Effects of Dual-Frequency Ultrasonic Treatment on Functional and Cryoprotective Properties of Soy Protein Isolate–Curcumin Complexes

The present study investigated the effects of dual-frequency ultrasonic treatment on the functionality of soy protein isolate–curcumin complexes and their cryoprotective properties for beef myofibrillar protein (MP) gel. Control groups were created using pure soy protein isolate (SPI) or SPI-curcumin (SPI-CUR) complex without ultrasonic treatment. Subsequently, SPI underwent modification with various dual-frequency ultrasound frequencies (20/40, 25/40, 28/40 kHz, 15 min, 20 °C) and was then mixed with curcumin (CUR) to fabricate the USP1-CUR, USP2-CUR, and USP3-CUR complexes. Results showed that the USP1-CUR complex achieved the highest encapsulation efficiency (88.41%), loading amount (141.45 µg mg⁻¹ SPI) of curcumin, resulting in the enhancement of emulsifying ability index (19.54 m² g⁻¹) and ABTS scavenging capacity (87.59%), along with improved storage stability, thermal stability, and bioavailability. This finding was corroborated by the cohesive “cluster-like” arrangement and the robust binding between SPI and CUR observed in the USP1-CUR complex through SEM. Moreover, FTIR and XRD analyses elucidated that the interaction between CUR and SPI primarily involves hydrogen bonding and hydrophobic interactions. Furthermore, the incorporation of the USP1-CUR complex exhibited efficient cryoprotection for the MP gel, as evidenced by decreased thawing loss and carbonyl content, enhanced texture properties, and a dense network structure observed throughout freeze-thaw cycles. Molecular docking analysis further demonstrated that incorporating the USP1-CUR complex into MP facilitated the formation of strong hydrogen bonding interactions between curcumin and proteins. In conclusion, SPI subjected to rational dual-frequency ultrasound can improve the delivery efficiency of CUR and provide valuable insights for utilizing the functional complex of plant proteins and polyphenols to reduce freeze-thaw damage in meat production.