# Valorization of Cassava By-Products: Cyanide Content and Quality Characteristics of Leaves and Peel
## 3 Results and Discussion  
### Quality Assessment and Cyanide Level of Cassava Leaves following Screw Pressing  
The results of screw pressing frozen cassava leaves reveal the unequal distribution of the original ingredients between their fractions: juice and press cake. Figure 3 shows that the press cake contains a high proportion of dry matter and organic matter compared to the juice fractions, indicating that press cake can be used in the production of high-quality silage. However, the ash content was higher in the juice part than in the press cake. This is due to the fact that some minerals were leached during the pressing process, resulting in a greater amount of ash in the juice. These findings are consistent with those of [PERSON] et al. [27], who observed a similar trend during the mechanical pressing of cassava leaves. As for crude protein content, a reasonable amount of protein was found in the frozen leaves (27.09% DM), as well as in the juice (25.47% DM) and press cake (23.82% DM). The protein value of the juice fraction was higher than that of the press cake, which is in contrast to the results found by other researchers [3; 27] who reported a high protein content in the press cake. This difference could be explained by the fact that most of the proteins in leaves are bound in the fibrous structure [36], which typically leads to a higher protein content in the press cake during mechanical pressing. However, in the present study, frozen leaves were used, and freezing as a pretreatment resulted in cell breakage and the release of cell components [28], including soluble protein, leading to a high protein content in the juice fraction. Despite this difference, there was no significant distinction in the protein content of frozen cassava leaves and their fractions, suggesting that they have great potential for protein extraction for use as food or feed. Several researchers have identified the related amount of protein in cassava leaves from different varieties of the plant. For instance, [PERSON] et al. [14] reported protein content ranging from approximately 19 to 25% DM in three cassava varieties. In another study, [PERSON] et al. [37] obtained protein concentrations in cassava leaves from four varieties ranging from 17.7% to 24% DM. [PERSON] et al. [21] found a protein content of 33.6% DM in young cassava leaves. However, it should be noted that the quality and quantity of protein in cassava leaves and their fractions may vary due to differences in variety, harvest age, climatic conditions, soil properties, freezing or storage time, pressing, and extraction methods. Figure 3: Dry matter, organic matter, ash, crude protein, and cyanide content of frozen cassava leaves, juice and press cake. Different letters for the same parameter represent significant differences (\(p<0.05\)). The cyanide results in Figure 3 show that the initial cyanide content of 399.23 \(\mathrm{\SIUnitSymbolMicro g}\)\({}^{-1}\) DM in the frozen leaves decreased to 105.55 \(\mathrm{\SIUnitSymbolMicro g}\)\({}^{-1}\) DM in the press cake, but increased to 788.38 \(\mathrm{\SIUnitSymbolMicro g}\)\({}^{-1}\) DM in the juice portion. This indicates that most of the cyanide content was removed with the juice part during the crushing process, and pressing alone was effective in obtaining a press cake with low toxicity. Moreover, freezing and thawing prior to pressing causes a disruption in leaf tissue and cells, which may also contribute to a greater reduction in cyanide by releasing the bound cyanide and facilitating the interaction of linamarin with endogenous linamarase. [PERSON] et al. (2018) reported that freezing tissues with a high moisture content causes the formation of ice crystals within the cells and this ruptures the cell membranes, leading to a leakage of cells and their contents. Since cyanide is water-soluble, it can be trapped in the ice crystals and released upon thawing, and thus is easily leached out with the juice fraction during pressing.