## 3 Results and Discussion
### Antioxidant Power (FRAP, ABTS and SRSA Assays)  
The antioxidant capacity of the liquors was assessed based on three assays (Table 3). In general, for all the applied assays, it was confirmed that for the total phenols, there was a higher release of antioxidant compounds with the auto-hydrolysis process, by almost 5 times for the FRAP and Superoxide test, and more than 20 times for the ABTS test. In the literature ([PERSON] et al., 2017), it is generally observed a high correlation between this kind of tests and the Folin assay, since, as already explained, the Folin also measures the antioxidant capacity (as reducing power) of a sample. Evaluation of the specific antioxidant power showed a high correlation in the case of the FRAP and Superoxide assays, since the calculated values were comparable for the two liquors, while the ABTS test showed a higher specific antioxidant capacity for the phenolic compounds contained in the auto-hydrolysis liquor. Concerning acid hydrolysis, the antioxidant power obtained reflects the trend assessed by [PERSON] et al. [14], who studied the antioxidant activity of dilute acid hydrolysate of wheat straw. Moreover, FRAP and ABTS and also Folin assays confirm that wheat straw, a raw material with high content of cellulose and lignin, releases less antioxidant compounds compared to other biomasses, such as fruit pomace, and so is more suitable for cellulose recovery [55; 56]. Indeed, FRAP and Folin assay test values are about 160 times and 120 times lower, respectively, than those reported by [PERSON] et al. [35], who analyzed the antioxidant recovery from grape pomace using auto-hydrolysis process in similar operating conditions. On the other hand, [PERSON] et al. [57] analyzed the liquors obtained from the auto-hydrolysis at different operating temperatures of vine shoots, that are a more  
\begin{table}
\begin{tabular}{l c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multicolumn{2}{c}{**Auto-Hydrolysis**} & \multicolumn{2}{c}{**Acid Hydrolysis**} \\ \cline{2-5}  & **mg/L** & **mg/g\({}_{\text{dm}}\)ws** & **mg/L** & **mg/g\({}_{\text{dm}}\)ws** \\ \hline
**Total phenols (Folin\_GAE)** & 1532.28 \(\pm\) 61.56 & 20.06 \(\pm\) 0.77 & 1211.86 \(\pm\) 71.66 & 4.70 \(\pm\) 0.29 \\
**Total phenols (280\_GAE)** & 4990.78 \(\pm\) 401.01 & 65.32 \(\pm\) 5.12 & 6932.85 \(\pm\) 240.63 & 27.24 \(\pm\) 0.95 \\
**Cinnamic acids (FAE)** & 137.91 \(\pm\) 52.42 & 1.81 \(\pm\) 0.69 & 41.64 \(\pm\) 11.49 & 0.16 \(\pm\) 0.05 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Total phenols and cinnamic acids content of wheat straw (WS) auto-hydrolysate and acid hydrolysate liquors. GAE: gallic acid equivalents. FAE: ferulic acid equivalents. Values are reported as mean values (\(n=3\)) \(\pm\) sd.  
lignocellulos biomass. [PERSON] et al. obtained 12.2 mgGAE/gvine shoot of total phenol content which is similar to the value obtained for wheat straw extracts. Another example is the spent coffee grounds, that are expected to release a low amount of antioxidant compounds due to a previous extraction with hot water during coffee preparation. [PERSON] et al. [58] tested different auto-hydrolysis conditions to optimize the process for antioxidant compounds recovery from spent coffee grounds, finding values of about 25 mg GAE/g, similar to the one obtained in this work for wheat straw.