The aim of this study was to evaluate the most effective extraction condition (temperature, solvent type and time) for recovery of high-value phytochemicals present in the Tabernaemontana catharinensis leaves (TC) and to assess their effect on biochemical parameters in streptozotocin-induced diabetic rats. The extraction of phenolic compounds from TC using a factorial design (FD) 2³, high performance liquid chromatography (HPLC), response surface methodology (RSM) and principal component analysis (PCA) were studied. It was found that the optimal conditions for extraction of phenolics were higher temperature (65 °C) and time (60 min) using ethanol as extractor solvent. In this condition of extraction (A8), total phenolic compounds (TPC) and antioxidant activity (AA) were determined. Additionally, this extract was used to evaluate their effect on antioxidant enzyme activities (superoxide dismutase (SOD) and catalase (CAT)) as well as lipid peroxidation (LP) and protein thiols level (PSH) in the liver and kidneys of normal and diabetic rats. As result, T. catharinensis extract presented TPC content of 23.34 mg EAG/g (equivalent gallic acid) and AA of 34.26 μmol Trolox/g. Phenolic acids (ferulic acid and coumaric acid) and flavonoids (quercetin, rutin and pinocembrin) could be recovered and identified by HPLC. This study indicated an important role of the T. catharinensis extract on free radical inactivation and on the antioxidant defense system in diabetic rats. In fact, the use of T. catharinensis extract restored the normal activity of SOD (p < 0.05) and suppressed malondialdehyde levels in liver and kidney tissues. Thus, the T. catharinensis extract, rich in phenolic compounds, can be responsible for the recover the enzymatic changes in the liver and kidney tissues provoked by diabetes in rats. In addition, the lipid peroxidation rate decreased in the diabetic rats treated with T. catharinensis.

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The açaí is a popular Brazilian fruit, however, already part of the world's healthy eating habits owing to its antioxidant properties. The study aimed to determine the effect of solvent in extracting phenolic compounds with antioxidant potential in açaí juçara (Euterpe edulis Mart.) using a Completely Randomized Design (CRD). The phenolic compound profile was quantified by High-Performance Liquid Chromatography (HPLC), and the data set was analyzed by Principal Component Analysis (PCA). The PCA was applied to evidence the relationships between the concentration of phenolic compounds and the solvents. Furthermore, the antioxidant activity was also determined by 2,2’-diphenyl-1-picrylhydrazyl (DPPH), 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and Ferric Reducing Antioxidant Power (FRAP) methods. The solvent ethanol: water 70% was more efficient in extracting phenolic compounds with high antioxidant activity. In this extract, salicylic acid was found in high concentrations as well as catechin, epicatechin, and coumaric acid. Based on a consensus that phenolic compounds are associated with the most powerful antioxidant activities of fruits, the “açaí juçara” from the Atlantic Forest is a potential source of polyphenols. They could be used as natural antioxidants for application in the food and pharmaceutical industry in order to substitute the synthetic antioxidants.