Bioactive compounds in hop leaves: from synthesis factors to practical applications

In recent years, consumer preference for organic and sustainably produced products has changed significantly. Growing demand has prompted both farmers and industry to rethink and adapt their production methods. This change in consumer behavior is having a profound impact on the way the industry approaches production and is driving innovation in the area of sustainability. Another consequence is that research is also focusing on new strategies for obtaining these biomolecules. In this context, recycling and reuse agri-food waste seems to be the best solution from an economic and ecological point of view. Based on these considerations, the doctoral project focused on the use of hop plants as a source of biomolecules, in line with the 2030 Green Agenda. The hop plant, known for its cones used in beer brewing, has much more to offer and my research aimed to highlight this untapped potential. In fact, while the cones are the main product harvested for their economic value in beer production, the rest of the plant, including the leaves and stems, is usually discarded as waste and represents a burden for the farmers. Over the last three years, this research has characterized the hop vegetative biomass in terms of bioactive compounds, in order to individuate several potential applications and increase the sustainability of the hop culture. The research has been carried out in three research lines: i) Open field - Hop leaves: a source of bio-compounds ii) Hop biomass -from waste to resource; iii) Bioactive compounds from vitro- derived hop plantlets: a green opportunity. On closer inspection, the first research line focused on the biochemical and molecular characterization of leaves collected from plants of ten hop varieties at the time of cone harvesting; moreover, only for the cv. Cascade, one of the most widely grown hop varieties, the development of the biochemical leaf profile during the growing cycle was investigated. In particular, the bioactivity of the leaf extracts against food-borne and additionally the possible interaction with proteins such as human insulin, amyloid beta peptide, mucin and bovine serum albumin (BSA) was evaluated, indicating their potential to counteract inflammatory processes and protect against Alzheimer’s disease. Thanks to the collaboration with Packtin srl, a company partner of this research program, that uses innovative techniques to process plant and food waste, hop vegetative biomass was dried and pulverized to obtain a powder that was characterized and employed in different application fields. Specifically, after a biochemical characterization, hop biomass powder was used, in collaboration with University of Palermo, as ingredient in bakery product and, in collaboration with University of Ferrara, its extracts were evaluated for crop protection. Hop biomass powder confirmed its high content bioactive compounds; in detail, when added to bread, hop biomass powder improved its organoleptical and nutritional quality, extending, also, its shelf life. Extracts obtained with different solvents were tested in vitro and in vivo against the bacterium Xanthomonas campestris pv. campestris and showed promising antibacterial activity. The results demonstrated the effective antimicrobial activity of these matrices. In addition, the high efficacy, environmental compatibility and associated sustainability as well as the low cost and low toxicity make these extracts an ideal means of controlling black rot in cruciferous crops. The possibility of converting hop waste into valuable by-products opens up new opportunities for the industry and offers environmentally friendly alternatives that can reduce the amount of waste and increase the sustainability of production processes. To further explore the potential of hop vegetative biomass, in vitro culture techniques have been applied to work independently from the seasonal constraints that normally affect hop production in the field and, moreover, guarantees a continuous and standardized supply of biomass to stakeholders. Hop plant (cvs. Cascade, Columbus, Gianni and Magnum) in vitro multiplication was carried out at the University of Parma to obtain the vegetative biomass for further characterization. Specifically, biomass obtained in vitro from all four varieties was analysed in terms of biochemical and molecular properties, which also provides information on the potential of in vitro cultivated hop plants as a source of bioactive compounds. In another study, four different cytokinins added to the culture medium were tested for the cvs. Cascade and Columbus at the Catholic University of Valencia to increase the production of biomolecules. The results of the growth parameters and biochemical tests showed a strong influence of the genotype on the response of the plant. Specifically, in cv. Columbus, the addition of cytokinins reduced plant growth, but triggered the synthesis of (poly)phenols and molecules with antioxidant activity. In the last two studies, carried out in collaboration with the University of Palermo, the effects on growth parameters and the stimulation of secondary metabolism were investigated by modifying the culture system and the culture medium composition. In particular, the use of the temporary immersion system (TIS), in comparison with culture on solid medium, with or without sucrose, was tested on the cv. Cascade; while on the cv. Columbus only TIS was carried out evaluating different immersion times and the influence of sucrose in the culture medium. In conclusion, research conducted during this PhD has demonstrated that hop plants are a valuable resource that goes far beyond their traditional use in brewing. The leaves, stems and even the vitro derived materials offer promising applications in a wide range of industrial applications, contributing to sustainability and reducing waste.