Characterization of Bioactive Phenolic Compounds Extracted from Hydro-Distillation By-Products of Spanish Lamiaceae Plants

Plants of the <i>Lamiaceae</i> family are widely used for the extraction of essential oils, and this industry generates a large number of solid residues as by-products, which contain non-volatile valuable compounds. The aim of this work was to identify and quantify the phenolic compounds present in these solid residues from different important Spanish species of <i>Lamiaceae</i> to characterize and valorize them. Forty-seven phenolic compounds were identified by HPLC-DAD-MS and quantified by HPLC-DAD. Different concentrations and types of phenolic compounds were found between the solid residues. The <i>Rosmarinus officinalis</i> extracts showed the highest total phenolic content due to their high phenolic terpene concentrations. The <i>Thymus mastichina</i> extracts were characterized by kaempferol and flavanones, and some flavones were derived from luteolin and apigenin. Finally, the sample <i>Lavandula</i> and <i>Salvia lavandulifolia</i> extracts presented the lowest content of most phenolic compounds, with the exception of some phenolic acids, such as danshensu, salvianolic acid A, and glucosides of hydroxycinnamic acids. Therefore, this work provides information on the quantification of a large number of phenolic compounds using a simple, sensitive, reproducible, and accurate methodology. In addition, the results indicate that these solid residues still contain important amounts of different polyphenols, which are antioxidants and can be used in different industries.