Table tomato leaves are a sustainable source of rutin and display antioxidant, antihemolytic and antimicrobial activity

Table tomato (Solanum lycopersicum L.) is highly consumed worldwide and its annual production generates a considerable amount of plant by-products [1]. Although tomatoes are well-known for their composition in nutrients and bioactive compounds [2,3], little information is available in literature regarding tomato leaves, probably because these by-products have no commercial value. Therefore, considering the enormous production of this biomass and the current trends of circularity and sustainable development [3], this study was carried out to evaluate the polyphenolic composition and bioactive properties of tomato leaves resulting from the regeneration of table tomato landraces conserved ex-situ in the Portuguese Genebank (BPGV), in Braga, Portugal. The tomato plant material resulting from pruning performed after the flowering season was lyophilized and ground to a fine powder, used to prepare hydroethanolic extracts [4]. These extracts were characterized for their composition in polyphenols (by HPLC-DAD-ESI/MSn) and used to evaluate the antioxidant (by DPPH• scavenging capacity and reduction power), antihemolytic (using sheep erythrocytes and AAPH as a free radical generator), and antimicrobial (tested against food-borne bacterial and fungal strains by the serial microdilution and p-iodonitrotetrazolium violet colorimetric methods) activities [4]. The chromatographic analysis allowed identifying phenolic acids and flavonoids, with prevalence of quercetin-3-O-rutinoside (rutin). The leaf extracts showed antioxidant activity, with EC50 values lower than those previously reported for the respective tomato fruits, thus translating a higher activity [2]. The extracts were also effective in some extent in protecting the erythrocytes from the oxidative hemolysis caused the thermal decomposition of the free-radical initiator AAPH. Despite their low activity against the tested microfungi, some extracts had ability to inhibit and kill some bacteria (including Salmonella typhimurium, Listeria monocytogenes, Bacillus cereus, and Enterobacter cloacae) more effectively than the antibiotic ampicillin. It was concluded that table tomato crop by-products can be used to produce rutin-rich extracts with antioxidant and antibacterial activities for possible use in the agri-food sector as natural preservatives.