Effect of freeze-drying and spray-drying on total phenolics content and antioxidant activity from aqueous extract of justicia secunda leaves

This study aims to evaluate the effect of freeze-drying and spray-drying on total phenolics contents and antioxidant capacity from aqueous extract of Justicia secunda leaves. Total phenolic compounds extraction procedure consists of using an extraction-concentration procedure performed at three-step process, including ultrasound-assisted water extraction followed by cross-flow microfiltration of the crude extract and its concentration by reverse osmosis. After final step of extraction procedure, a concentrated extract, namely RO extract was obtained. In order to convert RO extract to powder form, two drying methods are used; freeze-drying and spray-drying. The powder obtained by freeze drying, namely P1, presented the higher content of polyphenols (9542 ± 38 μmol.g-1 GAE) and antioxidant capacity (4256 ± 15 μmol.g-1 TE) than that obtained by spray drying and namely P2. The freeze-drying technology could be a good outcome to preserve polyphenols structure and consequently their antioxidant capacity in aqueous extract of J. secunda leaves. Moreover, seven minor phenolic compounds of RO extract were characterized by HPLC coupled to UV/Vis diode array detection and mass spectrometry with electrospray ionization (LC/DAD/ESI-MS). There were kaempferol-3-O-coumaroyl glucoside (10), justiflorinol (14), luteolin-7-O-rutinoside (18), apigenin 6-C-glucoside-7-O-rhamnosyl-hexoside (19), quercetin-7-O-glucoside-3-O-rutinoside (20), apigenin-7-O-neohesperidoside (23), and naringenin-7-O-rutinoside (25) among the characterized compounds.