## 4 Discussion
### Color Occurrence  
In this study, it was verified that the changes in structure for xylan, as shown in Figure 8 and as has been discussed in earlier papers [4; 17], is related not only to moisture content but also, pressure. As can be seen in Figure 8, xylan at a 5% moisture content, compressed with 5 kN, does not show changes in structure, other than small changes on the top of the pellet. At 14 kN, the color goes from light beige to a browner color and the structure changes at the same time. These changes also increase the hardness of the pellet. As shown in Figure 7, the hardness increases from about 11 kg to about 48 kg. The length of the pellet also differs between 5 kN and 14 kN at 5% moisture content, see Table 3; the green pellet length is 15.21 mm compared to 11.7 mm for 5% moisture content after being pressed with pressure forces of up to 5 kN versus 14 kN. This is important information, because the die presslength directly affects the rollers' pressure by its backpressure and thus, variations in presslengths or lubricating media affect xylan components more than glucomannan components. Based on the results of this study, we further claim that color changes in the xylan pellets are also connected to applied pressure. It is clear that xylan pellets change in color to a much greater extent than the CMC pellets do, as shown in Figure 9. These color changes have also been seen in earlier studies, particularly from more flexible polysaccharides [4; 17], where a hypothesis was that these structural changes result from uronic acid residues [17]. Uronic acid is known to be able to undergo reactions such as \(\beta\)-eliminations [38], which could be the reason behind the color change. However, as shown in Figure 9, there are four tests that generate more normalized absorbance and these are the heat-treated samples, not the pellet samples. The temperature treatment applied to the xylan and CMC powders induced a caramelization reaction and is seen to have resulted in the formation of a significant amount of color. Specifically, the xylan powder is seen to result in ten-times more color than the CMC powder, as measured in normalized absorbance (see Figure 9). According to [PERSON] and [PERSON], who compared the caramelization kinetics of glucose and wheat flour systems, enolization of the saccharides is the rate-determining step of the caramelization pathway: in order for enolization to occur and for caramelization to be initiated, a certain amount of molecular mobility is required [36]. Therefore, in that study, sugar compounds with lower melting points were found to achieve more color. A similar trend can be observed regarding the powders in the present study: since CMC could be speculated to have a higher melting point than xylan, it would not have been unreasonable to expect a lower amount of normalized absorbance. However, color changes in xylan pellets do not show the same trend as heat-treated powder samples. While the xylan pellet samples do show a higher absorbance than their CMC counterparts, this is seen even for their untreated variants (see Figure 9), and there are no significant differences in color between samples of the same raw material. This was interesting, since it has been previously observed in the literature [40] that both moisture and temperature have an effect on the formation of color, the reason again being induced mobility, which mitigates the formation of the rate-determining-enol intermediary. The lack of difference in color from these variables in the present study suggests, however, that the color difference of the pellets is not chemical in nature at all. Instead, it would seem to be the result of physical changes in the structure, perhaps due to increases in scattering as a result of the applied pressure.