## 4 Discussion  
Similar approaches of irradiating fresh living fungi or plants, in order to enhance their nutritional value, showed similar results, depending on the experimental design and the assessed compounds. Working with _Cordyceps militaris_ medicinal fungus and using UV-B as source of radiation, [PERSON] et al. [29] showed that the flavonoid content increased by  
Figure 3: The effect of gamma irradiation and response-time after treatment on the total flavonoids content in methanolic extract of _Fomes fometarius_ mycelium. Results are expressed in quercetin equivalent as average irradiated/untreated control ratio (\(n=120\) per time). Bars are one standard deviation (SD). 30.6 to 56% in living mycelium (depending on the preparation method) and by 10.4% in living fruiting bodies. UV-B irradiation also considerably increased total phenol content in mycelia, but had insignificant effect on mushrooms. However, we must notice that time after irradiation, up to the freezing step, is not mentioned and, according to our estimation, the absorbed energy (in Joules) was ~11 times higher in UV-B irradiated _Cordycps_ than in our experiment (gamma irradiated _Fomes fomentarius_ mycelium). [PERSON] et al. (2014) [30] found that acute gamma irradiation enriches the content of some polyphenols and flavonoids in _Curcuma alismatifolia_ leaves of plants whose rhizomes have been previously irradiated. All analyzed polyphenols, namely salicylic acid, caffeic acid, catechin, epicatechin, cinnamic acid, ellagic acid, resorcinol and flavonoids, namely rutin, naringin, apigenin, quercetin, myricetin, showed an increase in a range similar to our work. Their experiment was performed at doses of about an order of magnitude smaller than ours (tens of grays), since plants are less radioresistant than fungi and their highest dose (20 Gy) presented the highest increase in both polyphenols and flavonoids. [PERSON] et al. [31] also found that irradiation with UV-B light after harvest enhanced the amount of flavonoids, phenols and total phenols in tomato fruits, while [PERSON] et al., [32] reported that low-dose UV-B light treatment to freshly cut carrot products could increase the total soluble phenolic content and enhance antioxidant activity. The penetration power of the two radiation sources is, however, different: while ultraviolet radiation acts only on the surface, gamma photons are highly penetrating, making results only partially comparable. [PERSON] et al. [33] showed that the enzymatic (superoxide dismutase, SOD and total peroxididases, POD) and non-enzymatic antioxidant activity (total phenolic) increased significantly in _Deschampsia antarctica_ plants in hydroponic system, in response to UV-B treatment. A peak in total phenolic content of _D. antarctica_ was found at 3 h of exposure, which related to percentage of consumed DPPH and FRAP values, suggesting that these phenolics function as soluble antioxidant metabolites. Various polyphenols have antioxidant and anti-inflammatory properties that could have preventive and/or therapeutic effects for cardiovascular disease, neurodegenerative disorders, cancer, and obesity [34]. Submerged fermentation is a method at hand for producing fungal biomass of rare and/or slow growing species. The process is easily controllable, regardless of the season, and the total and specific compound yield are predictable. Mycelia and/or fermentation broth could be harvest in couple of days to few weeks, depending on the desired metabolite. Freeze-drying of live mycelium is a good method to both conserve the properties of compounds and to catch the differences between treatments and response time, since metabolic activity is completely interrupted. Our experimental approach reveals gamma irradiation as a novel biotechnological tool to obtain medicinal mycelium with improved antioxidant properties. Such a natural resource is highly desirable for pharmaceutical, as well as for nutraceutical products.