Valorisation of Arbutus unedo distillers' grains for topical applications: NADES extraction via conventional and pressurized techniques

During the production of Arbutus unedo (A. unedo) spirit, large quantities of distillers' grains are generated. These by-products are rich in phenolic compounds (PCs), a family of molecules well known for their antioxidant activity. This study investigates the valorisation of this waste stream by extracting bioactive compounds to produce antioxidant rich extracts for direct incorporation into cosmetic formulations.Maceration and pressurized liquid extraction (PLE) were selected as extraction techniques, using natural deep eutectic solvents (NADES) as extractants. The obtained extracts were evaluated for total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity (AA). Screening experiments revealed that NADES outperformed conventional solvents (water and aqueous ethanol mixtures), with Proline:Propylene Glycol (1:4) containing 65 mol% water yielding the best results. Response surface methodology (RSM) was then applied to optimize AA in maceration by varying extraction temperature, NADES ratio, and water content. The extract with the highest AA was obtained using Pro:PPG with a proline molar fraction of 0.41, 14 mol% water, at 58 °C, and 30 min extraction time. PLE further improved AA compared to the optimized maceration results, using Pro:PPG (1:4) with 65 mol% water at 75 °C, 1500 psi, and two extraction cycles of 15 min each.The optimized extracts from both maceration and PLE were incorporated into cosmetic formulations, and their rheological properties were characterized. This work represents the first study to explore the use of A. unedo distillers' grain extracts in cosmetics.