Enhanced solubility and antimicrobial activity of alamethicin in aqueous solution by complexation with γ-cyclodextrin

Alamethicin (ALM) inhibits the growth of bacteria by disrupting their cell membrane. ALM exhibits poor solubility in aqueous medium thus limiting its application. A method is proposed for encapsulation of ALM with gamma-cyclodextrin (gamma-CD) by forming a complex of higher solubility with thermal and pH stability as confirmed by FT-IR and DSC, thus greatly improving its application in food safety. Molecular dynamics simulation suggested a stable configuration of the complex when hydrophobic residues are inserted into the hydrophobic cavity of gamma-CD. Aggregation of the complex was inhibited at higher gamma-CD/ALM molar ratio. gamma-CD/ALM complex exhibited significant antimicrobial activity against L. monocytogenes with the minimum inhibitory concentration being dependent on gamma-CD/ALM molar ratio ( > 0.429 mg/mL for 1:1; > 1.094 mg/mL for 5:1; > 2.078 mg/mL for 10:1). Optimum gamma-CD/ALM molar ratio for maximum antimicrobial activity is the result of competing effects of higher solubility and shielding of hydrophobic ALM groups by gamma-CD.