Phenolic composition and antioxidant properties of Pleurotus ostreatus and Pleurotus eryngii enriched with selenium and zinc

The aim of the study was to investigate the antioxidant properties, phenolic and flavonoid contents and composition and content of ascorbic acid in Pleurotus ostreatus and Pleurotus eryngii enriched simultaneously with selenium (Se) and zinc (Zn). Non-enriched mushrooms contained Se and Zn at the level as in the most popular mushrooms. The total phenolic content (TPC) for non-enriched P. ostreatus and P. eryngii was 9.64 ± 0.33 and 7.91 ± 1.02 mg/g of extract, the total flavonoid content was 2.11 ± 0.19 and 1.26 ± 0.17 mg/g of extract, and ascorbic acid content ranged from 10.28 ± 0.39 to 16.64 ± 0.47 mg/100 g DW, respectively. Methanolic extracts contained 4-hydroxybenzoic, ferulic, p-coumaric, protocatechuic, t-cinnamic and vanillic acids and naringenin. In methanolic extract of P. eryngii, 2,5-dihydroxybenzoic acid was also quantified. The correlation between the TPC and antioxidant activity in mushroom was confirmed. Additionally, the correlations between Zn and Se concentration in fruiting bodies and EC50 value and phenolic compounds were confirmed. Our results with simultaneous supplementation with Zn and Se provide the opportunity to increase the content of the elements in fruiting bodies and to improve antioxidant properties and antioxidant contents in enriched mushrooms. Additionally, the obtained results demonstrated that simultaneous enrichment with micronutrients with a contrary effect on antioxidant properties can activate synthesis of phenolic compounds and ascorbic acid. The investigation is the first study evaluating the effect of addition of two elements to the substrate at the same time on antioxidant properties of mushrooms.