Effects of UV Stress in Promoting Antioxidant Activities in Fungal Species Trametes versicolor (L.) Lloyd and Flammulina velutipes (Curtis) Singer

Trametes versicolor and Flammulina velutipes, after submerged cultivation, with intermittent exposure to ultraviolet light (UV), were studied for Total Phenolic content (TP) and Total Proteins (TPR) contents and antioxidant properties against free radicals. The TP and TPR were determined by a spectrophotometric method and Lowry's assay, respectively. Liquid chromatography with mass spectrometry (LC-MS/MS) was used to quantify polyphenols. Different in vitro assays determined the antioxidant activities of the extracts. Mycelia extract from F. velutipes after 14 days and filtrate from T. versicolor after 21 days of incubation gave the highest TP 59.60 +/- 0.14 and 50.03 +/- 0.66 mg GAE/g d.w., respectively. Mycelia extract from T. versicolor after 28 days of incubation had the highest TPR (183.53 +/- 2.84 mg BSAE/g d.w.). The LC-MS/MS analysis indicated that p-hydroxybenzoic and protocatechuic acids are the most abundant. Trametes versicolor filtrate after 14 days and F. velutipes filtrate after 21 days (71.29 +/- 0.54% and 73.5 +/- 1.81, respectively) had the highest scavenging activity in SOA. Correlation analysis indicated that all extracts' antioxidant (AO) potential strongly correlated with TP (R-2 = 0.83-1.0). The data confirmed that stress factors such as UV exposure could stimulate the production of secondary metabolites and natural AOs, especially phenolic acids in test fungi.