Influência da sazonalidade na composição química e nas atividades antioxidante e antimicrobiana das folhas de ora-pro-nobis (Pereskia aculeata Miller)

Abstract

Within the large biodiversity of brazilian flora, the ora-pro-nobis (Pereskia aculeata Miller) started gaining visibility mostly due to the high protein content of its leaves, which made it valuable to feed. Since harvest can occur throughout the year, seasonal variations in composition and activity are normal. With the goal of exploring the biological properties and the chemical components of this specie, considering two sampling seasons of the plant (winter and summer), the drying kinetic of fresh leaves were adjusted to Lewis and Page math models and also was determined the proximate composition of the leaves dried under shade. Furthermore, the extracts of dried leaves were obtained by successive extraction using solvents in polarity gradient – petroleum ether, dichloromethane and ethanol –, to determine phenolic compounds by Folin-Ciocalteau reagent, condensed tannins by Stiasny, antioxidant activity by DPPH, ABTS and FRAP, and antimicrobial activity by disc diffusion and minimum inhibitory concentration (MIC). The fresh leaves presented high moisture content, getting 87.7% in the winter and 85.54% in the summer. Drying kinetic study of P. aculeata leaves showed that experimental data fit better to Page model than Lewis model. Regarding proximate composition, main constituents are carbohydrate, followed by ashes, for both sampling. All of the extracts showed some condensed tannin content, and the ethanolic extract was the richest (47.83% in the winter and 38.71% in the summer). The highest content of phenolic compounds were checked in the ethanolic extract (295.08 mg EAG g-1 in the winter and 336.35 mg EAG g-1 in the summer), followed by dichloromethane extract (244.29 mg EAG g-1 in the winter and 280.79 mg EAG g-1 in the summer). About the antioxidant power, results expressively diverged among the methods DPPH, ABTS and FRAP, which can occurs due to the singularity of each approach and each plant. The extract obtained with petroleum ether, from winter sampling, was the only one which exhibited antimicrobial activity, by manifesting bacteriostatic action against S. aureus bacteria in a minimum inhibitory concentration (MIC) of 2.500 μg mL-1. In general, leaves collected in the summer presented more abundance of components and/or metabolites, except the tannin content of the extracts and the ashes and moisture content of the leaves, which were higher in the winter sampling.