Elucidating the impact of intermolecular forces on the formation and internal structure of high-methoxyl pectin aggregates

Achieving controllable aggregation of high-methoxyl pectin (HMP) and regulating the structure of resulting aggregates is crucial for tailored functional properties. We investigated the aggregation of HMP and the internal structure of HMP aggregates at varying conditions of SDS, urea, pH and NaCl, aiming to reveal the impact of different intermolecular forces. We discovered that HMP molecules self-assembled into aggregates comprising hydrophilic microdomains enclosing discrete hydrophobic microdomains. Reducing hydrophobic interactions and hydrogen bonding among HMP molecules using SDS and urea increased the critical aggregation concentration (CAC), resulting in smaller aggregates with internal hydrophobic microdomains of higher polarity and lower average aggregation number (N_agg). Decreasing electrostatic repulsions didn't impact the CAC of HMP and the polarity and N_agg of the internal hydrophobic microdomains, but can significantly reduce aggregate size. This study can deepen our understanding of the practical structure of pectin in solutions and guide customized encapsulation and emulsifying properties of pectin.