Abstract

Introduction: Guarana (Paullinia cupana) is a native Amazonian fruit and, due to its medicinal properties, stands out as one of the most promising species of Brazilian flora. Known for its invigorating and stimulating action, this species produces phenolic compounds responsible for its biological activities, which are of great interest to the phytocosmetic industry, in the preparation of anti-aging creams, for example. In this study, the antimicrobial, antioxidant, photoprotective and cytotoxic activities of extracts obtained from guarana seeds were evaluated.  

Methods: Guarana seeds were obtained in Maués, Amazonas state, Brazil and, after drying, the seeds were ground in a knife mill. P. cupana seed extracts were obtained by the depletion method using hexane, dichloromethane and ethanol as solvents. Antioxidant activity assays were performed to determine the ability to scavenge the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH•). To assess the sun protection factor (SPF), Mansur's spectrophotometric method was used. For the analysis of antimicrobial activity, the microplate dilution technique was used against strains of Escherichia coli, Pseudomonas aeruginosa and Candida albicans. To evaluate the toxicity of the extracts, the lethal concentration of 50% of the population of the microcrustacean Artemia salina was determined. The cytotoxic effect of the extracts against human colorectal carcinoma cells (HCT 116) was also evaluated using the Alamar Blue test.  

Results: The ethanolic extract from guarana seeds showed SPF value of 249.10 and a critical wavelength number (λc) of 383 nm, when evaluated at a concentration of 0.1% (m/m). The ethanolic extract also showed antioxidant activity, and a 50% efficient concentration (EC₅₀) of 647 μg mL^-1. The dichloromethane extract was active against E. coli and P. aeruginosa, with a minimum inhibitory concentration (MIC) of 20 mg mL^-1 for both bacteria, and a MIC of 2.0 mg mL^-1 for the yeast. This extract did not show toxicity against A. salina (LD₅₀> 1 mg mL^-1). The ethanolic and hexane extracts, however, presented low toxicity to the microcrustacean. On the other hand, none of the evaluated extracts inhibited the proliferation of HCT116 cells, showing no cytotoxicity.

Conclusion: P. cupana seeds have an important therapeutic value due to the presence of substances with antioxidant, antibiotic and photoprotective activities, though with low cytotoxicity, which allows their use as functional additives in phytocosmetics, as well as in the development of possible phytotherapeutic products.