Análise fitoquímica, avaliação da atividade antioxidante e antimicrobiana de Solanum guaraniticum A. St.- Hil

Abstract

The Solanaceae family is one of the largest and most complex, especially the Solanum genus, with about 1500 species. Solanum guaraniticum is a shrub found in Paraguay, Argentina and Brazil, popularly known as jurubeba or false jurubeba. This study aimed to quantify the main classes of secondary metabolites and determine the antimicrobial and antioxidant activities of the leaves of S. guaraniticum. The plant material was collected in the city of Guaporé, RS, Brazil, and is registered in the herbarium of the Biology Department at the Federal University of Santa Maria under number SMDB13158. The leaves of the plant were dried, triturated and macerated with ethanol (70%) for seven days. After this period, the material was filtered and the extract concentrated in rotary evaporator to obtain the aqueous extract. Part of this was taken to complete dryness yielding the crude extract (CE), another part was successively fractionated with chloroform (CHCl3), ethyl acetate (AcOEt) and butanol (BuOH), yielding the respective fractions. In the antioxidant and phytochemical analysis, the AcOEt fraction showed the highest amount of polyphenols (546.57 ± 2.35 mg of gallic acid equivalents/g) and the best antioxidant capacity by DPPH method (IC50 = 9.11 ± 0.75 μg/ mL). The CHCl3 fraction showed the highest contents of tannins (56.03 ± 0.68 mg of catechin equivalents/g), flavonoids (75.73 ± 0.34 mg rutin equivalents/g) and alkaloids (10.79 ± 0.06 mg/g), being more effective in scavenging reactive species, by inhibition of dichlorofluorescein oxidation (DCFH-DA), also showing the best activity of inhibition of lipid peroxidation by the TBARS method, as well as inhibition of protein oxidation, by the protein carbonyl method. HPLC analysis of CE and fractions revealed the presence of caffeic, chlorogenic and rosmarinic acids, very active phenolic acids that may be involved in the activities described. Regarding antimicrobial activity, assessed by broth microdilution, good activities were observed against Gram-positive bacteria, especially for CE (MIC of 32 μg/mL for M. luteus) and the AcOEt fraction (MIC of 64 μg/mL for S. intermedius and L. monocytogenes). The extracts were practically inactive against Gram-negative bacteria and inactive against fungi. It was also verified promising antimycobacterial activity, mainly to the CHCl3 fraction against M. smegmatis (MIC = 156 μg/mL). The results contributed to reveal some phytochemical characteristics of this species, and show that S. guaraniticum possesses considerable antimicrobial and antioxidant potential.