Phenolic and volatile compounds, total protein content, antioxidant and antidiabetic activities of leaves of Palicourea padifolia (Rubiaceae)

Background and Aims: Information on the chemical composition and biological activities of Palicourea padifolia is scarce. This study aimed to 1) measure the total content of nutrients, macroelements, proteins, and secondary metabolites, 2) conduct metabolomic analyses on phenolic and volatile compounds, and 3) assess the antioxidant and antidiabetic activities from the leaves of this species. Methods: The total content of nutrients and macroelements was determined by spectroscopic, spectrometric, and spectrophotometric approaches. The total content of alkaloids, terpenes, phenols, flavonoids, tannins, and proteins was determined by spectrophotometric approaches. Volatile and phenolic compounds were identified by gas and liquid chromatography, respectively, coupled to mass spectrometers. The antioxidant activity was determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2’-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays, and the antidiabetic potential was determined by the inhibition of α-glucosidase. Key results: The leaves of P. padifolia were rich in Ca, Na, and Mg and exhibited a low protein content. The leaf methanolic extract (LME) contained high levels of alkaloids, phenols, and terpenes, while flavonoids were present at low concentrations. The major phenolic compounds identified were chlorogenic acid, scopoletin, trans-cinnamic acid, and (-)-epicatechin. In addition, a leaf petroleum ether extract (LPE) contained mainly phytol, palmitic acid, (Z)-7-tetradecenal, octadecanoic acid and linoleic acid. The leaves exhibited a high antioxidant capacity, inhibiting DPPH and ABTS radicals, and the LME showed low inhibition of α-glucosidase enzyme. Conclusions: Palicourea padifolia leaves had a rich composition of cations such as Ca, Na, and Mg. In addition, the LME contained alkaloids, terpenes, lipids, and phenolics, which support the potent antioxidant capacity. In contrast, the LME exhibited a low inhibition of the α-glucosidase enzyme.