Preliminary observations of flavonoid glycosides from the vegetable coagulant Cynara L. in protected designation of origin cheeses

Aqueous extracts of Cynara cardunculus L. (cardoon) flowers have been used for centuries as vegetable coagulants for traditional cheesemaking in the Iberian Peninsula. However, the full chemical composition of the extract that is added to the milk has never been studied. In this study we investigated the phenolic components of the aqueous extracts from cardoon flowers and their detection in cheese. Analysis by HPLC-diode array detection (HPLC-DAD) revealed the presence of one flavonoid-7-glycoside (isorhoifolin) and the aglycones apigenin and luteolin. Another major flavonoid-7-glycoside (apigenin-7-O-glucuronide) was also identified and its structure elucidated by 13C-NMR. This represents the first report of these compounds in the aqueous extract of cardoon flowers. These compounds were also found in cheese curd made using this coagulant but were not present in the original milk, leading to the suggestion that these phenolic compounds could be used as authentication markers for cheeses made using cardoon extracts as the coagulant.