Effect of ultrasound and microwave processing on the structure, in-vitro digestibility and trypsin inhibitor activity of soymilk proteins

Abstract

Soymilk is becoming popular worldwide due to its nutritional benefits and the increasing demand for plant-based alternatives for cow's milk resulting from lactose intolerance and dairy allergy. However, soymilk proteins have a lower digestibility and contain higher anti-nutrients compared to dairy proteins. In the present study, ultrasound (25 kHz, 400 W, 1–16 min) and microwave (2450 MHz, 70–100 °C, 2–10 min) treatment were applied to evaluate the relationship between conformational changes and in vitro protein digestibility (IVPD) of soymilk proteins as well as the changes of trypsin inhibitors activity. The results revealed that ultrasonication significantly reduced trypsin inhibitor activity up to 52% and improved the digestibility of proteins in soymilk. The digestibility of soymilk significantly increased up to 93% after 10-min microwave processing at 85 °C compared to the untreated samples. Further, a significant loss in α-helix and an increase of β-sheet in the soymilk proteins was observed in ultrasound (16 min) and microwave treatments at 85 °C. The findings of this study demonstrate that ultrasonication and microwave processing showed potential applications in the reduction of trypsin inhibitors activity and improving the digestibility of soymilk through changing the secondary structures of related proteins.