Evaluation of antioxidant properties of some commercially available culinary and medicinal mushrooms from Taiwan

Abstract

A selection of commercially available mushrooms was obtained from Taiwan and screened for phenolic contents and antioxidant activity in aqueous extracts using various chemical measurements, namely scavenging of 2,2´-azinobis-(3-ethylbenzothiazoline-6-sulphonate) radical cation (TEAC), Ferric reducing antioxidant power (FRAP), scavenging of 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) and Folin-Ciocalteu reaction. According to the antioxidant activity perceived, Cordyceps militaris, Pleurotus citrinopileatus, Trametes versicolor, Hericium erinaceus, Ganoderma lucidum and Auricularia auricula-judae were selected for in vitro digestion and cellular antioxidant assay. After the in vitro digestion steps, the antioxidant activity in the extracts of C. militaris had significantly decreased, (in TEAC 22% and 27 % decrease, in hot- and cold-water extracts, respectively, in FRAP 42% and 21% decrease, in hot- and cold-water extracts, respectively and in DPPH 78% and 21% decrease in hot- and cold-water extracts, respectively). The hot-water extract of A. auricula-judae and cold-water extracts of H. erinaceus showed no significant increase in TEAC assay after enzymatic digestion. There was a significant increase in antioxidant activity in the other mushroom extracts after in vitro enzymatic digestion. P. citrinopileatus exhibited the most potent antioxidant activity in the TEAC (from 24 to 2 times higher and 10 to 1.5 times higher than other mushrooms in hot- and cold-water extracts, respectively) and DPPH assays (from 6.4 to 1.2 times higher and from 27 to 1.6 times higher than the other five mushrooms in hot- and cold-water extracts, respectively) after digestion steps. T. versicolor showed the most potent ferric reducing power after digestion steps (from 29 to 5 times higher and 14 to 1.1 times higher than the other five mushrooms in hot- and cold-water extracts, respectively). These results indicate that most of the potential antioxidant compounds within the mushroom extracts could be released after digestion steps, whereas the potential antioxidant compounds of C. militaris might be degraded after digestion steps. The results suggest that determination of antioxidant activity in selected mushroom extracts may underestimate the real antioxidant activity that may be in close contact with the intestinal lumen. Chemical estimates of potential antioxidant compounds within the mushroom extracts may not accurately indicate the complex nature of the antioxidant activity of mushroom extracts within cells. In this study, human hepatoma cell lines (Huh 7) were used to measure cellular antioxidant activity using 2´, 7´- dichlorodihydrofluorescein diacetate as a fluorescent probe. In artificially induced peroxyl radicals, among the selected mushroom extracts tested, C. militaris and T. versicolor had the highest cellular antioxidant activity, whereas H. erinaceus had the lowest. In addition, in chemical assays (TEAC and DPPH), the antioxidant activity of T. versicolor was less than that of P. citrinopileatus (64% and 67 % less in TEAC in hot-and cold- water extracts, respectively and 70% and 82% less in DPPH in hot- and cold-water extracts respectively). Even though the antioxidant activity of C. militaris was decreased after digestion steps, C. militaris exhibited far stronger cellular antioxidant activity than the other five mushrooms (p < 0.001). Based on the different antioxidant assay methods, the antioxidant activity of each antioxidant assay gave different antioxidant trends and antioxidant activity value depending on the type of extract method (hot- and cold-water extracts). Using cellular antioxidant assays may produce bioactivity results of the antioxidant activity of mushroom extracts within cells. These findings could suggest that the aqueous extracts from C. militaris and T. versicolor associated with health benefits and other traditional remedies, at least in part, might be their potent antioxidant activity.