Heat Pump Drying of Lavender Flowers Leads to Decoctions Richer in Bioactive Compounds

Lavandula angustifolia Mill. (Lamiaceae family) is commonly exploited in different sectors, such as cosmetics, perfumery, and medicine because of its phytochemicals. More recently it has gained attention as an edible flower in the food and beverage industry. Post-harvest technologies can help producers to increase the functional beverages market, where there is a growing demand for new products rich in bioactive molecules with beneficial health effects. To maintain lavender flower properties, bioactive compounds have to be effectively preserved after harvesting and processing. This study compared an emerging technology, heat pump drying, with a classical drying approach, i.e., hot air drying, focusing on differences in the total phenolic content, the anthocyanin content, the phenolic profile, and in antioxidant activity of the dried lavender flowers. Three different Italian local lavender flower selections (i.e., Susa, Stura, and Tanaro) were analyzed by means of decoction extraction. Results showed that each one was better preserved in its phytochemical composition by heat-pump drying. Among the lavender selections, Stura and Tanaro showed the highest values for phenolics (2200.99 and 2176.35 mg GAE/100 g DW, respectively), anthocyanins (59.30 and 60.74 mg C3G/100 g DW respectively) and antioxidant activity, assessed through three assays (FRAP, DPPH, ABTS). Four bioactive compounds were detected by means of HPLC, three in the heat pump dried flowers’ decoction (quercitrin, ellagic acid, gallic acid), and one in the hot air-dried flowers’ decoction (epicatechin). Overall, heat pump drying allowed to obtain decoctions richer in bioactive compounds.