Compiled by Initiative Team Member Glenn Cardwell APD
Antioxidant is an umbrella term to cover the range of compounds in the diet that appear to suppress or counter the oxidation of molecules in the body. In using oxygen, the body produces free radicals, a molecule with one or more unpaired electrons. Such a molecule is unstable and tends to steal electrons from other molecules. Antioxidants neutralise free radicals by donating one of their own electrons while remaining stable, thus helping to protect the body from damage. For example, antioxidants appear to reduce the oxidisability of LDL cholesterol, the type of cholesterol associated with atherosclerosis. Free radicals are also implicated in damaging DNA causing cells to mutate into cancer cells.
There are many types of antioxidants, such as vitamins (eg vitamins C, E), minerals (eg selenium, copper) and a range of non-nutrient compounds (eg carotenoids, bioflavonoids, phenolics). The body produces its own antioxidant compounds, such as superoxide dismutase, catalase and glutathione peroxidase, while benefiting from the additional antioxidants provided in the diet. The ability for antioxidant compounds to protect the body from ill-health seems to work best when antioxidants are provided in the amounts naturally found in a healthy diet rather than through supplementation.
Several large clinical trials using supplements of vitamins C, E and beta-carotene have not shown protection against heart disease. Antioxidant supplements are not recommended by the American Heart Association (http://www.americanheart.org) or the National Heart Foundation in Australia (http://www.heartfoundation.org.au). The studies on antioxidant supplementation and cancer risk have been inconclusive (http://www.cancer.gov/cancertopics/factsheet/prevention/antioxidant s). All major health authorities promote the consumption of a range of fruit and vegetables, including mushrooms.
Antioxidants are abundant in plant foods, from fruits and vegetables to tea, coffee, red wine and cocoa. Although not a plant food, antioxidants are also found in mushrooms. As mushrooms reside in their own biological kingdom, there is great interest in their antioxidant profile as it is likely to differ to that of plant food and therefore have the ability to complement the benefits of antioxidants found in plant foods. One example is ergothioneine, a histidine-based amino acid that functions as an antioxidant. It is abundant in mushrooms, yet found in very few vegetables and none of the fruit.
From the Executive Summary
Antioxidant Activity: Significant antioxidant activities in vitro have been reported in several varieties of mushrooms, with one study reporting antioxidant capacity comparable to vitamin C. The antioxidant activities appear to be related to the polyphenolic content. Of particular interest is that the antioxidant activity (free radical scavenging activity) along with total phenolic and flavonoid concentrations appear to be similar in mushrooms before and after boiling, suggesting that the antioxidant capacity of mushrooms is thermostable (to heating over 100ºC for extended periods of time e.g. 30 min) and in some cases increases during heating suggesting that antioxidant activity would be maintained in cooked mushrooms. L-ergothioneine is a biologically active antioxidant in mushrooms and its production in mushrooms can be enhanced by addition of histidine to the growth medium/compost.
Agaricus bisporus (Savoie et al., 2008), Ganoderma lucidum (Reishi), Phellinus rimosus, Pleurotus florida and Pleurotus pulmonaris (Ajith and Janardhanan, 2007), Volvariella volvacea (Mathew et al., 2008), Thelephora ganbajun, Thelephora aurantiotincta, Boletopsis grisea(Liu et al., 2004a) and others have been reported to have significant antioxidant activities. Of particular interest is that the antioxidant activity (free radical scavenging activity) along with total phenolic and flavonoid concentration of Agaricus bisporus appears to be similar before and after boiling (Jagadish et al., 2009). It has also been suggested that the antioxidant capacities of mushrooms may have a
potentially protective effect against a variety of disease states, including some cancers (Matsuzawa, 2006) and irritable bowel disease (Najafzadeh et al., 2007).
Antioxidant activity via inhibition of lipid peroxidation has been described in several studies. The antioxidant effects of Hypsizygus marmoreus have been studied for peroxyl and alkoxyl radicals by ordinary, non-tumour-bearing and tumour-bearing mice. Oral administration of the fruit body of H. marmoreus exhibited potent anti-tumour or cancer-preventive effects and caused a significant decrease in lipid peroxide levels, which were determined as thiobarbituric acid reactive substances. These results showed that the intake of H. marmoreus fruit body could induce an antioxidant effect, and the increase of antioxidant activity in the plasma of tumour-bearing mice was an important mechanism in cancer prevention. It was also suggested that the mushroom might play a role in the decrease of lipid peroxides through antioxidant activity induction (Matsuzawa, 2006).
Ethanol extracts of the mushroom Phellinus linteus have been shown to have antioxidant activities comparable to vitamin C in scavenging the stable free radical 1,1-diphenyl-2-picrylhyrazyl (DPPH).
The extracts also inhibited lipid peroxidation (LPO) in a concentration-dependent manner. The study also reported anti-angiogenic activities of Phellinus linteus(Song et al., 2003).
