# Bivolarization of Grape Stalks as Animal Feed by Solid State Fermentation Using White-Rot Fungi
## 3 Results and Discussion
edodes_, the delignification process was positively related to the incubation period, decreasing lignin content by \(-33\), \(-45\) and \(-52\%\) after 28, 35 and 42 days of incubation, respectively. Based on these results it is possible that a longer incubation period could enhance a higher delignification of cell wall contents, since the values have not reached a plateau. Similar results in delignification were found by [PERSON] et al. [40] when inoculating oil palm fronds with _L. edodes_. In fact, it was observed that there was a decrease in the lignin content of this substrate by \(-30\) and \(-58\%\) after 21 and 63 days of incubation, respectively. By contrast, the treatment with _P. eryngii_ only showed a decrease of 5% of the lignin content of GS, even after 42 days of incubation. [PERSON] et al. [43] also observed a small delignification (\(-15\%\)) ability of _P. eryngii_ on sugarcane bagasse after a longer incubation period (155 days). \begin{table}
\begin{tabular}{l c c c c c c c c c c c} \hline
**IP** & **Fungi** & **DM** & **Ash** & **CP** & **NDFom** & **ADFom** & **HC** & **Cel** & **Lignin(sa)** & **HC/L** & **Cel/L** & **IVOMD** \\ \hline \multirow{4}{*}{28} & Control & 31.5 \({}^{\text{a}}\) & 5.6 \({}^{\text{t}}\) & 4.8 \({}^{\text{d}}\) & 68.3 \({}^{\text{cd}}\) & 62.1 \({}^{\text{abc}}\) & 7.02 \({}^{\text{cd}}\) & 27.9 \({}^{\text{c}}\) & 33.7 \({}^{\text{ab}}\) & 0.21 \({}^{\text{ef}}\) & 0  
According to [PERSON] et al. [16], the ratio of structural carbohydrates/lignin is an important measure to evaluate the selectivity of fungi to degrade lignin and, at the same time, retain the structural carbohydrates. In non-selective fungi, delignification is associated with important structural carbohydrates losses. These structural carbohydrate losses represent a disadvantage when the objective is the valorization of different substrates for animal production, since these structural carbohydrates could be used as an energy source by the animals. During the incubation period of GS, the ratio of hemicellulose/lignin (Table 1) increased from 0.21 (control) to an average of 0.35 (_P. citrinopileatus_) and 0.60 (_L. edodes_) at 42 days of incubation. For the ratio of cellulose/lignin, an increase (_p_ < 0.001) in its value was only observed in the GS treated with _L. edodes_, increasing from 0.84 (control) to 2.00 at the same incubation time (Table 1). These results (Figure 2) indicated that _L. edodes_ showed a higher selectivity for the delignification of GS when compared to the consumption of the structural carbohydrates. In fact, other authors [40; 44] reported that _L. edodes_ is a potential fungal species for the treatment of different raw materials with high lignin content. [PERSON] et al. [40] studied the effects of the incubation of ten WRFs on oil palm froms and determined the relative selectivity for lignin degradation according to the equation proposed by [PERSON] et al. [45]. After comparing the results between the WRF, these authors observed that _L. edodes_ presented a higher relative selectivity for lignin degradation (Srel = 0.98). [PERSON] et al. [44] compared the selective delignification of wheat straw by three WRF (_C. subvernispora_, _P. eryngii_, and _L. edodes_) across the quantification of initial and final lignin content. These authors observed that _C. subvernispora_ and _L. edodes_ outperformed _P. eryngii_ in terms of the extent and selectivity of delignification. As a consequence of the abovementioned modifications in the cell wall contents, IVOMD was altered (_p_ < 0.001) by the fungal treatments. The data clearly showed differences in the fungal degradation activity, indicating higher IVOMD values of GS treated with _L. edodes_ (496 g/kg OM) and _P. citrinopileatus_ (344 g/kg OM) when compared to the control (289 g/kg OM), with _L. edodes_ being the most effective fungi-enhancing IVOMD. In fact, for _L. edodes_, a constant increase of IVOMD was observed across all incubation periods, varying between 32, 55, and 72% for incubation times of 28, 35, and 42 days, respectively.