## 4 Bioactive Metabolites
### Fatty Acids and Lipids  
All fatty acids have important roles in the human body, and thus human diet must include foods containing fatty acids [134]. Macrofungi contain a wide variety of fatty acids, but the biggest percentage are polyunsaturated fatty acids (PUFA) and specifically linoleic acid, which is an important essential \(\omega\)-6 fatty acid that cannot be synthesized in the body [135]. The PUFA contents of mushrooms are greater than those found in cattle and pork while containing low amounts of saturated fatty acids (SFA) [135]. PUFAs have been shown to reduce serum cholesterol [73] and play an important role in the regulation of cell physiology and cardiovascular health [136]. The fatty acids found in _P. ostreatus_ were 28 in total, but linoleic acid was in the highest concentration (57-81%), followed by oleic (6-20%), and palmitic acid (8-12%) [91]. Agitated submerged cultures of _G. applanatum_, _M. esculenta_, _A. aegypti_, and _P. pulmonarius_ produced significant quantities of unsaturated fatty acids [96]. Agitation of the shake flasks has been reported to have a positive impact on lipid biosynthesis by macrofungi [137]. _Tuber aestivum_ cultivated in liquid cultures containing rice cereal hydrolyostas as the sole carbon source produced the highest amount of lipids compared to _M. vulgaris_, _M. elata_ _L. edodes_, and _A. bisporus_ in substrates of agroindustrial waste [25]. _Volvariella volvacea_ biomass produced in synthetic media contained 0.7 g/L of total lipids with linoleic acid being predominant. The researchers report that lipid synthesis was independent of the C/N ratio and that the considerable amounts of lipids (32% \(w/w\)) synthesized early in the culture started decreasing after the 8 th day until they reached 3% by the end of cultivation. Fractionation of the produced lipids revealed that most of the lipids produced were neutral (65% \(w/w\)), followed by glycolipids and sphingolipids (30% \(w/w\)), and phospholipids in negligible amounts (2-3% \(w/w\)). The composition of fatty acids was not significantly influenced by the different C/N ratios, contrary to that of neutral lipids which increased in the high C/N ratio substrate [23].  
The major sterol found in macrofungi is ergosterol, which is a well-known steroid precursor of vitamin D2 and a fundamental molecule for many biological processes. When commonly consumed mushrooms such as _P. ostreatus_, _A. bisporus_, and _L. edodes_ are exposed to UV radiation for a short time (1-3 s), ergosterol is transformed into vitamin D2 in nutritionally relevant amounts [138]. Ergosterol has also been linked with preventive action against cardiovascular diseases and antioxidant properties[70]. Cultivation of macrofungi on agri-food residues produced fruiting bodies with enhanced quantities of ergosterol (11-26 mg/g) [106]. _P. citrinopiletatus_ cultivated on grape marc plus wheat straw produced significant quantities of ergosterol (5.53 mg/g dw) [139]. Other polyunsaturated fatty acids found in mushrooms, tocopherols, are natural antioxidants with high biological activity against degenerative malfunctions, and microbial and cardiovascular diseases [124]. Ceramides are waxy lipids composed of sphingosine, a fatty acid with application in foods and cosmetics. Novel ceramides have been isolated from _G. fondosa_ and _Armillaria_mellea_[88]. The lipids produced by macrofungi could also be utilized in the development of healthier and more sustainable food products [140]. It should be added that the fatty acids and their metabolic products are partially responsible for the characteristic unami aroma and flavor compounds of mushrooms [141].