## 3 Results and Discussion
### Functional Properties of Mushroom Powder, Wheat Flour, and Blended Flours
ostreatus_ powders had higher oil-holding capacity (548.3% and 462.6% respectively) compared with maize flour (297.2%), and replacing the base flour with mushroom powders by 10% up to 50% resulted in an increase in fat binding in composite flours (from 302.2% to 433.2%). The OHC is an important feature that can improve flavor and mouthfeel and enhance texture and product yield [96]. The main ingredients that contribute to fat-holding capacity are hydrophobic proteins [97]. Thermal processing of food leads to the exposure of a larger amount of non-polar amino acids in the protein side chains, which in turn results in a stronger bond of proteins with fats [98]. These protein-lipid interactions are attributed to the physical binding of fat molecules between proteins and non-covalent bonds, including hydrophobic, hydrogen, and electrostatic bonds [99]. OHC is particularly desirable in products with minced meat, in meat substitutes, graves, and soups, and allows the storage time of bakery and confectionery products to be extended [96]. The swelling capacity (SC) describes the ability of the matrix to expand due to water absorption [95]. Data regarding swelling capacity (SC) are presented in Table 5. Higher values for the discussed parameter were found for freeze-dried _A. bisporus_ (20.51 mL/g) and _P. ostreatus_ (16.51 mL/g), while the SC for wheat flour was 2.59 mL/g. However, significantly (\(p<0.05\)) higher SC values of blended flours were recorded only for the versions in which the base flour was replaced by 6% mushroom powder. According to [PERSON] et al. [17], SC for mushroom powder is 14.47 mL/g and 13.71 mL/g for button and oyster mushrooms, respectively. In turn, the SC for composite flours where 10 to 50% of maize flour was replaced with mushroom powder ranged from 12.3 mL/g to 12.97 mL/g, while the SC for 100% maize flour was 12.81 mL/g. The results presented in the next paper [95] show that the SC of freeze-dried _A. bisporus_ depends on the practical size of the mushroom powder. The data show that coarse mushroom powder has a significantly (\(p<0.05\)) higher SC (10.92 mL/g) compared with fine (SC = 8.20 mL/g) and superfine (SC = 3.13 mL/g) mushroom powders. The SC of flour is influenced by the amounts of proteins, starch, and fiber [100]. [PERSON] et al. [17] suggest that hydrating properties, including WHC and SC, are probably caused by the presence of fiber and a porous structure favoring the absorption, retention, and swelling of flour particles in water. This is confirmed by our research showing that mushroom powders have higher content of these compounds than wheat flour (Table 1). The results of the WSI measurements of the samples are presented in Table 5. This parameter was higher for mushroom powders (42.13% for _A. bisporus_ and 54.06% for P. ostreatus) compared with wheat flour (7.30%). For composite flours, WSI was significantly (\(p<0.05\)) higher for flours with 4% or 6% addition of mushroom lyophilistes compared with the WSI of base flour, and the highest value for this parameter was recorded for blended flour with 6% addition of oyster mushrooms (11.15%). Determining the WSI values of mushroom powders and composite flours with the addition of mushrooms has been the subject of research by other authors. [PERSON] et al. [17] reported that the solubility index of button mushroom flour was 60.25% and that for oyster mushroom flour was 50.99%, and the WSI for mushroom-enriched flours increased with the increase in the amount of mushroom powder. Another work reported the solubility index values for mushroom powders to be 26.55 g/g, 5.26 g/g, and 8.39 g/g for _Lentiumal codes_, black, and silver ear mushrooms, respectively [71]. The presence of proteins and soluble dietary fiber is largely responsible for the hydrating properties of mushrooms, and a higher amount of these compounds results in a higher solubility index [101]. Mushrooms are an abundant source of complex carbohydrates, including chitin and the water-soluble polysaccharide fraction (WSP).