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

Abstract

<p>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 high-power 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 ym). 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 during sonication, the ultrasonic pretreatment of the defatted soy flakes was carried out with and without temperature moderation.</p> <p>The heat generated during sonication had no significant effect on protein and sugar release from defatted soy flakes. Functionality of soy protein isolate obtained from defatted soy flakes treated for 30, 60 and 120 seconds at 0.30 and 2.56 W/mL was assessed. The sonication power and the sonication time both impacted significantly the soy protein isolate functional properties. The sonication of defatted soy flakes for 120 seconds at the high-power level improved the soy protein isolate solubility by 34% at pH 7.0, while decreasing emulsification and foaming capacities by 12 and 26%, respectively, when compared to soy protein isolate obtained from untreated defatted soy flakes. Rheological behavior of the soy protein isolate was also modified with significant loss in consistency coefficient due to sonication. Some of these results could be explained by the loss of the protein native state with increased sonication time and power.</p>