Besides, their activity levels are 20–30 times higher, in comparison to that of endo-β-d-xylanase. At low pH values (3.7–4.5), however, the α-l-arabinofuranosidase activity is about two times higher than that of β-d-xylosidase (Rasmussen et al., 2001). This is in line with the results of our study that showed decreased Ara/Xyl ratio of bread WE-AX. Another option is that the WU-AX solubilised during breadmaking may display much lower arabinosylation degree than the native WE-AX of rye flour, and therefore, significantly affect the branching degree of the overall AX population in the
bread. Nevertheless, Obeticholic Acid considering a typical low pH values of rye dough, a partial hydrolysis of acid-labile arabinofuranosyl substituents may occur as well. In the case of WU-AX, the changes in the
branching degrees during breadmaking of two types of bread were inverse (Fig. 2B). Much like WE-AX, the breadmaking of wholemeal bread resulted in decrease Lumacaftor mouse of their Ara/Xyl ratio. Instead, those of endosperm breads had higher Ara/Xyl ratios than corresponding WU polysaccharides in starting flours. They were characterised by the highest Ara/Xyl ratios (on average, 0.73 and 0.77, respectively for flour and bread). The highly branched AX regions form a steric barrier for AX-hydrolysing enzymes, above all, for endo-β-d-xylanase action that requires at least five adjacent unsubstituted xylopyranosyl residues in the backbone. Therefore, apparently enzymatic hydrolysis of densely substituted WU-AX of endosperm flour seems to be hardly possible. Though the entire WU population present in endosperm flour exhibits high Ara/Xyl ratio, it is highly heterogeneous
and contains many subfractions differing in branching degrees (Ara/Xyl ratio, 0.48–1.23) (Cyran, Courtin, & Delcour, 2004). It has been demonstrated that AX solubilised from WU fraction of rye endosperm flour by sequential treatment with IKBKE Ba(OH)2, water and NaOH contained 50%, 35% and 17% of lowly branched populations with Ara/Xyl ratio of 0.5, which were built almost exclusively of un- and mono-substituted xylopyranosyl residues. Such populations are susceptible to enzymatic digestion and their hydrolysis may represent an explanation for an increase in branching degree of AX left in the WU fractions of endosperm bread. Similarly, acid hydrolysis can be involved in the above process. Unlike the WU-AX of rye endosperm flour, those from wholemeal with much lower overall branching degrees (Ara/Xyl ratio, 0.55–0.60) are enriched in lowly substituted populations, originating mainly from outer grain layers (Cyran & Saulnier, 2007). They are characterised by lower Ara/Xyl ratios (0.31–0.38) and contain also populations with markedly low (0.18–0.20) and extremely low (0.07–0.11) ratios of Ara/Xyl.