Effects of ultrasound treatment on structural and functional properties of radish seed protein

Dried radish seed is a traditional Chinese herbal medicine that is rich in oil and protein. Radish seed meal, which is a byproduct of oil production, is high in protein (30%-35%). In order to develop a novel plant protein with excellent functional properties, this study investigated the effects of ultrasound treatment (20 kHz, amplitude of 40%, 0-10 min) on the physicochemical, functional, and antioxidant properties of radish seed protein (RSP) extracted from radish seed meal. The molecular weight of RSPs was 11-75 kDa. Ultrasonic treatments at 2-10 min reduced the particle size, narrowed the size distribution, and increased the surface negative charge of RSP. RSP solubility increased from 77.69% ± 0.69% to 88.50% ± 1.36% after ultrasound treatment for 10 min, resulting in optimal foaming and emulsifying properties of RSP. However, the foam stability of RSP decreased after sonication for 10 min. By contrast, the antioxidant activities of RSP increased significantly with extended sonication duration. Although sodium dodecyl sulfate-polyacrylamide gel electrophoresis results showed that sonication had few effects on RSP digestibility, the antioxidant capacities of the digested products during simulated intestinal digestion were enhanced, indicating RSP to be a good resource of antioxidant peptides. These results provide a fundamental basis for the use of ultrasound to enhance the functional and antioxidant abilities of RSP, promoting its application in food industry and the bioactive peptide field.