Extraction of Polyphenolic Compounds from Eucalyptus globulus Bark: Process Optimization and Screening for Biological Activity

The bark of Eucalyptus globulus is a promising source of polyphenolic compounds that could be extracted employing polar solvents. Extraction experiments were planned according to the Box–Behnken design to evaluate the effect of temperature and time of extraction and the ethanol/water ratio on the dependent variables total phenolic content (TPC; as gallic acid equivalents, GAE), antioxidant activity (AA; as millimoles of ascorbic acid equivalents, AAE), proanthocyanidins (Pac; as mimosa extract equivalents, MEE), Stiasny number (SN), and coextracted total carbohydrates (TC). Response surface models were developed, and statistical analysis of variance was performed. A maximum of TPC of 32% (w GAE /w extract ) was achieved for 264 min, 82.5 °C, and 52% ethanol corresponding to about 2% of the bark weight. These conditions are close to those leading to maximum values of compounds with AA (2.1 mmol AAE /g extract ) and Pac 14% (w MEE /w extract ). TC in the extract and the SN predicted were 22.7% (w TC /w extract ) and 37, respectively. Preliminary studies concerning the biological activity of some extracts have demonstrated their differential capacity to reduce human breast cancer cell proliferation.