Total Phenolic and Flavonoid Content, Antioxidant Activity of Talaromyces funiculosus Strains

Abstract

Microscopic fungi synthesize a wide range of phenolic compounds that play an important role in cell wall formation, as well as perform signaling and protective functions. One of the important functions of phenolic compounds, primarily polyphenols, is antioxidant activity. The most active polyphenols are flavonoids, their synthesis in microscopic fungi has not been studied enough. The aim of the study was to determine the total phenols and flavonoids content and antioxidant activity of Talaromyces funiculosus strains isolated from different econiches. Methods. 20 strains of the microscopic fungus T. funiculosus – 10 endophytes and 10 saprotrophs were used in the experiments. Cultivation of filamentous fungi was performed under submerged conditions with shaking at 210–230 rpm in Erlenmeyer flasks containing 200 ml of Czapek liquid medium at a temperature 26±2°C for 6 days. The biomass of the strains was filtered, dried at 70°C and extracted with 95% methanol (1:50 w/v). The total phenols content was determined using Folin-Ciocalteu reagent by the method of Arora, Chandra (2010) with some modifications and expressed as mg of gallic acid equivalents (GAE) per g of dry weight mycelium. Flavonoids in each extract were determined spectrophotometrically with AlCl3 and expressed as mg of quercetin equivalents (QE) per g of dry weight mycelium. Antioxidant activity of methanolic extracts was measured as radical scavenging activity by the percentage inhibition of the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical. Results. The total phenolic content of methanolic extracts of T. funiculosus strains ranged from 0.12±0.007 to 1.97±0.150 mg GAE/g. The highest level of phenolic compounds was found for saprotroph UCM F-16790 (1.97±0.150) and endophyte UCM F-16795 (1.71±0.137 mg GAE/g). The flavonoid content in methanolic extracts of the studied strains varied in the range of 0.02±0.001–0.39±0.041 mg QE/g. All studied strains of T. funiculosus showed antioxidant activity against DPPH radical, which was 12.19±2.34–60.37±7.24% inhibition. Statistical analysis revealed a strong positive correlation between the total phenols and flavonoids content (Pearson’s correlation coefficient r=0.92); between antioxidant activity, phenols (r=0.82) and flavonoids (r=0.81) content in methanol extracts of T. funiculosus strains. The total content of phenols and flavonoids and antioxidant activity did not depend on the trophic group of the studied strains. The moderate correlation between flavonoids content and antioxidant activity of methanolic extracts of endophytic T. funiculosus strains (r=0.46) may be related to their ability to synthesize a wider range of polyphenolic compounds with antioxidant activity. Conclusions. The studied T. funiculosus strains have the ability to synthesize phenolic compounds and flavonoids in different concentrations. Correlation analysis revealed strong correlations between total phenolic and flavonoid contents and antioxidant activity. The reason for phenomenon of moderate correlation (r=0.46) between flavonoid content and antioxidant activity in endophytic strains may be the synthesis of other compounds by individual strains. The determination of individual components synthesized by the most active strains is of scientific interest for further study. T. funiculosus UСM F-16795 and UСM F-16790 strains had a quite high level of phenols and flavonoids. Obtained data may be promising for the search for phenolic compounds with antioxidant properties to increase plant resistance to negative impacts of environmental stress factors.