A hot water extract from Ganoderma lucidum has been shown to have an antioxidative effect against heart toxicity in mice. Ganoderma lucidum exhibited a dose-dependent antioxidative effect on lipid peroxidation and superoxide scavenging activity in mouse heart homogenate. Furthermore, this result indicated that heart damage induced by ethanol showed a higher malonic dialdehyde level compared with heart homogenate treated with Ganoderma lucidum. The authors concluded that this effect of Ganoderma lucidum may protect the heart from superoxide induced damage (Wong et al., 2004).
A more recent study has examined the effects of an extract of Ganoderma lucidum for its free-radical scavenging property and for effects on liver mitochondrial antioxidant activity in aged BALB/c mice (50 and 250 mg/kg body weight for 15 days) (Cherian et al., 2009). G. lucidum increased antioxidant status in liver mitochondria of aged mice compared with the aged controls. The extract possessed significant 2,2-diphenyl-1-picrylhydrazil (DPPH), 2, 2'-azinobis (3ethylbenzothiazolin-6-sulphonic acid) (ABTS) radical scavenging activities and ferric reducing antioxidant power (FRAP) as well as superoxide and hydroxyl radical scavenging activities.
In vitro evaluation of antioxidant activities of Auricularia auricular has also shown significant inhibition of lipid peroxidation, as well as potent hydroxyl radical scavenging activity when compared to catechin, while crude, boiled and ethanolic extracts were shown to significantly increase nitric oxide (NO) production over the control (Acharya et al., 2004). The natural mushroom pigment Norbadione A and three other pulvinic acids have been shown to display very efficient antioxidant properties in comparison to catechols, flavonoids, stilbenes, or coumarins (Habrant et al., 2009).
Antioxidant activity of submerged cultured mycelium extracts of higher Basidiomycetes mushrooms has recently been reported. Antioxidant properties were studied from 28 submerged cultivated mycelium Basidiomycetes strains of 25 species. Three solvents - ethanol, water (culture liquid),and ethyl acetate were used for extraction. Water extracts from Coprinus comatus, Agaricus nevoi, and Flammulina velutipes showed high antioxidant activities (AA) at 2mg/ml. When the ethanol extracts were tested, the highest AA were found in Agaricus nevoi, Omphalotus olearius, and Auricularia auricula-judae extracts at a concentration of 2mg/ml. The AA of ethanol extracts from Agrocybe aegerita and C. comatus increased from 46.6% to 82.7% and from 2.4% to 62.1%, respectively, when the concentration of the extract increased from 2mg/ml to 4-8mg/ml with the authors suggesting that the extracts could be suitable as antioxidative agents and bioproducts (Asatiani et al., 2007a, Asatiani et al., 2007b).
Antioxidant activities of ten natural p-terphenyl derivatives from the fruiting bodies of three edible mushrooms (Thelephora ganbajun, Thelephora aurantiotincta, Boletopsis grisea) from China have also been reported (Liu et al., 2004b).
In vitro evaluation of antioxidant activities of Auricularia auricular has shown significant inhibition of lipid peroxidation, and potent hydroxyl radical scavenging activity when compared with the drug catechin. The IC50 value of crude, boiled and ethanolic extracts of A. auricula represented 403, 510, and 373 mg/ml respectively of hydroxyl radical scavenging activity and 310, 572 and 398 mg/ml respectively of lipid peroxidation, while crude, boiled and ethanolic extracts were shown to significantly increase nitric oxide production (664, 191 and 850 pmole/mg dry wt/h respectively) over the control (Acharya et al., 2004).
Ganoderma lucidum (Reishi), Phellinus rimosus, Pleurotus florida and Pleurotus pulmonaris have also been reported to have significant antioxidant activities (Ajith and Janardhanan, 2007).
The antioxidative potency of commercially available mushrooms in Taiwan has been studied. The order of inhibitory activity of mushroom extracts on oxidation in an emulsion system was Agaricus bisporus>Hypsizigus marmoreus>Volvariella volvacea>Flammulina velutipes>Pleurotus eryngii>Pleurotus ostreatus>Hericium erinaceus>Lentinula edodes. In a thermal oxidative stability test, using lard, the order of antioxidative activity of the mushroom extracts showed similar tendencies, except for the extract of Lentinula edodes(Fui et al., 2002). Antioxidative activities of Flammulina velutipes extract have also been reported to be able to stabilize the fresh colour of tuna meat during ice storage (Bao et al., 2009).
Heat treatment of Shiitake (Lentinus edodes) significantly increases its antioxidant activity and polyphenolic compounds. The polyphenolic content and antioxidant activities in extracts have been shown to increase as heating temperature and time increased (100 and 121ºC for 15 or 30min). The free polyphenolic content in the extract heated at 121ºC for 30min was increased by 1.9-fold compared to that in the extract from the raw sample. The 2,2-azino-bis-(3-ethylbenzothiazoline-6sulfonic acid) (ABTS) radical and 1,1-diphenyl-2-picrythydrazyl (DPPH) radical scavenging activities were increased by 2.0-fold and 2.2-fold compared to the raw sample, respectively (Choi et al., 2006a). Thermostable antioxidant activity has also been reported from Agaricus blazei Murill (Izawa and Inoue, 2004).
