PhD ThesisA 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