Chemical, Biochemical, Antimicrobial, and Pharmacological Assessment of Postdistillation Waste Material Extracts of Mentha x piperita

<b>Background:</b> Aromatic plants like peppermint (<i>Mentha</i> x <i>piperita</i>, Lamiaceae) have a long tradition of use. Most of the plant material is used to produce herbal drugs and for the isolation of essential oils. However, since essential oils are present in very small amounts, the largest proportion of plants remains unused. <b>Objectives:</b> The aims of this study were the analysis of chemical, biochemical, antimicrobial, and pharmacological properties of peppermint waste material extracts (derived from stems, post-distillation waste, and deodorized leaves) in comparison with the officially prepared extract. <b>Results:</b> The obtained results revealed that the investigated peppermint waste extracts (PWEs) are a rich source of phenolic compounds, where rosmarinic acid was determined as the dominant one (7.05-21.19 mg/g d.e.). Antioxidant potential and hepatoprotective effect of PWE were comparable with the official extract, where the most active ones were those prepared by treating the deodorized leaves with both 45% and 75% ethanol. In addition, PWE exhibited notable antimicrobial and anticholinesterase activity. Results of pharmacological studies on experimental animals showed that peppermint extracts (official and those made from deodorized leaves) did not interfere with the effect of the tested drugs, midazolam and fluoxetine. The examined extracts neither exerted an influence on motor coordination nor acted as antidepressants. Results of the elevated plus maze test indicated that PWE affected the activity of the central nervous system. <b>Conclusions:</b> PWEs represent a significant source of phenolic compounds, especially rosmarinic acid, and they can be used in the pharmaceutical industry to produce various herbal products and in the food industry as natural additives.