Molecular migration of konjac glucomannan and gum Arabic phase separation and its application in oil-water interfaces

Molecular migration of gum Arabic (GA) fragments was investigated, when thermodynamic phase separation occurred in mixtures of konjac glucomannan (KGM) and GA at different concentrations. It has been quantitatively analyzed by GPC-MALLS. After reaching phase equilibrium, GA with the small molecular weight migrated into KGM-rich phase, resulting in a decrease of its relative content (from 13.58% to 0.05%) in GA-rich phase. GA was dyed with fluorochrome, and aggregations of GA in separated phase were recorded using fluorescence microscopy. When KGM content was fixed at 0.4 wt%, increasing GA concentration led to the simultaneous formation of larger aggregates of GA. In the process of phase separation, the amount of coexisted KGM in GA-rich phase decreased as a function of time. To collect the separated phases, the fractionated GA was named as FGA. FGA showed better interfacial properties than original GA, resulting in decreasing of oil-water interfacial tension and increasing of the moduli of interfacial adsorption layer. The proposed reason was that fractions of GA maintained in GA-rich phase, which has proved to possess larger molecular weight, contributed to the better emulsifying capacity. So FGA was the concentrated sample of large molecular fractions that has high emulsifying capacity. Optimized FGA-stabilized emulsions presented small droplet size (around 20 mm), high surface charge at neutral pH (about -30 mV) and high stabilities under various pH range or NaCl concentration. Taken together, this paper provides a flexible method for separating and concentrating GA with high emulsifying capability and has great potentials to be applied in in developing new food ingredients. (C) 2016 Elsevier Ltd. All rights reserved.