Increasing demand for natural bioactive ingredients extracted from Aromatic and Medicinal Plants (AMPs) has produced disposal problems associated with residual solid waste. One of the main sectors interested in the exploitation of AMPs is the Essential Oils (EOs) industry. Nevertheless, EO is the main commodity and represents only a small part of the AMPs used, generally less than 5% (w/w). This results in the production of a noteworthy quantity of biomass that has no apparent commercial value and is therefore underestimated and underutilized by the EOs industry.
Among AMPs, Rosmarinus officinalis L., commonly known as rosemary and belonging to the Lamiaceae family, is an aromatic plant endemic to the coastal area of the Mediterranean region but spread all over the world. Rosemary can be cultivated or grow wild, as an ornamental evergreen shrub. Their leaves are usually used fresh or dried to flavor foods, mostly in traditional Mediterranean gastronomy. The antioxidant activity of the leaves is acknowledged and is ascribed to EOs and rosemary extracts. Moreover, rosemary extracts are food additives approved for use in Europe.
To the best of our knowledge, the optimization of polyphenols recovery from rosemary residues after EO extraction has not yet been investigated. Hence, in the present study, the EO extraction from rosemary leaves was performed by using the hydro-distillation method, and the antioxidant (EC50) and sun protection (SPF) activities were also evaluated. The polyphenolic fraction was extracted from rosemary residue acting on some experimental variables. In particular, in this research the extraction time (15 min, 30 min, and 60 min), the temperature (25°C, 40°C, 50°C, 60°C, and 70°C), and the ethanol concentration (50%, 60%, 70%, and 80%) were tuned. In this study, an EO yield of 1.57% was obtained with an EC50 value of 240.39 µL/mL and a SPF of 2.55. The maximum amount of polyphenols extracted from rosemary residue was 24.14 mg GAE/g DW, achieved by using an 80% ethanolic solution at 70°C for 60 min.
This study reveals how exploitation and consequential valorization of AMPs solid waste may represent new answers to circular economy strategies adopted by European countries.
