A new method for quantitative determination of bitter components of Belgian endive, with a focus on sesquiterpene oxalates

The sesquiterpene lactones typical of the genera Cichorium and Lactuca were historically thought to be present in the free and glycosylated form, but recent developments have highlighted the presence of highly unusual oxalyl esters. In this work, first a liquid chromatography method that requires minimal sample preparation and can measure both free and conjugated sesquiterpene lactones was developed. Then the most common sample preparation techniques used in the past studies (e.g., solid-phase extraction, liquid/liquid extraction) were evaluated and shown to introduce significant bias against the polar oxalyl-terpenes. Finally the method was applied to a case study, highlighting the effect of variety, duration and temperature of forcing on the sesquiterpene lactone content of Belgian endive.