Effects of NaCl and CaCl₂ on the Growth Process and Morphology of Soy Protein Isolate Fibrils

To explore effects of common metal chlorides (NaCl and CaCl₂) in food system on the growth process and morphology of soy protein isolate (SPI) fibrils. The SPI fibrillation was induced by the acid-heat treatment (pH2, 85 ℃) in the presence of NaCl and CaCl₂ to prepare soy protein isolate fibrils (SPIF). The addition of NaCl and CaCl₂ significantly increased the Th T fluorescence intensity of SPIF at the maturity phase, with their primary nucleation rates reaching 3.29×10¹⁰ and 4.12×10¹⁰ mol⁻²·h⁻², respectively. In the initial stage of fibrillation (0~4 h), NaCl and CaCl₂ promoted the hydrolysis of α, α’ and β subunits of SPI, and their surface hydrophobicities increased to 5.1×10⁷ and 5.7×10⁷ respectively, and the free sulfhydryl contenr in SPI induced by CaCl₂ increased significantly to 24.5 μmol/L (P<0.05). In the middle and late stages of fibrillation (4~24 h), the average particle sizes of SPI induced by NaCl and CaCl₂ increased significantly (P<0.05), reaching 6008 and 5930 nm, respectively. In the mature SPIF (24 h), antiparallel/parallel β-sheet ratios were 7.16 and 1.59, respectively. The results showed that the addition of NaCl and CaCl₂ promoted the hydrolysis of SPI and the formation of nucleation monomers during fibrillation process, increased the primary nucleation rate of SPI fibrillation, promoted the formation of SPIF, and had a regulatory effect on the morphology of SPIF, making it form larger clustered fibril aggregates. In addition, compared with NaCl, CaCl₂ had a more significant effect on promoting the growth process and regulating the morphology of SPIF. This study provides a certain theoretical basis for the controllable regulation and application of SPIF in food system.