Protein glutaminase-mediated deamidation enables soy protein isolate to act as a stable zinc carrier with improved gastrointestinal bioaccessibility.

Abstract

Poor gastrointestinal bioaccessibility limits the efficacy of conventional Zn supplements. Herein, protein glutaminase-mediated deamidation of soy protein isolate (SPI) was performed to develop a Zn delivery system. Deamidation increased the Zn-binding capacity of SPI to 29.8 mg/g protein through the formation of additional carboxyl-containing groups. Structural analyses of Zn-chelated proteins (ZCPs) revealed conformational changes characterized by reduced α-helix content, altered tertiary structure, increased surface hydrophobicity, and an increase in negative surface charges. These changes improved the antioxidant activity of the system and increased its foaming and water-holding capacities by 97.0% and 98.2%, respectively, while decreasing its emulsifying activity. During simulated gastrointestinal digestion, the SPI-Zn system exhibited higher Zn solubility than Zn sulfate and Zn gluconate, resulting in a 78.8% increase in bioaccessible Zn content. Overall, deamidation enhanced the Zn-binding capacity and gastrointestinal stability of SPI and improved Zn bioaccessibility, highlighting its potential for developing protein-based Zn fortification systems.