Molecular characterization of conformational properties and molecular association of cereal beta-glucans

The molecular characterization of cereal beta-glucans was carried out in the present study. A carbanilation method was developed for molecular weight determination of cereal pglucans, the chemical substitution of the hydroxyl groups by phenyl carbamate prevented the formation of intermolecular hydrogen bonding. The carbanilates (DS ∼ 2) were molecularly dispersed in 1, 4-dioxane allowing the accurate molecular weight determination. The conformational analysis suggested a porous globular structure for the partially carbanilated beta-glucans. A new approach of computer modeling was used to build 3D molecular models of beta-glucans and study their conformational properties. The moderately extended sinuous chain conformation was visualized. The calculated conformational parameters agreed with the experimental results obtained from dynamic and static light scattering methods and suggested that the chain stiffness of beta-glucans increased with the tri/tetra ratio. It was demonstrated that the molecular association behaviours of cereal beta-glucans mainly depend on their structural features, the solvent quality and solution concentrations. The interactions between the consecutive cellotriosyl units are mainly responsible for the aggregation behaviour, hence formation of gels. Diffusion limited cluster aggregation (DLCA) regime is suggested in dilute aqueous solutions, which is featured by faster aggregation rates and more opened aggregate structures; in contrast, a reaction limited cluster aggregation (RLCA) regime was evidenced in dilute salt solution and concentrated solution, where the intra-chain interaction and excluded volume effect could play important roles for gel net work formation. The effects of molecular weight and tri/tetra ratio on molecular association of cereal beta-glucans were revealed by the current study. In DLCA regime, higher molecular weight and tri/tetra ratio led to a weaker ability for forming aggregation as evidenced by a more opened aggregate structure and lower aggregation number. However, in RLCA regime, with the decrease of molecular weight and increase of tri/tetra ratio, the aggregation abilities is increased, which lead to faster formation of gels and formation of stronger gels. It is advised that the observations and results of current study are only true when the molecular weight is higher than the minimum molecular weight for gel formation (which is yet to be determined). The present study provides the fundamental information on molecular association and network formation of cereal beta glucans, which are essential for establishing the relationships between physiological effects and structural and functional properties of cereal beta-glucans, thus favours their applications in food.