## 3 Results
### Fibre Content and Composition  
As can be observed in Table 1, fiber was the main component of the mushroom DFI for all the conditions employed and ranged from 45.9% to 70.4%. Only the factor \(T\) had a significant negative effect on the DFI fiber content (Table 2), therefore although higher treatment times resulted in higher DFI yields, there was also observed a decrease in the relative abundance of dietary fiber in the DFL. The previously described increase in the DFI yield with \(T\) is not related to an increase in fiber retention during the treatment as there was not observed a correlation between fiber yield and treatment time (R  
Figure 1: Response surfaces for mushroom DFI yield as a function of: (**a**) time and hydrogen peroxide concentration (at sodium hydroxide concentration level of 1.682); (**b**) time and sodium hydroxide concentration (at hydrogen peroxide concentration level of 1); (**c**) hydrogen peroxide concentration and sodium hydroxide concentration (at time level of 1.682). = 0.2092). For obtaining a mushroom DFI with higher fiber contents the lower processing times assure this value (Table 1). The yield of dietary fiber obtained ranged between 0.50% of the mushroom's fresh weight to 1.3%, corresponding to a yield of fiber between 31% and 81% of original mushroom fiber content (on average 54%). This yield is explained by the fact that some of the _A. bisporus_ polysaccharides are water and alkali-soluble [48]. In Table 3 it is shown the sugar composition of the mushroom DFI obtained for the different experimental conditions tested. In addition, the sugar composition of the fiber of the freeze-dried mushrooms is shown. The method applied resulted in a relative increase of the fiber in the DFI from 1.9 to 2.9 times in comparison with the original mushroom, showing the efficiency of the method employed for enriching the DFI with the original mushroom fiber. As can be observed, the main sugars present in the mushroom DFI were glucose followed by glucosamine and xylose that together account for more than 91% of the total sugars present. Smaller amounts of mannose, glucuronic acid, fucose, and galacturonic acid were also present. This sugar composition is similar to that described in previous works that have shown that _A. bisporus_ cell walls are composed predominantly by \(\beta\)(1\(\rightarrow\)3)-linked glucan containing some \(\beta\)(1\(\rightarrow\)6) linkages containing also chitin [27; 48; 49]. FTIR analysis of the DFI confirms the presence of chitin (Figure 2). The spectra had characteristic bands at 3400-3480 cm\({}^{-1}\) that responded to OH-3 and CH\({}_{2}\)OH-6 intra- and intermolecular hydrogen bonds, bands at 1650 cm\({}^{-1}\) for amide I, and 1557 cm\({}^{-1}\) for amide II vibrational mode. The chitin present in the mushroom DFI is in an antiparallel \(\alpha\)-conformation [50] as there is observed a split of the amide I vibration band at 1655 cm\({}^{-1}\), identical to the reference crustacean chitin (Figure 2). These results confirmed that the glycosaminoglycans of DFI from _A. bisporus_ were in highly acetylated form. The ratio of intensities of the bands at \(\sim\)1379 and \(\sim\)2920 cm\({}^{-1}\) has been suggested as the crystallinity index for chitin and chitosan [51]. The crystallinity index of the DFI chitin was similar to that of the reference chitin (1.07 vs. 1.12, respectively) and higher than that observed for the reference chitosan (0.78). The crystallinity index obtained mushroom DFI was higher than that obtained by [PERSON] et al. [27], this being probably due to the preparation method used by these authors (1M NaOH at 95 \({}^{\circ}\)C during 30 min followed by 2% acetic acid at 95 \({}^{\circ}\)C during 6 h). A clear spectrum of the glucan in DFI could not be observed, due to the overlapping of chitin bands and the lack of unique bands in \(\beta\)-glucans when compared to chitin (Figure 3).