Direct observation of the structure of phase separation in FITC-KC/LC mixed carrageenan gels

The structure of phase separation in fluorescein isothiocyanate (FITC)-labeled kappa carrageenan (KC)–nonlabeled lambda carrageenan (LC) mixtures was investigated using low-level covalent labeling to prevent the influence of labeling on the phase separation behavior. Rheological, differential scanning calorimetry (DSC), and gel permeation chromatography (GPC) analyses confirmed that low-level labeling did not alter the physical, thermal, and molecular weight properties of KC. Fluorescence microscopy revealed phase separation in the FITC-KC/LC gel at 0.1% (w/w) labeling, which shows the KC-rich and LC-rich regions. These findings demonstrate that low-level covalent labeling enables direct visualization of the phase separation in mixed carrageenan gels with no effect on their phase separation behavior.