Tree bark represents an abundant and underutilized renewable resource of bioactive compounds with promising potential for application in advanced dermal and cosmetic products, such as wound healing and skin care. This study reports, for the first time, the glycerol-based extraction of bark from three industrially significant European tree species: birch ( Betula pendula ), black alder ( Alnus glutinosa ), and Scots pine ( Pinus sylvestris L.). Extracts obtained using water and water-glycerol mixtures across a range of temperatures were systematically evaluated for their phenolic composition, antioxidant and antimicrobial efficacy in vitro, and potential for dermal delivery. Based on these results, a sustainable, phenolic-oriented extraction strategy using glycerol as both solvent and carrier for transdermal delivery is proposed. Although glycerol does not maximize total extract yield, it enriches phenolic compounds. Glycerol-based extraction of black alder bark at 40°C temperature concentrated diarylheptanoids while minimizing solubilization of carbohydrates and proanthocyanidins. The diarylheptanoid-enriched glycerol extracts efficiently protected a cosmetic emulsion in accelerated oxidation tests and exhibited high radical-scavenging and antimicrobial activity against Escherichia coli . Incorporated into wound-dressing hydrogels, these extracts demonstrated rapid transdermal diffusion in skin penetration assays. These findings indicate that glycerol-based extraction at moderate temperatures provides an energy-efficient and effective approach to obtain bioactive-rich formulations from forestry wastes suitable for direct application in wound dressings and cosmetic products. • Glycerol–water mixtures selectively extract phenolic compounds from alder bark. • Comparable phenolic profiles at 40°C and 85°C enable lower-energy extraction. • Glycerolic extracts of alder bark exhibit antioxidant and antibacterial activities. • Diarylheptanoids from alder and birch bark show favorable skin permeability. • Glycerol-based extraction provides a new route for high-value bark valorization.
Gosselink et al. (Sun,) studied this question.