Effect of galacto-oligosaccharide purity on water sorption and plasticization behavior

Galacto-oligosaccharides (GOS) can be produced with different purity levels that were hypothesized to alter water uptake and overall stability. Two purity GOS levels (55% and 90%) in commercially available mixtures were analyzed. Water was found to plasticize GOS (more effectively in the 55% compared to 90% GOS mixture), decreasing the glass transition temperature (Tg) causing the caking of powders and collapse of the amorphous structure. The critical aw for the 55% GOS mixture was between aw 0.23 and 0.33, corresponding to 3.7 and 5.9% moisture, and for the 90% GOS the critical aw was between aw 0.43 and 0.58, corresponding to 9.7 and 13.0% moisture. Differential thermogravimetric (DTG) curves demonstrated that water was more homogenous and difficult to remove as the Tg of GOS fell below storage temperature. DTG trends suggest that this analysis may be used to predict Tg of GOS mixtures, which is influenced by GOS purity level.