Effect of high intensity ultrasound on physicochemical and functional properties of soybean glycinin at different ionic strengths

In this work, soybean glycinin was treated by high intensity ultrasound (HIU; 20 kHz at 80 W cm(-2) from 0 to 40 min) in three ionic strengths (I = 0.06, 0.2 and 0.6) at pH 7.0. At all three ionic strengths, HIU of glycinin increased emulsion stability and decreased the turbidity. However, the effects of HIU on the particle size, particle distribution, solubility, emulsifying activity index, and surface hydrophobicity showed different characteristics in three ionic strengths. For example, after HIU, surface hydrophobicity of glycinin increased at I = 0.06 and 0.2, but remained unchanged at I = 0.6. The effects of HIU on glycinin were more pronounced at I = 0.2 than the other two ionic strengths. Furthermore, HIU influenced the glycinin aggregates, but remained the secondary and tertiary structures almost unchanged, which could be demonstrated by circular dichroism and the intrinsic fluorescence spectra. Industrial relevance: Soy protein is a plant protein which is widely employed in food products due to its high nutritional value, low price as well as its good functional properties. However, soy protein, especially glycinin, is easy to form aggregates and therefore limits soy proteins'application in some aspects. High intensity ultrasound (HIU) waves are generally considered as safe, non-toxic, and environmentally friendly. The results of this study suggested that HIU could dissociate soy glycinin and improve some functional properties of soybean glycinin, indicating that HIU can be considered as a potential tool to change soy glycinin's functional property. Moreover, this work found that the effects of HIU on physicochemical and functional properties of soybean glycinin were different in three ionic strengths, which could provide some fundamental information on how HIU influences the soy glycinin structures in different ionic strength and increase the application of HIU in the soy bean industry. (C) 2016 Elsevier Ltd. All rights reserved.