Convection and Microwave–Convection Drying of Moldavian Dragonhead (Dracocephalum moldavica L.) Leaves

Moldavian dragonhead leaves are a valuable waste product from the production of seed oil, from a nutritional point of view. It has been shown that dried leaves can be used for the production of functional foods. Despite the wide possibilities of using dried Moldavian dragonhead leaves, research on the selection of drying methods is scarce. This particular study investigated the traditional convection and the hybrid microwave–convection methods to dry Moldavian dragonhead leaves. We showed that the convection method supported by microwaves allowed us to obtain dried leaves in a much shorter time than traditional convection drying (the convection drying lasted, depending on the parameters, 184-75 min, while the convection–microwave drying lasted 33-7 min). Moreover, the microwave–convection-dried leaves contained more polyphenols (the average TPC in the convection droughts was 29.532, while in the microwave–convection droughts, it was 41.880 mg GAE/g d.m.) and chlorophylls (an average of 2.326 in the convection-dried and 2.675 mg/g d.m. in the microwave–convection-dried material) and were characterized by significantly higher antioxidant activity, compared to convection-dried ones.