Mushrooms are the second largest edible biomass available from Finnish forests. Their main components are non-digestible polysaccharides such as β-glucans, mannans, and galactans. These molecules have been shown to possess a large variety of biological activities. These activities are determined by their
physicochemical properties, like sugar composition, glycosidic linkage and molecular weight, which are significantly influenced by the fungal species and extraction methods. Currently, the low collection of natural basidiomycete production leaves the edible mushroom biomass largely unused. Development of β-glucan-oriented isolation and purification schemes can increase the value of Finnish mushrooms, meeting the rapidly growing international market for functional foods and nutraceuticals.
Usually, β-glucans are extracted from fungi with hot water. Higher yield and purity of these molecules can be achieved by pre-treatments and harsher extracting conditions. For a complete understanding of influence of processing parameters on composition and properties of polysaccharides, thorough characterization of molecular properties of the obtained polysaccharides is also required. Seasonal variation, slow growth and logistic problems might hamper the mushroom industry. Currently, two strategies are studied to overcome these issues: cultivation of fungal mycelium in liquid medium (submerged cultivation) or on solid substrate (solid-state cultivation). The produced biomasses can be readily used as source of fungal polysaccharides. Submerged cultivation is further favored by low cost and fast production. Moreover, the use of lignocellulosic, such as agricultural sidestreams, and liquid, such as oils, supplements to the medium has been shown to increase mycelial yield.
The aim of the current work was to extract polysaccharides from Finnish fungal resource and determine their yield and properties utilizing colorimetric, chromatographic, and spectroscopic techniques. The cultivated Agaricus bisporus, wild Craterellus tubaeformis, and rare and slow-growing Inonotus obliquus were investigated as polysaccharide resource. The effects of a pretreatment with ethanol-hydrochloric acid mixture, prior to sequential hot water extractions, were investigated using A. bisporus. Cell wall polysaccharides were extracted from C. tubaeformis with a sequential protocol of increasing harshness using hot water and alkaline solutions of different concentrat. Cultivated mycelium of I. obliquus was considered as an alternative of the sterile conk, commonly known as Chaga, produced by this species as polysaccharide source. Sea buckthorn (Hippophaë rhamnoides) berry press cake, a fibrous side stream with high oil content, was supplemented to the submerged cultivation medium of I. obliquus. Exopolysaccharides (EPS) from culture media and intracellular polysaccharides (IPS) extracted from mycelia were investigated. Moreover, the potential of the birch heart rot, resulted from infection by this species, as polysaccharide source has been assessed in this work for the first time. Polysaccharides from wild sterile conk, cultivated mycelium, and heart rot were extracted, characterized, and compared.
The pretreatment with acid and the use of alkali during the extraction resulted in disruption of the cell wall, which facilitated the solvent access to its deeper layers. The harsher methods increased extraction yields and the β-glucan contents in the extracts, while decreasing the molecular weight of the polysaccharides. In case of C. tubaeformis, hot water was an inefficient extraction medium for β-glucans. Structural investigation assigned to these polymers a backbone of →6)-β-Glc-(1→ units with short and frequent branches in O-3 position. The thermal stability of fungal polysaccharides was drastically reduced only after strong alkali extraction. Supplementation with press cake increased the cultivation yield of I. obliquus. The  supplementation positively affected the yield and molecular weight of EPS. However, at higher dosages, the
supplementation reduced content and the molecular weight of IPS. The pectins in the sea buckthorn press cake affected to small extent the monomer composition of both IPS and EPS. The polysaccharides extracted from cultivated mycelium showed high abundance of glycogen, absence of phenolic compounds, and polydispersed polymer populations, while the opposite was observed for sterile conk polysaccharides. Structurally similar β-glucan was identified in sterile conk and mycelium extracts. On the other hand, heart rot polysaccharides were mainly composed of hemicelluloses. However, fungal polysaccharides were identified as well, particularly in the hot water extract, showing potential also for the birch leftover after sterile conk harvesting. The results of the present doctoral thesis offer valuable information for the
exploitation of Finnish fungal species as sources of bioactive polysaccharide (in particular β-glucan) aimed to the nutraceutical market. Moreover, this thesis could be a starting point for more in-depth studies on the effect of liquid culture supplementation on the macromolecular properties of mycelial polysaccharides.