High-power ultrasound as pre-treatment in different stages of soymilk manufacturing process to increase the isoflavone content

Ultrasound (US) was applied as a pre-treatment in hydrated soybeans (HSB) and soybean slurry (SBS) during soymilk elaboration process to evaluate the feasibility of increasing the isoflavone content (IC) in the resultant soymilk. A predictive model and optimum US processing conditions were obtained by response surface methodology (RSM) using a three-level-three-factor Box-Behnken statistical design (BBD) in which US amplitude (50, 75, and 100%), temperature (30, 45, and 60 °C), and time (20, 40, and 60 min) were selected as independent variables. Most of the US treatments applied in the HSB or SBS caused a significant increase (3-62%) in the total IC of the obtained soymilks over the control soymilk (6.97 mg/100 mL). However, the IC of the resultant soymilks from sonicated HSB (11.38 mg/100 mL) was significantly higher than that in soymilk prepared from US-treated SBS (8.66 mg/100 mL). Experimental data were fitted into a 2nd-order-polynomial model and processing parameters were optimized (100% amplitude, 30 °C, 20 min) to get the highest predicted and experimental IC, 11.38 and 12.8 mg/100 mL, respectively. These results indicated that US is a potential technology that could be implemented during soymilk manufacturing processing as pre-treatment of HSB to obtain soymilk with high isoflavone content and consequently better functionality.