Mechanism of relative humidity-driven cinnamaldehyde from β-cyclodextrin inclusion complexes for antimicrobial...

Precise control over the release of volatile antimicrobials is crucial for industrial applications. Although β-cyclodextrin inclusion complexes (β-CD-IC) enable humidity-triggered release, the mechanisms remain unclear, hindering systematic optimization for practical use. This study characterized β-CD-IC using encapsulation efficiency (82.7 %), loading capacity (7.6 %), X-ray diffraction (XRD), low-field nuclear magnetic resonance (LF-NMR), and volatile antimicrobial assays. The release kinetics of cinnamaldehyde (CIN) were evaluated under five relative humidity (RH) conditions (22 %, 32 %, 55 %, 85 %, and 98 %), revealing that increasing RH enhanced weakly bound water distribution and strengthened water-β-CD interactions, thereby facilitating the release of CIN. At 98 % RH, the cumulative release reached 57.3 % after 7 days, accompanied by complete inhibition against Staphylococcus aureus and Aspergillus niger. XRD and LF-NMR analyses demonstrated that high RH (≥85 %) induced structural reorganization into hydrated cage-like frameworks, while free water formation competitively displaced CIN from the hydrophobic cavity. Molecular dynamics (MD) simulations further elucidated that water molecules preferentially bound to the C6 hydroxyl groups of β-CD, destabilizing the inclusion complex through reduced binding free energy (from -6264.77 kJ/mol at 22 % RH to -4682.34 kJ/mol at 98 % RH) and increased system entropy. These findings offer a theoretical foundation for optimizing β-CD-IC as smart antimicrobial materials in food packaging.