Effects of protein concentration during ultrasonic processing on physicochemical properties and techno-functionality of plant food proteins

Plant proteins have been increasingly recognized as very relevant food ingredients, due to concerns related to ecology, health and even religion. However, compared to food proteins from animal sources, the former ones have considerably lower dispersibility. Because of this, exploring techno-functional properties of plant proteins in formulations is much more difficult. Ultrasound has been explored in food processing for different purposes and represents a strategic non-thermal operation to enhance the dispersibility (and, consequently, several techno-functionalities) of food proteins. During ultrasonic processing in aqueous medium, the concentration of protein material may favour or impair the action of ultrasound waves, but this fact has been only marginally addressed in literature. Hence, this study investigated the effects of different protein concentrations during ultrasonic processing on techno-functional properties of soy protein isolate (SPI), rice protein isolate (RPI), and pea protein concentrate (PPC). Ultrasonic treatments (USt) at 20 kHz were designed using a Box–Behnken experimental planning, varying ultrasound power (562.5, 637.5 or 712.5 W), application time (120, 360 or 600 s), and concentration of the proteins in aqueous medium [1.0%, 3.0% or 5.0% (w/v)]. Hydrophobic surface index (H0), molecular mass profile, hydrodynamic diameter (dh), and ζ-potential of these three protein materials after USt were evaluated and discussed. Moreover, Response surface methodology was applied to evaluate and to optimize the following techno-functionalities of SPI, RPI, and PPC: water and oil holding capacity (WHC and OHC), and foaming, emulsifying, and gelling properties. After USt, OHC increased for the three protein materials. For SPI, dispersibility and FC at 712,5 W | 600 s | 1.0 % w/v were improved. The WHC (562.5 W | 120 s | 5.0 % w/v), OHC (562,5 W | 120 s | 1.0 % w/v) of SPI were also increased. For PPC, USt led to enhanced dispersibility (712.5 W | 360 s | 3.0 % w/v), WHC (712.5 W | 600 s | 5.0 % w/v), OHC (637,5 W | 120 s | 3.0 % w/v). On the other hand, none of the USt was efficient to significantly modify neither physicochemical nor techno-functional properties of RPI, which remains a challenge. In summary, the present study showed that USt may effectively improve the technological functionality of SPI and PPC. However, concentrations of these protein materials should be kept < 5% (w/v) during ultrasonic processing, otherwise the ultrasound wave