It must also be borne in mind that there is a difference in terms of where xylan and glucomannan are located  
Figure 2: Schematic illustration of elastic and plastic deformation, where some pellets can behave elastically and thus expand when pressure is released—causing “springback”. in the secondary cell walls of wood. Xylan is found to be more associated and linked to lignin in comparison to glucomannan, which is more linked to cellulose [28; 29], and whether this affects the color changes correlated to densification is unknown. Another explanation is that a change in color results from polysaccharide degradation. The formation of colored compounds from saccharides has been extensively studied in the field of food chemistry. It was already known in the 1950s that monomeric sugars degrade into low-molecular-weight sugar acids, as well as unknown polymeric compounds [30], both of which can contribute to color as well as taste. Since then, the degradation reactions in question have been studied in numerous systems of varying temperature, pH, concentration and with the inclusion of additional compounds. It turns out that the formation of colored compounds proceed through \(\alpha\)-dicarbonyl intermediates, also known as osuloses [31], which can degrade into acids and aldehydes by means of \(\alpha\)-dicarbonyl cleavage or rearrange by means of benzilic acid rearrangement [32]. Additionally, it is thought that these \(\alpha\)-dicarbonyls can polymerise according to mechanisms that are still not elucidated [33]. The formation of these \(\alpha\)-dicarbonyl compounds can take place in the presence or absence of amino acids. In the presence of amino acids, the formation of \(\alpha\)-dicarbonyl compounds is catalyzed by means of the Maillard reaction; in the absence of amino acids, \(\alpha\)-dicarbonyl compounds are formed by means of caramelization reactions [34]. Caramelization requires elevated temperatures and can be catalyzed by the presence of either acids or bases [35]. The first step of caramelization is the formation of enediols from sugars [36] after which \(\alpha\)-dicarbonyls can form through \(\beta\)-elimination followed by keto-enol tautomerization [32]. However, many of these reactions happen in the absence of moisture and involve condensation reactions; this is in contrast to what has been seen during pelletization, which seems to be stimulated by water [4; 17]. Furthermore, when it comes to densification, pressure is an important parameter, and many of these reactions describe above does not require a high pressure. According to [PERSON] et al. (1991), hydrolysis of hemicelluloses is affected by pressure during treatment [37] and it has been shown that high pressure changes the melting point and glass temperature point to a new equilibrium [8]. However, in these studies, hemicelluloses are mentioned as one component, thus it is unclear which role xylan and glucomannan have. One parameter that affects the hydrolysis of hemicelluloses is the formation, quantity and type of acids alongside the accessibility of the reactants [37]; and correlated to acids, there is a difference between pectin, xylan and glucomannan. Pectin and xylan contain uronic acid residues, whereas glucomannan does not. Uronic acids are known to be able to undergo reactions such as beta eliminations [38], and one hypothesis that [PERSON] et al. presented was that this beta elimination could be the \"starting point\" of the reactions leading to color change [17]. However, [PERSON] et al. only discuss possible explanations and no clarification is given as to where these changes originate from. The purpose of this study was to increase the understanding of how springback effects in pellets can be linked to the polysaccharide substances of biomasses, and how these substances are affected by pressure during densification. The aim was to investigate different maximum pressure, work for compression and the pellet springback effect for cellulose, xylan, glucomannan, pectin and two woods at different moisture contents.