Curcumin (Cur) exhibits potential as a food preservative because of its natural antibacterial and antioxidant properties. Nevertheless, its practical application is challenging due to poor water solubility and physicochemical instability. In this study, we prepared Cur-loaded protein nanoparticles (RCs) with a high loading capacity. The water-dispersible nanoparticles (10–30 nm) enclosing Cur with a loading capacity of up to 302 mg/g protein were formed by neutralizing rice proteins (RPs) from alkali-unfolded RPs utilizing cation exchange resin in the presence of Cur. Compared to free Cur, RCs improved the heat-stability and photo-stability of Cur by 26.7% and 23.2%, respectively. The RCs demonstrated significantly higher antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) compared to free Cur, with inhibition rates exceeding 94.45% and 91.00%, respectively. Additionally, RCs exhibited superior antioxidant activities across multiple assays, with RCs5 showing increases of 122.22% (DPPH), 64.99% (ABTS), and 94.72% (FRAP) compared to free curcumin. RCs significantly preserved freshly-cut apples, with the RCs5 group showing the lowest bacterial count (1.46 log CFU/g) and the highest total soluble solid content (10.45%) after 7 days of storage. RCs also reduced weight loss to 34.35% of the control and effectively minimized browning by at least 5.83% compared to the control group. These findings highlight the potential use of RCs to improve the antimicrobial and antioxidant activities of encapsulated phytochemicals, which may have numerous applications in, for example, food preservations.