Effect of alcohols on gellan gum gel structure: Bridging the molecular level and the three-dimensional network

This work focuses on the understanding of the interaction of alcohols with gel systems during solvent exchange, following the gel formation. A method of widening the possible alcohol contents in formulations is proposed, as most hydrocolloids have a low tolerance of high alcohol concentrations and in some gelation is completely prevented. Once the CPKelco LA (low-acyl or deacylated) gellan gum gel was produced, different alcoholic solvents (ethanol, 1-propanol, 2-propanol) were used to remove water from the material and replace it, investigating the effect on the gel network as a function of the alcohol chain length. It is the first time that a research paper considers the high-alcohol/gellan gum systems at both the molecular and macroscopic scales, proposing the link between them. Specifically, the interaction of the alcoholic solvents with both the polymer chains and three-dimensional network was evaluated by characterising the physical and mechanical gel properties throughout the alcohol treatment. From this study, the solvent effect on the gelling agent is evident, leading to structure shrinkage and distortion due to a high-induced stress on the gellan gum network. Gradual addition of the alcoholic solution was found to considerably reduce this behaviour due to the slower solvent exchange. As evidence, and to further validate this study on LA gellan gum, both k-carrageenan and gelatin alcogels were investigated, since their gelation mechanism and molecular configuration are respectively similar and different to LA gellan gum. It was found that k-carrageenan reproduced the LA gellan results, unlike gelatin.