Ultrasound‒treated soy protein fibrils: A potential vehicle for curcumin with improved water solubility, antioxidant activity and sustained‒release property

Plant protein fibrils have recently attracted considerable attention as delivery vehicles for hydrophobic bioactive compounds. In this work, ultrasound treatment was applied to improve the structure of protein fibrils. The aim of this work was to investigate the impacts of ultrasound treatment on the structure of soy protein fibrils (SPF), and further explore the interaction between ultrasound‒treated SPF (USPF) and curcumin (Cur) to clarify the impacts of ultrasound on SPF as delivery vehicles. Thioflavin T fluorescence, SDS‒PAGE, Fourier transform infrared (FTIR) spectroscopy, and far‒UV circular dichroism spectroscopy revealed no significant changes in the primary and secondary structure of SPF after ultrasound treatment. Compared with SPF, USPF presented a more uniform particle size and higher surface hydrophobicity. Fluorescence quenching, ultraviolet–visible spectroscopy, isothermal titration calorimetry, and FTIR spectroscopy indicated USPF10 (ultrasonication for 10 min) possessed a high affinity toward curcumin via hydrophobic interactions and hydrogen bonds. The curcumin solubility in USPF10-Cur (133.19 μg/mL) complex was much higher than SPI-Cur (78.26 μg/mL) and SPF-Cur (116.22 μg/mL) complexes. The USPF10‒Cur complex exhibited good colloidal stability and thermal stability. The DPPH and ABTS scavenging capacities of the USPF10‒Cur complex were approximately 1.4 and 2.7 folds higher than those of free curcumin, respectively. An In vitro digestion assay suggested that the USPF10‒Cur complex showed a much more stable and sustainable release of curcumin and provided chances for curcumin release in the intestine. This study indicated that USPF might be promising delivery vehicles for hydrophobic bioactives as stable and functional ingredients in acidic food systems.