In many developing countries, human health problems are solved using local plants. Knowledge of their chemical composition and biological activities can contribute to the creation of natural-based products usefully employed in human health. In this work, we analysed Paederia grandidieri leaves extracted with diverse eco-compatible procedures and subjected to chemical, microbiological, and cellular compatibility assays. Fresh leaves of P. grandidieri were harvested in southern Madagascar, where most of the population relies on P. grandidieri for daily dental care. Leaves were dried and powdered. Distilled water and ethanol at 25 °C and 60 °C from 6 to 24 h were used for extraction. Polyphenol composition, antioxidant activity, and antibacterial, prebiotic, and cytotoxic properties of the extracts were analysed. The aqueous extracts contained higher levels of flavan-3-ols and flavanones, while the hydro-alcoholic extracts were richer in flavonols and flavones. The aqueous extracts showed the highest total phenolic and total flavonoid contents, and antioxidant activity. The hydro-alcoholic extracts showed antibacterial effects against Listeria monocytogenes and Pseudomonas aeruginosa, two key foodborne and environmental pathogens, while the aqueous extracts showed prebiotic effects against Streptococcus salivarius. The cytotoxic effects of P. grandidieri leaf extracts were evaluated using the MTT assay on mouse fibroblasts (L929 cell line). The most cytotoxic extract was the aqueous extract at 25 °C. Given that P. grandidieri is routinely employed by the southern Madagascar population with healthy and strong teeth with fewer cases of tooth decay with respect to other regions, and in light of the significant chemical and microbiological properties, we maintain that P. grandidieri can be a suitable candidate for the production of pro-health products for the oral cavity. More in-depth studies will ensure a broader picture of the impact of extracts, especially for possible oral use.
