Intensified soy protein extraction by ultrasound

Abstract

During soymilk production, aqueous extraction conditions are utilised resulting in suboptimal protein extraction yields. This research focuses on the intensification of extraction yields from soybeans using ultrasound and understanding the reasoning behind the results. Milled soybean slurry and okara samples were treated with ultrasound using a lab-scale probe system (20kHz, 400W) for 0, 0.5, 1, 5 and 15min. Ultrasound increased the protein, oil and solids extraction yield from soy slurry by ca. 10% after 1min treatment, especially due to improved solubility and in a less extent to enhanced separation efficiency. Particles in the size range of 2–35μm, corresponding to insoluble protein bodies in the continuous phase, were reduced in frequency but surprisingly not a stepwise decline in size upon ultrasound treatment, as shown by both laser diffraction and confocal laser scanning microscopy. No effects of ultrasound were observed on intact cells present in okara solution and soy slurries. Scanning electron microscopy could not reveal a hypothesised internal organisation of protein bodies within cells, although phytic acid stores were localised which have not been reported before. In conclusion, ultrasound has been identified as a technology with promise in soybean extraction systems where solubility requires improvement.