# Utilization of the Nutritional Potential of Wheat Bran Using Different Fractionation Techniques
## 2 Cereals and Their Potential Nutritional Benefits
The amount and structure of arabinoxylans vary depending on the cereal species, variety, anatomical location, and environmental conditions during grain growth and maturation [28; 29]. Furthermore, small amounts of xyloglucans are found in wheat bran, which are mainly derived from the pericarp. Glucomannans and arabinocalactans, which originate from aleurone and endosperm cells, are also present in minute amounts [28]. [PERSON] et al. reported that wheat bran contains 18.8-21.4% arabinoxylans on a dry weight basis [30]. Arabinoxylans are formed by the main chain of \(\upbeta\)-linked (1 \(\longrightarrow\) 4)-D-xylopyranose and are mainly substituted with the side chains of \(\upalpha\)-l-arabinofuranose. Arabinoses are attached to the \(O\)-2 and/or \(O\)-3 position of the xylose units Figure 2[31]. The rate of arabinose/xylose (A/X) substitution of arabinoxylans increases from the center of the endosperm towards the outer layers of the wheat kernel. The most substituted arabinoxylans are in the pericarp, where on average one xylose carries one arabinose [28]. Some arabinose units are ester-linked to \(O\)-5 by ferulic acid [32]. [PERSON] et al. reported that 31% of unsubstituted xylose and 24% of monosubstituted and 39% of disubstituted xylose are found in wheat bran [33]. Arabinoxylans are divided into water-extractable (WE-AX) and non-water-extractable arabinoxylans (NW-AX) [32]. Approximately 30% of the 2.5% of all arabinoxylans present in wheat flour endosperm are water-extractable. In contrast to the non-water-extractable arabinoxylans, they are not maintained in the cell wall by covalent and non-covalent interactions with other arabinoxylan molecules or with cell wall components such as proteins, lignin, or cellulose. It can be assumed that WE-AXs are loosely bound to the cell wall surface. Several factors are involved in the ability to extract arabinoxylans with water, including incomplete cross-linking with other components, small structural differences, or initial enzymatic degradation in the grain [34]. We-AXs from wheat bran are less substituted with arabinose than those from the inner endosperm. The lower degree of substitution is due to a higher proportion of unsubstituted xylose residues and a lower proportion of disubstituted xylose residues. Since wheat bran is composed of different grain tissues, the actual structure of araboxylans in wheat bran is very heterogeneous. The araboxylans in wheat bran are mainly low-substituted ones, with an arabinose/xylose (A/X) ratio of 0.2, and then highly substituted ones, with an A/X ratio of 1 [35]. Arabinoxylans also serve as an important reservoir of antioxidant phenolic compounds, including alkylresorcinols and phenolic acids. Ferulic acid is very often bound directly to arabinylan. Various technological treatments have been investigated to facilitate the release of ferulic acid and other bound phenolic compounds from the arabinoxylan structure to exploit their antioxidant potential. These treatments include thermal, alkaline, enzymatic, ultrasonic, and fermentation treatments. In addition, recent studies have shown that the degree of substitution and molecular weight have a significant effect on the antioxidant potential of arabinoxylans. Lower degrees of substitution led to higher antioxidant capacity of arabinoxylans. Water-extractable arabinoxylan fractions treated with endovascular also exhibited higher antioxidant capacity [31]. From a technological point of view, arabinoxylans play an important role in the preparation of bread. Both WE-AXs and NW-AXs contribute to an increase in water absorption, but their effect on baking properties seems to differ. The insolubility of NW-AXs causes them to trap water, which limits the amount of water available for the development of the gluten complex. WE-AXs, on the other hand, increase the viscosity of free water in the dough during absorption [36]. Arabinoxylans have interesting functional properties for use as food additives. They have applications as viscosity enhancers, as they have a high water retention capacity.