Optimization of heat-, microwave-assisted and subcritical water extraction of phenolic compounds from ground ivy (Glechoma hederacea L.) using response surface methodology

Abstract This study aimed to optimize heat- (HAE), microwave-assisted (MAE) and subcritical water extraction (SWE) of phenolic compounds from underutilized traditional herb ground ivy (Glechoma hederacea L.) using response surface methodology. Independent variables were extraction time, temperature and sample/solvent ratio, while dependent variables were total phenolic content (TPC) and antioxidant capacity (determined by DPPH and ABTS assays). Extracts obtained under optimum extraction parameters, determined through analysis of the response surface plots and generated mathematical models, were subjected to HPLC-PAD analysis to investigate the presence of individual phenolic compounds. Regardless of the extraction technique, sample solvent ratio 1 g/100 ml resulted in the highest extraction efficiency, while for the same purpose different combinations of temperature and time, depending on the technique, had to be applied - for HAE 100 °C during 10 min, for MAE 90 °C during 4.93 min and for SWE 200 °C during 5.00 min. SWE under optimum parameters yielded extract with the highest TPC (60.1 mg GAE/g dmb) and antioxidant capacity (0.280 and 0.349 mmol Trolox/g dmb) and HPLC analysis revealed formation of new antioxidant that was not detected neither in HAE nor in MAE. On the other side, MAE extract was characterized with the highest content of phenolic compounds characteristic for ground ivy - chlorogenic (1.10 mg/g dmb), cryptochlorogenic (0.59 mg/g dmb), caffeic (0.45 mg/g dmb), rosmarinic (5.56 mg/g dmb) acid and rutin (1.64 mg/g dmb).