Improved water solubility, antioxidant, and sustained-release properties of curcumin through the complexation with soy protein fibrils

Food protein fibrils are progressively recognized as promising matrixes for the preservation and delivery of bioactive compounds. In this study, soy protein fibrils (SPF) formed at 4, 8, and 12 h (80 °C, pH 2.0) were utilized as carriers to complex with curcumin at pH 3.2. SPF with extreme aspect ratios exhibited a higher surface hydrophobicity compared to soy protein isolate (SPI), which improved its ability to form soluble complexes with curcumin. However, a prolonged heating time of 12 h decreased the surface hydrophobicity of SPF since the formation of compact fibrillar aggregates. Further experiments revealed SPF8 (heated for 8 h) had a higher affinity for curcumin, and its predominant interactions were hydrophobic interaction and hydrogen bonding. The curcumin solubility of SPF8-Cur (405.7 μg/mL) significantly enhanced compared to that of SPI-Cur (95.6 μg/mL) at the ratio (protein/fibril to curcumin) of 12.5. The DPPH• and ABTS•+ scavenging capacities of the SPF8-Cur complex were each roughly 1.7 and 2.7 times greater than those of free curcumin. Moreover, SPF8-Cur complex presented excellent antioxidant and outstanding sustained-release properties, further offering opportunities for the release of curcumin in the intestine and improving the bioaccessibility and bioavailability of curcumin.