Ultrasonic-Assisted Fabrication and Stability Evaluation of Pepper Seed Protein Nanoemulsions

Pepper seeds, a key byproduct of pepper processing, are rich in high-quality plant proteins. This study investigated the structural and functional properties of pepper seed protein isolate (PSPI) and optimized the ultrasonic homogenization process for PSPI-based nanoemulsions using response surface methodology (RSM), followed by stability evaluation. The results showed that glutamic acid is the dominant amino acid in PSPI, with a molecular weight range of 10-55 kDa. Some protein subunits were interconnected via disulfide bonds. Functionally, PSPI had lower water-/oil-holding capacities but superior emulsifying activity compared to soy protein isolate (SPI). RSM optimization determined the optimal nanoemulsion parameters within experimental constraints: PSPI 0.53%, ultrasonic power 500 W, and ultrasonic time 130 s, yielding a nanoemulsion with a droplet size of 319 ± 2 nm, consistent with the theoretical prediction (318 nm). The nanoemulsion demonstrated stability under neutral-to-alkaline conditions (pH 7.0-9.0), high ionic strength (Na⁺ concentration ≤ 100 mM), and elevated temperatures (40-100 °C), without phase separation or aggregation. This work supports pepper seed protein utilization and provides insights for plant protein nanoemulsion production.