# Valorization of Cassava By-Products: Cyanide Content and Quality Characteristics of Leaves and Peel
## 3 Results and Discussion
### Changes in Composition, Fiber, and Cyanide Content of Cassava Tuber Peel after Enzymatic Treatment  
In Figure 4, the compositional analysis of cassava tuber peel reveals some changes after treatment with hot water and Viscozyme(r) L solution. Dry matter and organic matter were higher in the fresh peel (FP) and the enzyme-treated peel (ETP1-3) than in the control peel (CP) treated with hot water without enzyme solution. However, the ash content in the CP was high, which can be directly attributed to the low organic matter. Insoluble fibers, including neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), and crude fiber (CF), were significantly reduced in both the CP and the ETP1-3. The initial NDF value in the FP of 61.01% DM decreased to 35.13% DM for the CP, and to 33.18-33.16% DM for the ETP1-3, but no significant change was observed in the NDF content of cassava peel after treatment with hot water and enzyme solution. The ADF content of the ETP1-3 was 24.01-28.91% DM, which was lower than that of the CP, 31.55% DM, and the FP, 57.00% DM. This means that enzymatic treatment is more effective than hot water treatment in the hydrolysis of ADF. The lowest ADL value of 10.43% DM was obtained for the ETP1, while no significant difference was found for the CP and the ETP2 and the ETP3. This could be due to the fact that after the completion of the first run (ETP1), the same enzyme solution was used for the ETP2 and the ETP3 in the following days. It might be possible that some enzymes were degraded during the first run and storage, resulting in a decrease in the efficiency of ADL hydrolysis for the ETP2 and the ETP3. The crude fiber (CF) content in the FP of 35.01% DM was significantly reduced to 14.36-14.40% DM for both CP and ETP1-3. Overall, both hot water and enzyme treatments were successful in hydrolyzing the insoluble fibers (NDF, ADF, ADL and CF) of cassava peel; however, enzymatic treatment was found to be more effective in hydrolyzing ADF and ADL. Similar results were also discussed by other researchers, who reported the positive effects of amylase, cellulase, and pectinase enzymes under different optimal conditions for the hydrolysis of lignocellulosic materials (2018; 2019; 2020). According to [PERSON] et al. (2018), the crude fiber content of cassava peel and corn cobs subjected to enzyme treatment was reduced by 13.75% and 29.70%, respectively. Many studies have discussed the role of various enzymes in the hydrolysis of cassava peel. However, in this study Viscozyme(r) L was used and the conditions identified by [PERSON] et al. (2018) as optimal for the mechanical peeling of cassava tubers also showed a positive effect on the hydrolysis of insoluble fibers. Therefore, enzymatic pretreatment prior to mechanical peeling could improve the potential for the further use of cassava peel as animal feed or for converting complex carbohydrates to simple sugars through fermentation. Regarding cyanide content, the findings reveal that the enzyme-treated peel (ETP1-3) had a significantly lower cyanide content of 126.61-142.17 \(\upmu\)g g\({}^{-1}\) compared with the cyanide content of the fresh peel which was 308.35 \(\upmu\)g g\({}^{-1}\) and that of the control peel treated with hot water which was 281.75 \(\upmu\)g\({}^{-1}\). The significantly lower cyanide content indicates that enzyme treatment prior to mechanical peeling is more effective in reducing cyanide concentration than hot water treatment. This is due to the ability of the enzyme to hydrolyze, break, and damage the cell wall [43]. Once the cell wall is damaged and cells are disrupted, this does not only promote the release of endogenous linamarase and trapped linamarin, but also accelerates the degradation of linamarin, as reported by [PERSON] et al. [32] and [PERSON] [18]. While there is considerable information in the literature about the role of enzymes in the hydrolysis of cassava peel and the reduction of cyanide content, this research introduces several novel aspects.