From Fresh to Dried Lavender Flower: Changes in Phytochemical Profile According to Drying Method

Lavandula angustifolia Mill. is a part of the Lamiaceae family, which includes aromatic plants used in perfumery, manufactory, food, ornamental, and medicinal sectors. Both fresh and dried lavender flowers can be exploited in different ways; however, post-harvest treatments such as drying processes can help maintain the flowers' properties for a longer period. This study analyzed fresh (F) and dried lavender flower ultrasound-assisted extracts, comparing two different drying methods, i.e., heat-pump drying (HP) and hot-air drying (HA), to assess potential differences in their effect on the phytochemical composition (total phenolic content, total anthocyanin content, and phenolic profile) and antioxidant activity (FRAP, DPPH, and ABTS assays) of flowers, focusing on three lavender selections from north-western Alps (i.e., Susa, Stura, and Tanaro). Results showed that HP-dried flowers are to be preferred over HA-dried flowers, as they contain +66.73% of phenolics and +62.2% of anthocyanins, and they have higher antioxidant activity (from 60.32% to 284.3% more according to the assay). HP-dried flowers, particularly those from the Tanaro selection, showed also higher values in the relative antioxidant capacity index (RACI) and the global antioxidant score (GAS), ranking together with the fresh flowers. Nine bioactive compounds out of thirteen were detected by means of HPLC, seven in F (caffeic acid, hyperoside, quercetin, ellagic acid, catechin, epicatechin, and dehydroascorbic acid), four in HA (ferulic acid, hyperoside, quercitrin, and epicatechin), and two in HP (caffeic acid and hyperoside). The higher temperatures used in HA probably promoted oxidative and biochemical reactions that led to the presence and increase in these compounds. However, many other phenolic compounds may contribute to the antioxidant power of lavender extracts. Overall, HP resulted in an effective and sustainable method for drying lavender flowers and may have interesting applications to obtain final products richer in bioactive compounds and antioxidant activity to be used in the functional food industry.