Gelling mechanisms of non-starch polysaccharides (NSP) from pre-processed wheat bran fraction

Non-starch polysaccharide (NSP) extracted from pre-processed wheat bran contained arabinoxylan (77%) and beta -D-glucan (23%), and exhibited thermally reversible gelling properties upon cooling to 4 degreesC. Because there are at least two types of polysaccharides present in the NSP, it is important to know which polymer is the component responsible for this gelling behavior. In order to study the contribution of each polymer to the gelling property, two highly specific enzymes were used to depolymerize the individual polymers, namely xylanase (T. Viride, EC 3.2.1.8) for arabinoxylans and lichenase (EC 3.2.1.73) for beta -D-glucans. It was observed that xylanase completely destroyed the gel structure formed by NSP at 2.0% (w/w). In contrast, lichenase did not destroy the gel, but instead enhanced gel strength. It was also found that purified 2.0% (w/w) wheat beta -D-glucan formed a thermally reversible gel, but needed a much longer period to develop a similar gel. No gel was formed at a concentration of 0.5% (w/w), the equivalent beta -D-glucan concentration as exists in 2.0% (w/w) NSP solution. The purified arabinoxylan was able to form a gel, but, the gel strength was much weaker compared to that of NSP. In conclusion, arabinoxylans are the major components responsible for the novel gelling properties of wheat bran NSP; beta -D-glucan, however, assisted the gel formation, possibly through association interactions with the atabinoxylans.