract
Phenolics and extracted phenolic compounds of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) show antibacterial activity against several bacteria. The majority of phenolic compounds are stilbenes, flavonoids, proanthocyanidins, phenolic acids, and lignans that are biosynthesized in the wood through the phenylpropanoid pathway. In Scots pine (P. sylvestris), the most abundant phenolic and antibacterial compounds are pinosylvin-type stilbenes and flavonol- and dihydroflavonol-type flavonoids, such as kaempferol, quercetin, and taxifolin and their derivatives. In Norway spruce (P. abies) on the other hand, the main stilbene is resveratrol and the major flavonoids are quercetin and myricetin. In general, when the results from the literature regarding the activities of flavonoid glycosides and their aglycones against a total of twenty-one microorganisms are summarized, it was found that phenolic glycosides are less active than the corresponding aglycones, although a number of exceptions are also known. The aglycones in plants respond to various kinds of biotic stress. Synergistic effects between aglycones and their glycosides have been observed. Minimum inhibition concentrations of below 10 mg L−1 against bacteria have been reported for gallic acid, apigenin, and several methylated and acylated flavonols present in these industrially important trees. In general, the phenolic compounds are more active against Gram-positive bacteria, but apigenin is reported to exhibit strong activity against Gram-negative bacteria. The present review lists some of the biosynthesis pathways for the antibacterial phenolic metabolites found in Scots pine (P. sylvestris) and Norway spruce (P. abies). The antimicrobial activity of the compounds is collected and compared to gather information about the most effective secondary metabolites.
Highlights
Utilization of wood-based compounds, extracts, and biomass has increased enormously (Rauha et al 2000; Jansson et al 2013; Boden et al 2014; Ganthaler et al 2017)
Phloem, and needles of Scots pine (P. sylvestris) stilbenes accumulate in the tree to defend biotic stress after wounding, fungal attack, and ozone intake, which increases the amount of oxygen in the wood and enables the compound reactions chemically with oxygen (Gehlert et al 1990; Zinser et al 1998; Rosemann et al 1991)
Most of them are produced via the phenylpropanoid pathway by the involvement of several plant enzymes, synthases, transferases, reductases, and hydroxylases
Summary
Utilization of wood-based compounds, extracts, and biomass has increased enormously (Rauha et al 2000; Jansson et al 2013; Boden et al 2014; Ganthaler et al 2017). The industrial use of wood components has increased and even extracts are used as starting fluids and mixtures in health products and industrial chemicals including botulin, furfural derivatives, stilbens, tannins, flavonoids, tall oil, and resin (Roitto et al 2008; Royer et al 2012; Long et al 2013). The phenolic compounds of low molecular weights may originate from hydrolysis of the wood due to degradation of the material and are not the extractives from the wood. Another determinant is the analysis method used to identify and characterize the wood compounds. When sample manipulation, such as derivatization, is used to improve the sensitivity to reach the methodological levels of the instruments, the originality of the sample matrix is lost
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