Maturation of demineralized arabinogalactan-proteins from Acacia seyal gum in dry state: Aggregation kinetics and structural properties of aggregates

Abstract

The aggregation in dry state of mineral-loaded arabinogalactan-proteins (AGPs) from Acacia seyal gum (GA) generally occurs above 70 °C. This study focuses on the aggregation sensitivity of AGPs after their demineralization. The dry incubation in mild temperature (25 °C to 70 °C) of demineralized AGPs induced the formation of aggregates, not observed with GA. AGPs aggregated following a self-assembly mechanism for which temperature only modulated the aggregation rate. The activation energy was around 90-100 kJ·mol^-1 that could correspond to chemical condensation reactions induced by the AGPs surface dehydration. The aggregation kinetics were characterized by the formation of soluble aggregates during the first times of incubation, whose molar mass increased from 1 · 10⁶ g·mol^-1 to 6.7 · 10⁶ g·mol^-1 (SEC MALS) or 12 · 10⁶ g·mol^-1 (AF4 MALS) after 1.66 days of dry heating at 40 °C. These soluble aggregates revealed they adopted a similar conformation to that of not aggregated AGPs with a ν_h value around 0.45. Above 1.66 days at 40 °C, the soluble aggregates grew up to form microparticles with sizes ranging from 10 to around 200 μm. This study highlighted the protective role of cations from AGPs whose demineralization increased their sensibility to dry heating and their chemical reactivity for aggregation.

Keywords: Acacia gums; Aggregation; Arabinogalactan-proteins; Demineralization; Dry heating; Microparticles.