Flavonoids are among the most abundant natural bioactive compounds produced by plants. Many different activities have been reported for these secondary metabolites against numerous cells and systems. One of the most interesting is certainly the antimicrobial, which is stimulated through various molecular mechanisms. In fact, flavonoids are effective both in directly damaging the envelope of Gram-negative and Gram-positive bacteria but also by acting toward specific molecular targets essential for the survival of these microorganisms. The purpose of this paper is to present an overview of the most interesting results obtained in the research focused on the study of the interactions between flavonoids and bacterial proteins. Despite the great structural heterogeneity of these plant metabolites, it is interesting to observe that many flavonoids affect the same cellular pathways. Furthermore, it is evident that some of these compounds interact with more than one target, producing multiple effects. Taken together, the reported data demonstrate the great potential of flavonoids in developing innovative systems, which can help address the increasingly serious problem of antibiotic resistance.

Bromelain is a mixture of cysteine endopeptidase usually extracted from pineapple juice and is used for the treatment of various human diseases and in industrial applications. Bromelain demand is quickly increasing, and its recovery from pineapple residues appears to be a sustainable waste management strategy. Pineapple core is among the most significant waste materials in the production of canned pineapple and is richer in bromelain than other pineapple residues. In this project, we compared the enzymatic properties and composition of bromelain extracts from either pineapple core or pulp to address the recovery of bioactive bromelain from pineapple core, thus contributing to the valorization of this waste material. Although significant differences were detected in the protein content of the two preparations, no differences could be detected for their proteolytic activity and for the effect of pH on their enzymatic activity. Mass spectrometry (MS) approaches identified the same peptidases in the fruit and in the core. This confirmed the possibility of using pineapple core to obtain relevant amounts of bioactive bromelain by applying a relatively simple procedure, thus paving the way to implementing a circular economy in this specific industrial sector.

A comparative quali-quantitative study of the peel extracts of eight Punica granatum cultivars obtained from underexploited areas of South Italy was carried out in order to valorize them as health-promoting by-products. The results showed that all of the samples possessed 45 ellagitannins, consisting mainly of polyhydroxyphenoyls; 10 flavonoids, belonging to flavonol, flavone, and catechin classes; and 2 anthocyanins. The most representative compounds underwent quantification through a LC-MS/MS multiple reaction monitoring (MRM)-based method; their qualitative profile was almost superimposable, while variability in the quantitative phenolic content was observed. The antioxidant activity was investigated using cell-free and cell-based assays. The in vitro anti-inflammatory potential was also studied by monitoring three typical markers of inflammation (IL-1β, IL-6, and TNF-α). Moderate differences in both activities were observed between the cultivars. Results showed that all of the investigated peels have a potential use as healthy bioactive phytocomplexes due to the interesting antioxidant and anti-inflammatory activities; in particular from the bioinformatic approaches a series of compounds, including galloyl-, pedunculagin- and ellagic acid-based, were found to be highly correlated with bioactivity of the extracts. Finally, the bioactivities showed by a Campanian local cultivar, ‘Granato di Aiello del Sabato’, could promote its cultivation by local farmers and germplasm conservation.

In developing countries, crop deterioration is mainly caused by inappropriate storage conditions that promote insect infestation. Synthetic pesticides are associated with serious adverse effects on humans and the environment. Thus, finding alternative “green” insecticides is a very pressing need. Calotropis procera (Aiton) Dryand (Apocynaceae) growing in Saudi Arabia was selected for this purpose. LC-MS/MS analysis was applied to investigate the metabolic composition of different C. procera extracts. Particularly, C. procera latex and leaves showed a high presence of cardenolides including calactin, uscharidin, 15β-hydroxy-calactin, 16β-hydroxy-calactin, and 12β-hydroxy-calactin. The ovicidal activity of the extracts from different plant organs (flowers, leaves, branches, roots), and of the latex, against Cadra cautella (Walker) (Lepidoptera, Pyralidae) was assessed. Extracts of C. procera roots displayed the most potent activity with 50% of C. cautella eggs not hatching at 10.000 ppm (1%).

Calabrian Glycyrrhiza glabra is one of the most appreciated licorice varieties worldwide, and its leaves are emerging as a valuable source of bioactive compounds. Nevertheless, this biomass is usually discarded, and its valorization could contribute to boost the economic value of the licorice production chain. In this study, the effects of production area and harvest time on the specialized metabolite content of G. glabra leaves (GGL) and also the antioxidant and anti-aging properties are evaluated to explore the potential of this untapped resource and to select the most optimal harvesting practices. GGL exhibited high levels of specialized metabolites (4–30 g/100 g of dry leaf) and the most abundant ones are pinocembrin, prenylated flavanones (licoflavanone and glabranin), and prenylated dihydrostilbenes. Their levels and antioxidant capacity in extracts are influenced by both production area and harvest time, showing a decisive role on specialized metabolites accumulation. Interestingly, GGL extracts strongly attenuate the toxicity of α-synuclein, the intracellular reactive oxygen species (ROS) content, and cellular senescence on Saccharomyces cerevisiae expressing human α-synuclein model, showing great potential to prevent aging and age-related disorders. These results provide insights into the phytochemical dynamics of GGL, identifying the best harvesting site and period to obtain bioactive-rich sources with potential uses in the food, nutraceutical, and pharmaceutical sectors.