Co-Encapsulation of Curcumin and Diosmetin in Nanoparticles Formed by Plant-Food-Protein Interaction Using a pH-Driven Method

In this work, a pH-driven method was used to prepare zein–soy protein isolate (SPI) composite nanoparticles (NPs). The mass ratio of SPI to zein influenced the Z-average size (Z-ave). Once the zeta potential stabilized, SPI was completely coated on the periphery of the zein NPs. The optimal mass ratio of zein:SPI was found to be 2:3. After determining the structure using TEM, curcumin (Cur) and/or diosmetin (Dio) were loaded into zein–SPI NPs for co-encapsulation or individual delivery. The co-encapsulation of Cur and Dio altered their protein conformations, and both Cur and Dio transformed from a crystalline structure to an amorphous form. The protein conformation change increased the number of binding sites between Dio and zein NPs. As a result, the encapsulation efficiency (EE%) of Dio improved from 43.07% to 73.41%, and thereby increased the loading efficiency (LE%) of zein-SPI NPs to 16.54%. Compared to Dio-loaded zein–SPI NPs, Cur/Dio-loaded zein–SPI NPs improved the storage stability of Dio from 61.96% to 82.41% within four weeks. The extended release of bioactive substances in the intestine during simulated gastrointestinal digestion improved the bioavailability. When exposed to a concentration of 0–800 µg/mL blank-loaded zein–SPI NPs, the viability of HepG2 and LO-2 cells was more than 90%, as shown in MTT assay tests. The zein–SPI NPs are non-toxic, biocompatible, and have potential applications in the food industry.