Lignicolous fungi hydrodistilled extracts may represent a promising source of natural phenolics

Abstract In vitro evaluation of total phenolic contents and antiradical activities of the lignicolous fungi Fomes fomentarius and Schizophyllum commune hydrodistilled extracts was the subject of this study. This preliminary screening included four free radical species evaluated by UV–vis (DPPH•, ABTS• and •NO) and EPR (Asc•), respectively. According to the experimental data obtained, both F. fomentarius and S. commune hydrodistilled extracts may be considered as promising sources of phenolic natural products (157 and 138 mg GAE/g d.e., respectively) and other bioactives showing good anti-DPPH (1.31 μg/mL) and anti-Asc (70.40%) radical activities, respectively, at in vitro conditions. Graphical Abstract


Introduction
Due to their enzymatic machineries, lignicolous fungi effectively degrade wood mass which primarily consists of lignin, a polymer phenolic compound (Schmidt 2006;Matavulj et al. 2013). Fomes fomentarius (L.:Fr.) (Polyporaceae), tinder fungus, is a woody perennial fungus which develops as a parasite or saprophyte on the beech (Fagus sylvatica L.) and other deciduous species. It is a white root fungus, large in size which causes heart root of the wood (Větrovský et al. 2011). This genus is known to be a source of bioactive phenolics (He et al. 2003). In traditional Chinese medicine, among the rest, F. fomentarius has been used for the treatment of various inflammations and cancers (Chen et al. 2008). Some research studies have actually confirmed ethnomedicinal claims (Park et al. 2004;Seniuk et al. 2011). Its most important compounds with clinically beneficial activity are β glucans (Grienke et al. 2014) and phenolics (Heleno et al. 2015). Schizophyllum commune Fr.:Fr., split gill fungus, is probably the most widespread existing macroscopic fungus existing on every continent except Antarctica, where there is no wood to be used as a substrate (Matavulj et al. 2013). Though usually considered as a widely distributed basidiomycetous pathogen (Sigler et al. 1999), S. commune has actually been acknowledged for its medical importance (Han et al. 2005). As an edible species, S. commune is widely consumed in Mexico and elsewhere in the tropics (Ruán-Soto et al. 2006). It is also very popular among the Malay community in Malaysia, the country where S. commune has been cultivated for the last ten years (Han et al. 2005). Besides phenolics and some other compounds, this fungus produces the neutral extracellular polysaccharide schizophyllan which possesses potent bioactivities both in vitro and in vivo (Smith et al. 2002;Yim et al. 2009;Tripathi & Bhupendra 2013). Generally speaking, there is a growing interest for natural phenolics, both for their medicinal and nutritional properties (Barros et al. 2009). Hydrodistilled extracts of lignicolous fungi were not the subject of extensive chemical research so far, neither was their biological activity evaluated to a greater extent. That was the reason why the total phenolic (TP) contents and antiradical activities (DPPH • , ABTS • , • NO and Asc • ) of the hydrodistilled extracts of these fungi were tested (Green et al. 1982;Singleton et al. 1999;Espín et al. 2000;Arnao et al. 2001). The choice of their particular representatives to be screened was primarily made on the basis of available ethnomedicinal records (which point out the use of the fruiting bodies) and global distribution. Indeed, the aim was to check out if this type of lignicolous fungi extracts has potential to be considered as a good source of natural antioxidants to be eventually used in medicine, pharmacy and/or food industry.

Results and discussion
TP content ranged from 138 to 157 mg GAE/g d.e. for S. commune and F. fomentarius hydrodistilled extracts, respectively (Table 1); the latter value is ≈ 2 × higher than the obtained one for the ethanol extract (82.54 mg GAE/g d.e.) of the same fungal species (F. fomentarius; originating from different habitat, Novi Sad-Serbia) performed in a common way excluding the hydrodistillation step (Karaman 2009). Nowacka et al. (2015) have recently reported relatively similar TP content (53.13 mg GAE/g d.e.) for the Polish F. fomentarius (collected in Lublin Province) ethanol extract performed in a standard way. Finally, the water extract of the same fungus originating from Iran contained 9.90 μg GAE/100 μg extract (Vazirian et al. 2014). On the other hand, Indian researchers have found 12.50 μg GAE/mg of dry extract (d.e.) in the common S. commune ethanol extract (Devi et al. 2014). Furthermore, TP contents of the methanol and water extracts of S. commune (purchased from local markets in Malaysia) were reported to be 1.72 and 0.52 mg GAE/g of dry extracts, respectively (Mirfat et al. 2010). The use of hydrodistillation which destroys sporoderm of the fungal hymenia resulting in translocation of great amount of phenolics stored in the spores may partially explain such a result. The quantitative differences observed are also likely to be related to the places of harvesting and climatic conditions. While the examined F. fomentarius extract was the most active towards DPPH radical (1.31 μg/mL), the S. commune hydrodistilled extract was found to exhibit the highest antiradical potential against Asc radical (70.40%) ( Table 1). In comparison, Karaman et al. (2014) have pointed out an 8-fold less anti-DPPH radical activity ( ≈ 10.70 μg/mL) for the F. fomentarius ethanol extract obtained by standard procedure.

Experimental
See supplementary material for more information.

Conclusion
Taken all together, both F. fomentarius and S. commune hydrodistilled extracts may be considered as enhanced resources of natural phenolics and other bioactive substances with antiradical potential to be used in medicine, pharmaceutical and/or food industries.

Disclosure statement
No potential conflict of interest was reported by the authors.