Molecular encapsulation of a key odor-active 2-acetyl-1-pyrroline in aromatic rice with β-cyclodextrin derivatives

Abstract 2-Acetyl-1-Pyrroline (2AP) is a key volatile compound contributing to a characteristic popcorn-like odor in several Asian aromatic rice varieties. Even though the demand for 2AP has been continuously increasing in global markets, its instability is a significant problem for commercial and food applications. Beta-cyclodextrin (βCD) has been extensively used to improve the stability, solubility, and sensorial properties of many hydrophobic and volatile compounds via an encapsulation process into its hydrophobic inner cavity. In this work, molecular complexation between 2AP and βCDs (hydroxypropyl (HP) and methyl (M) analogs) was theoretically and experimentally investigated using molecular dynamics (MD) simulation, molecular mechanics/generalized Born surface area-based free energy calculation, and gas chromatography–mass spectrometry (GC-MS). Triplicate 500 ns MD simulations revealed that, among six studied βCDs, only 6-HPβCD and 2,6-DMβCD derivatives could stably form inclusion complexes with 2AP, driven mainly by van der Waals interactions. The pyrroline ring of 2AP was preferentially embedded in the hydrophobic interior of 2,6-DMβCD, whereas the pyrroline and acetyl moieties of 2AP were freely rotated inside 6-HPβCD along the simulation times. The binding affinity, the compactness, and the number of atomic contacts of 2AP/2,6-DMβCD complex were higher than those of 2AP/6-HPβCD system, in good agreement with the highest remaining 2AP in the 2AP/2,6-DMβCD complex from GC-MS result. Altogether, the obtained theoretical and experimental data demonstrated the good potentiality of 2,6-DMβCD as suitable host molecule for 2AP encapsulation.