pH-modulated enhancement of β-cyclodextrin encapsulation for cinnamon essential oil: A protonation-driven strategy

Cinnamon essential oil (CEO) possesses significant antimicrobial and antioxidant properties for food preservation, but its practical application is hindered by poor stability and high volatility. In this study, β-cyclodextrin (β-CD) was employed in combination with a novel pH-modulation strategy using three natural organic acids—L-ascorbic acid (L-AA), L-malic acid (L-MA), and citric acid (CA)—to enhance CEO encapsulation efficiency. Results showed that, at a 0.30% regulator concentration, maximum encapsulation efficiencies were achieved: CEO/L-AA/β-CD (95.25%) > CEO/L-MA/β-CD (89.55%) > CEO/CA/β-CD (87.25%) > CEO/β-CD control (80.02%), representing an approximately 19% improvement. Notably, efficiency did not correlate linearly with acidity. 1 H NMR analysis revealed that moderate acidity (pH 3.10, L-AA) promoted cinnamaldehyde protonation and optimal cavity penetration, while excessive acidity (pH 2.63, CA) caused undesirable “surface anchoring”. Molecular simulations demonstrated a stronger binding affinity for protonated cinnamaldehyde (ΔG = −10.87 vs. −8.63 kcal/mol), driven by enhanced electrostatic and van der Waals interactions. The formation of inclusion complexes (ICs) was confirmed by SEM, FT-IR, XRD, and TGA-DSC, revealing a crystalline-to-amorphous transformation. L-AA-modulated complexes exhibited superior thermal stability and antioxidant retention, attributed to effective pH regulation and the inherent antioxidant properties of L-AA. This pH-modulation strategy offers a promising approach for essential oil encapsulation in food applications. • pH modulation raises β-CD encapsulation of cinnamon essential oil to 95.25%. • Cinnamaldehyde protonation enhances host-guest binding affinity by 26%. • 1 H NMR and MD simulations elucidate protonation-driven binding mechanism. • Encapsulation efficiency is non-linearly related to acidity strength.