An Analysis of the Water Binding in Gels

The water‐binding properties of four gelling macromolecules (carrageenan, agar, potato starch and gelatin) were studied through measurement of the vapor pressure of water in the gels, suction pressure and Flory‐Huggins x‐value developed by the gel, and reduced mobility of water protons as measured by the spin lattice relaxation time from NMR. The difference in water binding between gels could be explained based on hydrogen bonding of water to specific sites and between water molecules; induced water‐water interactions due to hydrophobic regions on the macromolecule; and dipole interactions of water with the ionic sites on the macromolecule. The suction pressure method shows carrageenan and agar to be the best water binders at low concentrations which is illustrated by a decreased x‐value with increased concentration. Gelatin and starch show opposite behavior. The NMR results indicate a different order of water binding due to the difference in cooperative bonding. In this case agar was the best water binder at low a w and gelatin the poorest. This study shows the difficulty that could arise in using only one index of water binding.