pH controlled gelation behavior and morphology of gelatin/hydroxypropylmethylcellulose blend in aqueous solution

Studies on unique blends of cool and thermal gels have attracted increasing attention since they both have scientific and commercial importance, such as functional food design and edible packaging materials etc. In this work, the pH dependent gelation behaviors and morphologiesof blends of a cool gel, gelatin (GA), and a thermal gel,hydroxypropylmethylcellulose (HPMC), in aqueous solution were investigated by rheometer, UV spectrophotometer, fluorescence microscope (FM) and environmental scanning electron microscopy (ESEM). It was found that when pH < 4.75, HPMC was the continuous phase, while GA was the separated phase distributed in HPMC matrix as small spherical domains. Phase transition occurred at pH 5.00, in which GA became the continuous phase, while HPMC appeared as separated droplets dispersed in GA matrix. At lower pH values, GA and HPMC were compatible based on UV detection, ESEM observation, as well as phase separation kinetics. Near the isoelectric point (pI) of gelatin (pH 7.0-9.0), a maximum viscoelastic module (G') was detected. It was noticed that there were many interphasic regions in the blend systems. Each phase was not pure: GA phase contained some HPMC and vice versa at all pH values, which means that GA and HPMC are partly miscible or compatible to a certain degree.