Chemical composition of wild Rosmarinus officinalis essential oil: bioactivity evaluation, and valorisation strategies for the spent biomass after essential oil extraction

Minimising waste generation is at the heart of sustainable management policies in the agri-food sector, with a focus on the valorisation of by-products. In this scenario, solid residues from the essential oil (EO) industry are a rich source of bioactive phenolic compounds for use in food and pharmaceuticals. This study explores the potential exploitation of essential oil (EO) and the solid residue produced after the distillation of a wild variety of Rosmarinus officinalis. The EO from the leaves was extracted by hydro-distillation and, afterwards, antioxidant activity and sun protection factor were evaluated, as well the chemical composition was established using gas chromatography. The results of this characterisation reveal a new EO chemotype with the major component being alpha-pinene. The bioactive compounds in rosemary residue after essential oil (EO) distillation were explored. The presence of polyphenols, ortho-diphenols and flavonoids was determined, followed by antioxidant characterisation. The results were analysed using the statistical tool 'Response Surface Methodology' to identify the optimal parameters for maximising the yield of bioactive compounds (time, temperature and solvent concentration) and, so that, the best value of this rosemary by-product could be ascertained. The recovery of terpenes and polyphenols has been demonstrated in this wild variety of R. officinalis for the first time, which allows the full utilisation of its by-products and may help to make the EO industry more sustainable. Furthermore, these research outcomes provide confirmation of the worth of this aromatic plant for application in food, beverages, cosmetics, pharmaceuticals and medicine.