Investigation of the effect of ethanol on the stability of black rice anthocyanin/cyclodextrin inclusion complexes in aqueous systems

BACKGROUND Black rice anthocyanins (BRA) possess antioxidant properties and can alleviate alcohol-induced liver injury but their stability in alcoholic beverages remains a challenge. This study investigated the effects of ethanol concentration on the structural stability of BRA/ β -cyclodextrins ( β -CDs) and their intermolecular interactions. RESULTS At low ethanol concentrations (<164.8 g kg − ¹), hydrogen bonding between cyanidin-3-glucoside (C3G) and β -CD was enhanced whereas higher concentrations (>164.8 g kg −1 ) reduced hydrogen bond formation. The main interactions between β -CD and C3G were hydrogen bonds and van der Waals forces. In contrast, hydroxypropylation of β -CD (HP- β -CD) enlarged the cavity volume, weakening direct hydrogen bonding with C3G; van der Waals forces dominated the binding, and hydrogen bonds originated mainly from surrounding ethanol and water molecules. CONCLUSION Ethanol influenced the stability of the inclusion complexes by modulating the number of hydrogen bonds. High ethanol concentrations (>164.8 g kg −1 ) increased the structural rigidity of β -CD but reduced intramolecular hydrogen bonds within its cavity, leading to decreased stability. In contrast, the hydroxypropyl groups of HP- β -CD enlarged its cavity volume and height, allowing C3G to rely primarily on van der Waals interactions for stability. Consequently, HP- β -CD exhibited greater resistance to ethanol-induced destabilization. © 2025 Society of Chemical Industry.