Simultaneous extraction of oil and soy isoflavones from soy sauce residue using ultrasonic-assisted two-phase solvent extraction technology

• Ultrasonic-assisted two-phase solvent extraction technology was applied.
• Response surface methodology was used to optimize key extraction factors.
• The extracted oil could be a potential raw material for biodiesel production.
• The extracted soy isoflavones existed mainly in aglycones form.

Simultaneous extraction of oil and soy isoflavones from soy sauce residue (SSR) was investigated by means of the two-phase solvent extraction intensified by ultrasonication. A single factor test was first carried out to study the effects of ultrasonic time, ethanol concentration, ratio of ethanol/water phase to raw material, ratio of hexane phase to raw material, and ultrasonic power on the extraction rates of oil and isoflavones, then response surface methodology was applied to further optimize and simulate four key factors. The results showed that the extraction rates of oil and isoflavones of 92.07% and 92.53%, respectively, could be obtained when ethanol concentration was 74.88%, ratio of ethanol/water phase to raw material 15:1, ratio of hexane phase to raw material 8.64:1, extraction time 20 min, and ultrasonic power 160 W. The predictive rates were well matched with the experimental ones. The quality analysis of oil and soy isoflavones from SSR showed that the extracted oil with high acid value could be a potential raw material for biodiesel production instead of cooking. The extracted soy isoflavones existed mainly in aglycones form, which might afford higher bioactivity than that from the other soybean products.