Influence of cooking process on phenolic marker compounds of vegetables

Phenolic compounds are secondary plant metabolites which have long been associated with flavor and color characteristics of fruits and vegetables. These phenolic compounds attract great interest due to their postulated health protecting properties. However, adequate intakes and absorption rate of phenolic compounds are necessary for these beneficial effects. Until now, little is known about alterations of phenolic compounds content by the cooking process. In the present study, the influence of different volumes of cooking water on the amount of selected phenolic marker compounds resting in the vegetables was assessed. In zucchini, rutin was quantified as a marker for flavonoid glycosides. Chlorogenic acid, representative of phenolic acids was analyzed in carrots. In beans, rutin and quercitrin, both belonging to flavonoid glycosides, were investigated. In potatoes, chlorogenic and caffeic acid were determined. The cooking of zucchini, beans and carrots with smaller amounts of water resulted in significant higher content of phenolic phytochemicals in the vegetables compared to cooking with larger water volumes. For potatoes, which showed great variations in content of phenolic acids after cooking, no significant differences in phenolic acids was observed. It can be concluded from these observations, that real intakes of phenolic compounds from cooked vegetables are lower and that the amounts consumed are therefore overestimated.