The antioxidant activities of two edible mushrooms (Lentinus edodes and Volvariella volvacea) against lipid peroxidation have been shown to correlate with the phenolic content in different sub-fractions of the mushroom extracts (Cheung and Cheung, 2005). Similarly, significant correlation was found between the total phenolic content from the fruiting bodies of Agrocybe aegerite and antioxidant activity in an ethyl acetate fraction and its sub-fractions (Lo and Cheung, 2005). Extracts of Agaricus blazei, Agrocybe cylindracea, and Boletus edulis have been shown to have significant antioxidant properties with the naturally occurring antioxidant components including total tocopherols (3.18-6.18mg/g) and total phenols (5.67-5.81mg/g) (Tsai et al., 2007).
Antioxidant polyphenols from the mycelial culture of the medicinal fungi Inonotus Xeranticus and Phellinus Linteus have been isolated and identified as hispidin and its dimers, 3,14'-bihispidinyl, hypholomine B, and 1,1-distyrylpyrylethan. These compounds exhibit potent free radical scavenging activity (Jung et al., 2008).
The antioxidant capacity and total phenolic content of Agaricus brasiliensis in two stages of maturity, young (YB) and mature (MB), have been evaluated with minor differences in the composition of phenolic compounds being detected, but with similar antioxidant activities, except for the chelating ability for ferrous ions, which was higher in MB than in YB (Soares et al., 2009).
Total phenols have been shown to be the major antioxidant components in ethanolic extracts in a variety of culinary and medicinal mushrooms (Tsai et al., 2008, Tsai et al., 2009). The antioxidant properties in mushrooms decrease significantly with storage time, with recommendations being made that mushrooms be stored at 4ºC for up to 6 days (Tsai et al., 2008). DPPH (1,1-diphenyl-2picrylhydrazyl) activities have also been shown to significantly correlate with total content of phenolic compounds in a variety of edible and medicinal mushrooms (Kim et al., 2008).
Ergothioneine is a native membrane-impermeable thiol compound that is specifically accumulated in cells via the organic cation transporter OCTN1. In humans, OCTN1 and ergothioneine have been implicated in the etiopathogenesis of autoimmune disorders. Few foods contain ergothioneine, with highest concentrations detected in specialty mushrooms, kidney, liver, black and red beans, and oat bran. Ergothioneine has been reported to exhibit cell protection only against copper(II)-induced toxicity but is far less potent than glutathione, indicting that ergothioneine is not involved in the intracellular antioxidant thiol defence system (Ey et al., 2007).
L-ergothioneine is a biologically active antioxidant produced by certain fungal species and mycobacterium. The precursors to the synthesis of L-ergothioneine are the amino acids histidine, cysteine, and methionine. Supplementation with L-ergothioneine has been shown to have a protective effect on the organs of rats against lipid peroxidation and to conserve the consumption of endogenous glutathione and alpha-tocopherol (Deiana et al., 2004).
The ergothioneine content of mushrooms has been reported to be in the range of 0.4-2.0mg/g (dry weight). White Agaricus bisporus contained the least ergothioneine and portabellas (brown) contained the highest within the varieties of A. bisporus studied. The specialty mushrooms tested (Lentinus edodes, Pleurotus ostreatus, P. eryngii, Grifola frondosa) all contained a statistically significant greater amount of ergothioneine compared to A. bisporus; however, no significant difference was found between the specialty mushrooms studied (Dubost et al., 2006).
An ergothioneine derivative, b-hydroxyergothioneine has been isolated from the mushroom Lyophyllum connatum. Ergothioneine,N-hydroxy-N',N'-dimethylurea, and connatin (N-hydroxyN',N'-dimethylcitrulline) were also isolated. All the compounds displayed the ability to scavenge free radicals, based on a 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay. The radical scavenging activity of b -hydroxyergothioneine was very similar to that of ergothioneine. b-Hydroxyergothioneine showed the greatest protective activity against carbon tetrachloride-induced injury in primary culture hepatocytes (Kimura et al., 2005).
Protein supplement treatments during mushroom growth do not have a significant effect on the amount of L-ergothioneine produced by mushrooms, but the addition of histidine to compost has been reported to significantly increase the amount of L-ergothioneine. Furthermore, Lergothioneine was increased by up to 1.3mg/g dry weight in later flushes by several stress factors placed on the mycelia, such as dry compost, indicating that L-ergothioneine may be a stress factor. A postharvest shelf-life study has also demonstrated that L-ergothioneine significantly decreased during postharvest storage for up to 6 days at 12ºC (Dubost et al., 2007).