Extraction of macroalgae phenolic compounds for cosmetic application using eutectic solvents

Abstract

Cosmetic industry remains a major focus of economic development in the 21st century, while consumer's demand for sustainability drives the search for new active natural ingredients and the development of green extractions techniques. The aim of this work is to obtain antioxidant-enriched extracts from two seaweeds found on the Portuguese shore, Sargassum muticum and Gelidium corneum using natural deep eutectic solvents (NADES) to be used in cosmetic formulations. Extracts were obtained by maceration of powdered seaweeds with aqueous solutions (25 % (v/v) in water) of different NADES, L-lactic acid: fructose (5:1), L-lactic acid: glucose (5:1) and L-lactic acid: sodium acetate (7:1). The resulting extracts were evaluated regarding their total phenolic content (TPC) using the Folin-Ciocalteu method and antioxidant capacity by the DPPH and FRAP assays. L-lactic acid: fructose (5:1) NADES yielded Sargassum muticum extracts with the highest phenolic content (2099 mg GAE/L) and the highest antioxidant activities (DPPH reduction of 27 %, FRAP 30 μM FeSO4). Antimicrobial activity of the extracts over three microorganisms of the skin microbiota, the bacteria Staphylococcus epidermidis and Cutibacterium acnes and the fungus Malassezia furfur, revealed no relevant antimicrobial effect, meaning that extracts did not affect the skin microbiota homeostasis. The extract with the highest cosmeceutical interest, S. muticum extract prepared using L-lactic acid: fructose (7:1), was incorporated into a topical O/W emulsion. Physical and rheology data of the cosmetic formulation ensure its quality and safety. Finally, compatibility, acceptability and antioxidant efficacy were evaluated in vivo, in human volunteers. The results show that NADES are a promising replacement of conventional solvents in the extraction of antioxidants from biomass and their use in topical formulations is safe.