Hot and cold drying of edible flowers affect metabolite patterns of extracts and decoctions

Edible flowers are rich in bioactive compounds and pigments that are on increasing demand in nutraceutical, medicinal, food, cosmetic and dyeing industries. This study evaluated the anthocyanins, phenolics and antioxidant activity of eight edible flowers (Bellis perennis L., Centaurea cyanus L., Dianthus carthusianorum L., Lavandula angustifolia Mill., Primula vulgaris Huds., Rosa canina L., Rosa pendulina L. and Viola odorata L.) after 24 h of hot drying (50 °C; natural convection stove) or cold drying (CD) (22 °C; heat-pump drying system). The hot-dried and cold-dried materials were then used to prepare ultrasound-assisted extracts, which are used as food additives or as a source of natural colourants, or decoctions (DECs), which are used for herbal teas. The edible flower UAEs and DECs had high amounts of anthocyanins (up to 3,284.6 mg C3G · 100 g-1 ), phenolics (up to 9,034 mg · 100 g-1 ) and antioxidant activity (866 mmol TE · g-1 , 4,901 mmol Fe2+ · kg-1 ), with roses having the highest amount. The anthocyanin content and phenolic profile (flavonols, benzoic acids, cinnamic acids and flavanols) of edible flowers are found to be affected by drying and extraction methods. For decoctions, CD was found to be the most efficient drying method for all the parameters. For UAEs, CD resulted in a higher anthocyanin content, while hot drying resulted in a higher phenolic content, particularly flavanols. Overall, the studied edible flower extracts and decoctions can contribute to healthy and coloured substances, which can be used for designing innovative natural products. Rosa pendulina and R. canina are the most promising sources.