Phytochemical Profile and In Vitro Bioactivities of Plant-Based By-Products in View of a Potential Reuse and Valorization

Wastes and by-products of plant origin are of particular interest to develop a circular economy approach, which attempts to turn them into resources. In this work, thirty-seven neglected plant matrices, including agricultural residues, pest plants, and by-products from the herbal and food industry were extracted and tested for their in vitro anti-tyrosinase, antioxidant, and antibacterial activity against the phytopathogens Pseudomonas syringae pv. syringae ATCC 19310 and Clavibacter michiganensis subsp. nebraskense ATCC 27822. Antioxidant activity ranged from 0.3 to 5 mg of Tr. eq/mL of plant extract, and extract of Castanea sativa pericarp (Csp), Rosa damascena buds (post-distillation) (Rod), and Prunus amygdalus exocarp and mesocarp (Pam) were the most powerful ones. Csp was also capable of inhibiting tyrosinase (IC50 = 16.5 mu g/mL), as well as three distillation by-products, namely: Cupressus sempervirens (Css) (IC50 = 95.5 mu g/mL), Salvia officinalis (Sco) (IC50 = 87.6 mu g/mL), and Helichrysum italicum (Hei) (IC50 = 90.1 mu g/mL). Five residues from distillation showed antibacterial activity against C. michiganensis (MICs ranging from 0.125 to 1 mg/mL), namely: Salvia sclarea L. (Sas), Salvia rosmarinus Schleid (Sar), Sco, Hei, and Css. The H-1 NMR fingerprinting of the bioactive matrices was acquired, detecting primary and secondary metabolites (rosmarinic acid, shikimic acid, sclareol, and hydroxycinnamic acids).