Changes in molecular structure of citrus pectin in acidic environments at ambient temperature

The environmental pH regulates the chemical structure and functional properties of pectin, but the structural changes, especially in acidic environments at ambient temperature, have not been studied. In this study, as acidity increased from pH 7.0 to 1.0, the molecular weight of pectin decreased gradually from 1.90 × 10⁵ to 0.36 × 10⁵ g/mol, while the size of the HG region increased from 75.37 % to 85.49 % with an increased degree of esterification. Notably, visualization tools, chemical methods, and molecular dynamics simulations were used to analyze conformation. The transition from molecular dispersal, dominated by electrostatic repulsion, at neutral pH to molecular aggregation, dominated by hydrogen bonding and hydrophobic forces in an acidic environment, was elucidated. The pectin molecules changed from loose structures (Rg 17.3 nm; D_max 115 nm) at pH 7.0 to a compact conformation (Rg 15.0 nm; D_max 98 nm) at pH 2.0. Our study would improve the understanding of the effects of an acidic environment on pectin structure and function in practical processes, from farmland to storage, processing, and dietary digestion.