Polyphenols content, antioxidant and anti-inflammatory activity of distillation wastewaters from five species of Lamiaceae family

Background The production of officinal plants is receiving a concrete revaluation in recent years. The wastewaters obtained in the distillation processes of aromatic plants are rich in all the water-soluble and thermostable metabolites, in particular polyphenols. The scope of our work is to contribute to the polyphenolic composition knowledge of wastewaters coming from hydrodistillation of five officinal plants belonging to the Lamiaceae family (Rosmarinus officinalis L., Origanum vulgare L., Origanum majorana L., Salvia officinalis L., and Thymus vulgaris L.) and to evaluate their in vitro antioxidant and anti-inflammatory activities with the intention of laying the foundations for their use in the pharmaceutical and nutraceutical fields. Methods The phytochemical evaluation of the five hydrodistillation wastewaters was carried out through the HPLC-DAD and HPLC/ESI-MS identification of the main polyphenolic compounds. The antioxidant power was evaluated by three in vitro cell-free assays, DPPH assay, ORAC (oxygen radical antioxidant capacity) assay, and SOD (superoxide dismutase)-like activity assay. Finally, their anti-inflammatory potential was evaluated in an in vitro model of acute intestinal inflammation in differentiated Caco-2 cells. Results HPLC analysis evidenced that the highest amounts of active compounds were found in the wastes from S. officinalis and T. vulgaris hydrodistillation, while O. vulgare sample reported fewer active compounds. In all species, organic acid derivatives were the most plentiful fraction, with rosmarinic acid as the most abundant. Flavonoids derivatives were found in lower amounts, and they were mostly represented by flavones, and in lower amounts by flavonols. In four out of five species, the predominant flavonoid was luteolin-7-O-glucuronide, the only flavonoid detected in all species. The antioxidant power as evaluated by the DPPH assay gave the highest response in T. vulgaris and O. vulgare wastes, whereas the measurements in terms of ORAC stressed, besides these two species, the outstanding response of S. officinalis. Furthermore, O. majorana and R. officinalis wastes were also the less effective in terms of SOD-like activity. All the wastewaters investigated showed a significant good anti-inflammatory effect in colonic epithelial Caco-2 cells exposed to the inflammatory cytokine TNF-α. All the samples, in fact, inhibited TNF-α-induced NF-κB inflammatory pathway preventing p65 nuclear accumulation, with a consequent decrease of COX-2 protein levels. In particular, the waters that showed the greatest in vitro anti-inflammatory activity were those from T. vulgaris and O. vulgare. Conclusions In conclusion, our data evidenced that the distillation wastewaters from these five species of Lamiaceae family could represent a new promising source of polyphenolics compounds endowed with antioxidant and anti-inflammatory properties, and their exploitation could enhance the convenience and sustainability of the whole distillation process.