Dissolution kinetics of guar gum powders - II. Effects of concentration and molecular weight

This study investigated and compared the hydration rate of commercial samples of galactomannan-rich guar gum of different average molecular weights (M-w) and concentrations. An empirical logarithmic model, developed in a previous paper for describing the hydration kinetics of guar gum. powders, was used for this purpose. The hydration rate was found to be dependent on the galactomannan concentration. In the intermediate galactomannan concentration range (0.5-1.2% w/v) of one of the relatively high-M-w samples, the hydration rate increased with increase in concentration. For the more concentrated systems (>1.2% w/v) of the same sample, an increase in concentration appeared to suppress the hydration process, thus reducing the hydration rate. As might be expected, molecular weight (M-w) had a significant effect on the hydration rate of guar gum. Using guar samples with a M-w range of 0.1-2.8 million, an inverse relationship between M-w and hydration rate was demonstrated. However, one high-M-w sample produced a significantly lower hydration rate than that predicted from this relationship. This apparently anomalous result can be explained by the observation that in this sample there was a variation in the M-w distribution with respect to particle size. This indicates that particle size (and distribution) and M-w are crucial factors in determining net hydration rates. (C) 2003 Elsevier Science Ltd. All rights reserved.