Gelation of gellan induced by trivalent cations and coexisting trivalent with monovalent cations studied by rheological and DSC measurements.

The effect of trivalent cation Fe3+ on the gelation process of a sodium salt form of gellan (DG, deacylated gellan gum) was investigated by rheology and DSC studies. On addition of a fairly low concentration of Fe3+ (1 mM), both the complex modulus (G*) of a 1.0 % DG solution in gel state and the sol-gel transition temperature (Tgel) slightly decreased. At higher Fe3+ concentrations (2 and 3 mM), however, a slight increase in the G* and Tgel was observed. In the coexisting monovalent cation (K+) solutions, addition of Fe3+ always improved the G* in gel state and the Tgel in a concentration-dependent manner. Moreover, for all Fe3+ DG solutions, the ordered structure formation temperature (Torder) was always lower than Tgel and increased with increasing Fe3+ concentration. This finding indicates that the network formation in the DG solutions should occur in advance of the ordered structure formation of the DG chains and that the presence of Fe3+ unfavorably affected the conformational transition of DG. In coexisting cation solution, the presence of K+ ion made a favorable contribution to the binding of Fe3+ to the disordered DG chains and to the subsequent ordered structure formation of the DG chains.

Fabrication and characterization of alginate-zein core-shell microcapsules for controlled release of buckwheat honey.

In this study, extrusion method was employed to fabricate alginate-zein core-shell microcapsules loaded with buckwheat honey by dropping alginate and buckwheat honey mixture solution into a 70.0 % zein ethanol solution(v/v) containing 5.0 % CaCl2 solution (wt%). The microcapsules were constructed by two parts: 1) the formation of hydrophilic beads through the crosslinking of alginate chains with Ca2+; 2) the introduction of alginate beads into the aqueous zein ethanol solution which decreased the ethanol concentration, prompting the precipitation of zein and the deposition of zein nanoparticles onto the surfaces of alginate beads. Comparing with the alginate beads, the prepared microcapsules not only possessed better water-holding capacity, but also achieved controlled release of buckwheat honey. Importantly, the microcapsules significantly retained the antioxidant activity of the buckwheat honey. Therefore, this innovative method for fabricating alginate-zein core-shell microcapsules can suggest a promising approach to broaden the application of buckwheat honey in the food field.