Changes in antioxidant properties and volatile compounds of kaffir lime leaf as affected by cooking processes.
Kaffir lime leaf is one of important spices used in eastern cuisines especially in Thai food and that has been cooked in many ways. Our present study investigated the effect of cooking methods on phenolic compounds and antioxidant properties as well as volatile compounds of kaffir lime leaf. Six commonly used cooking methods including three hydrothermal processes, namely blanching, boiling and steaming, and three non-hydrothermal processes, namely frying, roasting and drying, were evaluated. The results showed steaming provided the highest values of total phenolic and total flavonoid contents along with antioxidant activities determined by in vitro DPPH and FRAP assays while drying with hot air gave the lowest values of those parameters tested. Critonella was the predominant volatile compound in fresh leaf (56%) which was enhanced by all non-hydrothermal processes however it was significantly decreased by all water involving processes. In contrast, beta-citronellol was increased by blanching and boiling but decreased by other cooking processes. Our findings suggest that different cooking methods caused various effects on the phenolic compounds and antioxidant properties of kaffir lime leaf. The presence of different volatile compounds in kaffir lime leaves cooked by each process may be a reason of a unique flavor to the food.