Complex coacervates formation between gelatin and gum Arabic with different arabinogalactan protein fraction content and their characterization

This work aimed to investigate the possible impact of the chemical composition of gum arabic (GA) on the interactions and complexation mechanism with gelatin (G). For this purpose, two gum arabic samples were selected differing in the content of their arabinogalactan protein fraction (AGP), i.e. low (7%, GA7) and high (14%, GA14). The complex coacervates formation process was studied as a function of pH (from 7 to 2.4) and G:GA mixing ratio (1:2, 1:1, 2:1, 4:1, 6:1 w/w) by following changes in turbidity, zeta-potential and absorption of methylene blue - biopolymers mixtures. The complexation between the biopolymers (G-GA7 and G-GA14) was found to be stronger at a ratio of 1:1 and pH 3.7, where the highest yield (similar to 71%) was observed. The formed coacervates were examined using laser diffraction technique and optical microscopy along with Scanning Electron Microscopy, Fourier Transform Infrared analysis and Differential Scanning Calorimetry. Although both G:GA systems exhibited a similar behavior, some differences were observed. More specifically, results revealed that GA14 affected the surface charge characteristics of the G-GA complexes to a greater extent than GA7, while the corresponding liquid coacervates were more spherical, with a smoother surface and not aggregated. Additionally, G-GA14 complex coacervates were characterized by a more uniform morphology and size distribution along with a higher thermal stability implying thus a greater effectiveness of this system for the encapsulation of heat-sensitive materials.