Effect of Heat Treatment on Hydrolysis of Luteolin Glycosides

Abstract

Paprika contains high amounts of the functional flavonoid luteolin. However, the naturally occurring compounds luteolin-7-O-(2-apiosyl-6-malonyl)-glucoside (L-7-AMG) and luteolin-7-O-(2-apiosyl-glucoside) (L-7-AG) have low absorption rates in the body. We investigated whether the heat supplied during cooking would result in the conversion of L-7-AMG and L-7-AG to the more absorbable luteolin-7-O-glucoside (L-7-G). L-7-G was stable at pH 3 and 5 and was not hydrolyzed, while L-7-AG was hydrolyzed to L-7-G at pH 3 and maintained total luteolin. L-7-AMG underwent continuous hydrolysis to yield L-7-AG and L-7-G at pH 3 and above 100°C. At pH 7, the total luteolin content decreased in all glycosides. These results indicate that a temperature of 100°C or higher and acidic conditions (pH 3) are desirable for obtaining low molecular weight luteolin glycosides.