Effect of Ca²⁺-Transglutaminase Crosslinking on Gel Characteristics and Vitamin D₃-Loading Capacity of Soy Protein Isolate Emulsion

In this study, the effect of transglutaminase (TGase)-Ca²⁺ crosslinking on the texture, water-holding capacity (WHC), rheological properties, and vitamin D₃ (VD₃)-loading capacity of soy protein isolate (SPI) emulsion gels was investigated. The results showed that with increasing SPI concentration (4%-12%), Ca²⁺ concentration (0-30 mmol/L) and TGase dosage (0-90 U), the hardness, elasticity, WHC and rheological properties of SPI emulsion gels first increased and then decreased or leveled off. Upon the addition of 10% SPI, 10 mmol/L Ca²⁺ and 30 U of TGase, the best gel characteristics were obtained. The emulsion gel prepared by TGase-Ca²⁺ crosslinking showed a denser microstructure and more uniform oil droplet distribution as observed by confocal laser scanning microscopy (CLSM). The results of in vitro simulated digestion showed that compared with free VD₃, its mixture with medium chain triglycerides (MCT), and SPI emulsionencapsulated VD₃, SPI emulsion gel-encapsulated VD₃ showed reduced release rate of free fatty acids (FFAs) and increased bioaccessibility of VD₃. The results of this study provide a theoretical basis for the preparation of protein supplements and the application of hydrophobicity-enhancing substances in functional foods.