Reconsidering the Encapsulation Mechanism: The Influence of Substitution Degree and Substitution Position of HP-β-CD on Inclusion Behavior

Abstract

Hydroxypropyl-β-cyclodextrin (HP-β-CD) is a widely used food-grade encapsulating agent for hydrophobic bioactive compounds, but its inclusion behavior is conventionally evaluated only by the degree of substitution (DS), while the influence of substitution position (SP) remains underexplored. In this study, eight HP-β-CD samples were characterized by 1H and 13C NMR to determine their DS and SP and were used to encapsulate Mosla chinensis essential oil. Moderate substitution (DS 5–6), dominated by C2/C3 substitution with limited C6 modification, produced the highest encapsulation efficiency (83.49%), loading capacity (7.42%), and aqueous solubility (7.97 mg/mL), together with improved component retention during 90-day storage. Excessive substitution, particularly elevated C6 substitution, increased steric obstruction and reduced overall inclusion performance. Molecular simulations indicated that HP-β-CD and carvacrol binding was mainly stabilized by van der Waals interactions and hydrogen bonding. These findings demonstrate that DS and SP, are important structural descriptors for selecting HP-β-CD delivery materials.