The pH-responsive phase separation of type-A gelatin and dextran characterized with static multiple light scattering (S-MLS)

Abstract

Macromolecular phase separation has attracted increasing attention due to its wide applications in food industry, such as modulating food texture and delivering bioactive compounds. The phase separation kinetics is important but rarely reported due to the limitation of current methods. This work provided an effective method, static multiple light scattering (S-MLS), for the study of phase separation kinetics, and investigated the effects of pH on the phase separation of type-A gelatin and dextran mixtures (GE/DE) using S-MLS technique, fluorescence microscopy and visual assessment. Phase diagrams of GE/DE (1.0–6.0 wt%) at pH 3.00–11.0 were measured based on the micro-phase separation. Interestingly, GE/DE mixtures were likely to be miscible at low and high pHs. GE/DE (4.0 wt%/4.0 wt%) mixture at pH 3.00–10.0 was selected for following study. Phase separation of GE/DE (4.0 wt%/4.0 wt%) mixture was pH-responsive, e.g. no phase separation at pH 3.00–4.75 and pH 10.0, only microphase separation at pH 5.00 and 5.25, and both micro- and macro-phase separation at pH 5.50–9.00. The order of phase separation rates was pH5.50 > pH6.00 > pH9.00 > pH7.00 > pH8.00. Based on the results of S-MLS, micro- and macro-phase separation images, phase separation process was proposed to be divided into four steps, including droplet coalescence, droplet migration, primary and stable phase separation. The variation of the GE/DE interaction and the self-aggregation of GE as a function of the pH might explain the pH-response of GE/DE phase separation. S-MLS is an effective method to study the phase separation kinetics of macromolecular systems.