Effect of arabinose substitution on the material properties of arabinoxylan films

Arabinoxylans have been demonstrated to form films with low oxygen permeability and have a potential application as a barrier material in the food packaging industry. The arabinose content and the distribution of arabinose along the xylan chain vary depending on the botanical source and are strongly affected by the extraction process. This study was undertaken in order to investigate the effect of arabinose content on film properties. The substrate used was a rye arabinoxylan that had an arabinose to xylose ratio of 0.52 and an average number molecular weight of 305 kDa. Oxalic acid was used to attempt selective removal of the arabinose substituents on the xylan main chain. The debranching of the polymer was coupled with a decrease in molecular weight. The effect of reaction conditions on the decrease in arabinose content and loss of molecular weight was investigated. Optimal conditions were selected using an experimental design. Treatment at lower temperature for longer period of times resulted in debranching with less degradation of the main chain. As the arabinose to xylose ratio was lowered, aggregates began to form in an interval of the ara/xyl ratio between 0.31 and 0.23 in a water solution. Precipitation occurred below an ara/xyl ratio of 0.1. Thus, removal of arabinose substituents results in a gradual association of unsubstituted chains. There is a linear correlation between arabinose substitution and the moisture content of arabinoxylan at 98% RH. A decrease in arabinose content resulted in the loss of a plasticizing effect, as determined by dynamic mechanical analysis, which is correlated to water binding capacity