## 3 Results and Discussion
### Fungal Colonization of Solid Substrates and Impact on Their Chemical Composition
Although not experimentally demonstrated, the acidification observed in solid-state cultures was presumably due to the production of organic acids, a general metabolic characteristic among the species belonging to the _Aspergillus_ genus that can lead to the substrate pH being lowered by four units [14; 48; 49]. The production of organic acids by these species seems to be a strategy implemented in nature to counteract the antagonistic effect exerted by bacteria [50]. Conversely, on the DSF, the solid-state cultures' pH values were higher than those of the incubation controls, albeit with limited variations. The lack of acidification on this matrix may be due to the known buffering capacity of the digestate [51]. Table 2 also shows the biotic losses of organic matter are attributable to mineralization and calculated based on the ash contents of the solid-phase cultures and the related \begin{table}
\begin{tabular}{c c c c c c} \hline
**Solid-State** & **D-Glucosamine** & **EXP (mg g\({}^{-1}\))** & **\(\Delta\)pH \(\uparrow\)** & **OML \(\downarrow\) (\%)** & **YGLCS (mg g\({}^{-1}\))** \\ \hline RTB & 0.87 \(\pm\) 0.05 ab & 2.89 \(\pm\) 0.24 b & \(-\)0.80 (6.93 \(\pm\) 0.03) & 12.64 \(\pm\) 0.40 c & 6.88 \(\pm\) 0.50 b \\ RTB + WB & 1.89 \(\pm\) 0.07 c & 3.49 \(\pm\) 0.11 c & \(-\)0.56 (6.43 \(\pm\) 0.04) & 17.01 \(\pm\) 0.60 e & 11.11 \(\pm\) 0.41 c \\ SCG & 0.94 \(\pm\) 0.06 b & 2.00 \(\pm\) 0.09 a & \(-\)1.75 (5.77 \(\pm\) 0.04) & 10.77 \(\pm\) 1.21 b & 8.73 \(\pm\) 0.46 b \\ SCG + WB & 2.47 \(\pm\) 0.08 d & 1.89 \(\pm\) 0.12 a & \(-\)0.73 (5.34 \(\pm\) 0.02) & 14.70 \(\pm\) 0.81 d & 16.80 \(\pm\) 0.54 d \\ BS & 0.70 \(\pm\) 0.06 a & 5.46 \(\pm\) 0.33 d & n.s. * (6.50 \(\pm\) 0.04) & 8.43 \(\pm\) 0.34 a & 8.30 \(\pm\) 1.30 b \\ BS + WB & 2.99 \(\pm\) 0.21 e & 5.04 \(\pm\) 0.18 d & \(-\)0.17 (6.83 \(\pm\) 0.02) & 12.24 \(\pm\) 0.78 bc & 24.44 \(\pm\) 1.63 e \\ DSF & 0.79 \(\pm\) 0.04 ab & 3.68 \(\pm\) 0.07 c & \(+\)0.24 (6.60 \(\pm\) 0.05) & 17.73 \(\pm\) 0.51 e & 4.46 \(\pm\) 0.49 a \\ DSF + WB & 0.87 \(\pm\) 0.03 ab & 3.70 \(\pm\) 0.38 c & \(+\)0.64 (6.92 \(\pm\) 0.08) & 17.03 \(\pm\) 0.46 e & 5.11 \(\pm\) 0.7 ab \\ \hline \end{tabular} (+) The data in round brackets are the pH values found in the non-inoculated incubation controls; (+) calculated from the ash content in solid-state cultures and related incubation controls using the equation of [PERSON] et al. (2002); * n. s., not significant (pH values of solid-state cultures did not significantly differ from the respective incubation controls).  
\end{table} 
Table 2: D-glucosamine and extracellular protein (EXP) contents, pH changes, organic matter losses (OML) and yield of fungal biomass per unit of organic matter consumed (Y\({}_{\text{GLC/S}}\)) in 14-day-old _A. olivimuriae_ solid-state cultures carried out on residual thistle biomass (RTB), spent coffee grounds (SCG), barley straw (BS) and solid fraction of digestate (SFD) in the presence and in the absence of wheat bran (WB). Data are mean \(\pm\) standard deviation of 4 replicates. Multiple pair-wise comparisons were made with [PERSON]’s test, and identical letters denote that column means were not statistically different (\(p\) > 0.05). incubation controls. The amendment's presence increased the extents of organic matter losses in thistle biomass, barley straw and SCG. Conversely, this parameter's values did not significantly differ in non-amended and amended cultures on DSF (17.73 \(\pm\) 0.51 and 17.03 \(\pm\) 0.46, respectively). The values of the biomass yields (Y\({}_{\text{GLC/S}}\)), derived by relating D-glucosamine levels to the unit mass of organic matter consumed, did not significantly differ in non-supplemented cultures, while the presence of the WB markedly increased this parameter in amended ones. Table 3 shows the contents in cellulose, hemicellulose, lignin, reducing sugars, crude lipids and total phenols in the incubation controls and the respective cultures inoculated with _A. olivimuriae_.