High-power ultrasonication-assisted extraction of soybean isoflavones and effect of toasting

Abstract

The effect of high-power ultrasonication (HPU) on extraction of soybean isoflavones and components, including total phenolic and DPPH radical scavenging activities (RSA) were evaluated. Isoflavones from defatted soybean flakes were extracted using a bench scale HPU system at 20 kHz and varying amplitudes (18–54 μm) for 1 and 3 min. Aqueous acetonitrile, and aqueous ethanol based solvents were evaluated for extraction at samples-to-solvent ratios of 0.1:1 and 0.2:1. The non-sonication control extraction was with mixing with magnetic stirrer for 2 h. Preliminary data indicated 1.2–1.5 times more genistein recovery at 1, and 3 min sonication compared to control, however, total phenolic decreased. The genistein recovery was lower at higher sonication levels. RSA also decreased to 40% for HPU-assisted extractions. Total isoflavones recovery in HPU-assisted extractions increased from 600 to 5813 μg/g. The concentration of major isoflavone components, genistein, daidzein, and glycitein also increased by 10-fold. HPU for 3 min reduced the average particle size of treated soy flakes from 530 μm to 60 μm. Toasting at 150 °C of defatted soy flake for longer period of time led to higher aglycone concentration in extract; however, 2 h toasting was sufficient prior to HPU-assisted extraction.