Interaction of xanthan gums with galacto- and glucomannans. part I: molecular interactions and synergism in cold gelled systems

Abstract Several studies have investigated xanthan-guar gum (XG-GG), xanthan-locust bean gum (XG-LBG), and xanthan-konjac glucomannan (XG-KGM) blends but little attention has been paid to the physical interactions between the hydrocolloids on a molecular basis. This requires a consistent sample preparation. Often, LBG is heated up to dissolve completely and then xanthan is added, whereas mixtures with guar gum are prepared at room temperature. To understand the synergy during gelation it is necessary to investigate the xanthan-hydrocolloid solutions in the non-heated state because it sets and controls the preferred initial conditions for the given interactions by chain stiffness, charge and polarity under different concentrations In this first part of the publication we focused on blends which are all prepared at room temperature and analysed the molecular interaction in these cold mixed systems. Regarding this, we used Rheology and AFM measurements to characterise the single molecules and the mixing behavior and synergism of the blends. We found, that the cold mixed systems are not stable at room temperature and show a phase separation after one and two days, according to the sample, but are stable when stored at 4 °C. Further, these mixing and demixing properties are highly corresponding to the synergism. Blends with xanthan-guar gum with the weakest mixing properties show the weakest synergism, whereas xanthan-konjac blends with a good mixing behavior exhibit the highest synergism. From the AFM micrographs it was observed that XG-KGM gave most homogeneous mixtures, whereas XG-LBG and XG-GG showed strong phase separation. Based on our experimental results and the characteristics of the molecules such as molecular size, shape and side chains we propose molecular models to explain the physical interactions in these systems which are supported by atomic force microscopy.