Novel Protein Hydrocolloids Constructed by Hydrophobic Rice Proteins and Walnut Proteins as Loading Platforms for Nutraceutical Models

Low water solubility strictly limits the application potential of such plant-derived proteins as rice proteins (RPs) and walnut proteins (WPs), albeit their nutritional and health-related properties. In this study, by simply dissolving RPs and WPs at pH 12 prior to neutralization, we successfully prepared nanoscale hydrocolloidal composites with shared internal molecular arrangements, boosting the solubility of RPs to over 80% (w/v) while completely solubilizing WPs. Atomic force microscopy and transmission electron microscopy showed that the two polypeptide chains were packed into homogeneous particles with a diameter ranging from 50 to 100 nm. Varying the mass ratio of RPs/WPs enabled the flexible or rigid chain configuration, which was confirmed by static and dynamic light scattering. The results from zeta-potential and surface hydrophobicity demonstrated that the burial of hydrophobic groups and the exposure of charged moieties stipulated the aqueous stability of the protein composites. The apigenin encapsulated in protein composites showed preferable aqueous solubility. Moreover, the improvement of bioaccessibility of apigenin was proved by in vitro simulated digestion experiment. This study provided a new route for utilizing underdeveloped protein resources, especially those with hydrophobic attributes, and potentially expanding the applications of these proteins in the fields of food and related areas.