DIMETHYL CARDAMONIN FROM CLEISTOCALYX OPERCULATUS LEAVES: OPTIMISED EXTRACTION CONDITIONS AND INHIBITIVE ACTIVITY AGAINST FOOD-POISONING BACTERIA

In this study, the predominant phenolic compound of Cleistocalyx operculatus leaves harvested in Vietnam was identified as 2’,4’-dihydroxy-6’-methoxy-3’,5’-dimethylchalcone (also called dimethyl cardamonin) by using UHPLC-DAD-HRMS. The extraction of this compound from leaves was optimised using response surface methodology. A second-order polynomial model with three important variables (ethanol concentration, temperature and extraction time) was used. A rotatable central composite design consisting of 17 experimental runs with three replicates at the center point was applied to describe the experimental data as the dimethyl cardamonin apparent content of leaves. The experimental results fit well to the model with R 2 equal to 0.9618 and without a lack of fit. The optimised conditions were as follows: 80% ethanol, 85 °C and extraction time of 22 min. These conditions were applied to produce the extract from C. operculatus leaves. The obtained freeze-dried extract powder exhibited inhibitive activity against five food poisoning bacterial strains belonging to Staphylococcus aureus , Vibrio parahaemolyticus , Escherichia coli , Salmonella and Listeria monocytogenes species, with the inhibitive zone ranging from 1.83 to 9.17 mm. The antibacterial activity of the extract was dose dependent. The results indicated the potential application of C. operculatus leaves as a source of natural antimicrobial agents for food preservation.