# Bivolarization of Grape Stalks as Animal Feed by Solid State Fermentation Using White-Rot Fungi
## 3 Results and Discussion  
The chemical composition and _in vitro_ organic matter digestibility (IVOMD) of the treated and untreated (control) grape stalks (GS) are presented in Table 1. Results showed an effect (\(p<\) 0.001) of the white-rot fungi (WRF) treatment on all chemical parameters. Data indicated a decrease of the DM content of GS treated with the WRF when compared with the control (\(p<\) 0.05), except for _P. eryngini_ at 35 and 42 days, probably due to the observed decrease of activity of the mycelium on the substrate for these periods. Regarding ash content, an increase was observed for all GS treated with the WRF when compared with the control (\(p<\) 0.05). Ash content for _P. eryngini, L. edodes_ and _P. citrinopileatus_ showed an average increase of 22%, 47%, and 68%, respectively. This increase in ash was also reported by other authors when inoculating different substrates with WRF [34; 35]. The data indicated a higher CP content of GS treated with the WRF when compared with the control (\(p<\) 0.05), showing increases of 32, 78, and 106% for _P. eryngini, L. edodes_, and _P. citrinopileatus_, and at 42 days of incubation, respectively. These data are consistent with results presented in other studies [16; 25; 36; 37; 38]. One possible explanation for this increase could be related to the analytical method used for N quantification. The Kjeldahl N method does not quantify all forms of inorganic nitrogen (e.g., nitrates and nitrites; [38]) and fungi are known to possess nitrate and nitrite reductases, allowing them to convert these inorganic forms of nitrogen into quantifiable Kjeldahl N method-measurable ammonia [39], thus contributing to an increase in the total N measurements after incubation. Data showed that the WRF treatment promoted changes (\(p<\) 0.001) in the GS cell wall components. A decrease in NDFOm and ADFOm contents was observed on treated GS with _L. edodes_ when comparedwith the control (\(p<0.05\)), with a decrease of 14 and 20% at 42 days of the incubation period, respectively. Similar results were also reported in other studies [22; 35; 40; 41; 42] when incubating _L. edodes_ with other raw materials. In fact, [PERSON] et al. [22] found a decrease of 30 and 18% in NDF and ADF contents, respectively, after 49 days of incubation of wheat straw with _L. edodes_. [PERSON] et al., [40] also observed a decrease of 15 and 20% in NDF and ADF content, respectively, after 63 days of incubation of oil palm fronds treated with _L. edodes_. In contrast, when treating GS with _P. eryngii_, an increase in the NDFom content was observed, with an average 6% when compared to the control. These results could be linked to the low biodegradation of cell wall components performed by _P. eryngii_ on GS when compared with the other used fungi. [PERSON] et al. [42] studied the effects of different WRF (_Ceriporiopsis subvernispora_, _L. edodes_, _P. eryngii_, and _P. ostreatus_) on different raw materials (maize stover, rice straw, oil palm fronds, and sugarcane bagasse) with an incubation time of 42 days and they reported lowest losses in the cell wall contents of the raw materials when using _P. eryngii_. In addition, it should also be stated that another reason for this increase might also be due to the proportionally higher hydrolysis potential of soluble components when compared to the degradation of cell wall components. The modifications observed in the NDFom and ADFom fractions can be the result of the WRF activity on the three-dimensional structure of the cell wall, enhancing both the degradation of structural carbohydrates (hemicellulose and cellulose) and the solubilization of lignin. The results herein presented for the cell wall components were mainly due to the delignification of the cell wall instigated by the WRF. In fact, the incubation of GS with _P. citrinopilatus_ and _L. edodes_ resulted in a decrease of \(-17\) and \(-43\%\) of lignin content, respectively. In the case of _L.