Use of high-power ultrasound during soy protein production and study of its effect on functional properties of soy protein isolate

Abstract

A comprehensive review focusing on advantages of high-power ultrasound in extraction, emulsification, crystallization, defoaming and modification of functional properties of food proteins was conducted to understand the ultrasonic mechanisms, important process parameters and components to consider for scale-up. The effect of highpower ultrasound on the overall extractability of soy proteins, total sugar, and soy protein isolate yield and functional properties were evaluated. It was hypothesized that the pretreatment of defatted soy flakes with high-power ultrasound prior to soy protein extraction would enhance the extractability of the protein and sugar molecule. Because of the cavitation phenomenon occurring during ultrasound treatment, change in protein native state was expected to occur, which would affect the functional properties of the soy protein isolate. Defatted soy flakes dispersed in water were sonicated for 15, 30, 60 and 120 seconds using a bench-scale ultrasound unit. The ultrasonic amplitude was varied from 0, 21, 42, 63 and 84 μmpp (peak to peak amplitude in μm). The power densities were 0.30, 0.87, 1.53 and 2.56 W/mL representing, very low, low, medium and high-power, respectively. Scanning electron microscopy of sonicated samples showed the structural disruption of soy flakes cell wall. The defatted soy flakes particle size was reduced nearly 10-fold following ultrasonic treatment at high-power settings. Treatment at high-power for 120 seconds gave the highest increase in total sugar release and protein yield, which was of 50 and 46%, respectively, when compared to non-sonicated sample (control). These conditions also gave the highest soy protein isolate yield increase, which was of 34%. To determine effect of temperature increase occurring