Esterified Soy Proteins with Enhanced Antibacterial Properties for the Stabilization of Nano-Emulsions under Acidic Conditions

Abstract

Soy protein isolate (SPI), including β-conglycinin (7S) and glycinin (11S), generally have low solubility under weakly acidic conditions due to the pH closed to their isoelectric points (pIs), which has limited their application in acidic emulsions. Changing protein pI through modification by esterification could be a feasible way to solve this problem. This study aimed to obtain stable nano-emulsion with antibacterial properties under weakly acidic conditions by changing the pI of soy protein emulsifiers. Herein, the esterified soy protein isolate (MSPI), esterified β-conglycinin (M7S), and esterified glycinin (M11S) proteins were prepared. Then, pI, turbidimetric titration, Fourier transform infrared (FTIR) spectra, intrinsic fluorescence spectra, and emulsifying capacity of esterified protein were discussed. The droplet size, the ζ-potential, the stability, and the antibacterial properties of the esterified protein nano-emulsion were analyzed. The results revealed that the esterified proteins MSPI, M7S, and M11S had pIs, which were measured by ζ-potentials, as pH 10.4, 10.3, and 9.0, respectively, as compared to native proteins. All esterified-protein nano-emulsion samples showed a small mean particle size and good stability under weakly acidic conditions (pH 5.0), which was near the original pI of the soy protein. Moreover, the antibacterial experiments showed that the esterified protein-based nano-emulsion had an inhibitory effect on bacteria at pH 5.0.

Development of Eco-Friendly Soy Protein Fiber: A Comprehensive Critical Review and Prospects

“…Esterification of soy proteins can elevate their isoelectric point to 8 from 4.5 [80]. Ethanol-esterified soy proteins acquire positive charges in weakly acidic environments, which helps curtail the growth of bacteria with negatively charged cell membranes [81].…”

Proteins from Legumes, Cereals, and Pseudo-Cereals: Composition, Modification, Bioactivities, and Applications

“…Additionally, the emulsification and foaming properties of these esterified pulse proteins in the acidic pH range of 2.0 to 6.0 surpassed those of the native proteins. Wang et al [52] found that altering the protein isoelectric point (pI) through esterification could be a feasible way to enhance these properties. All esterified-protein nano-emulsion samples exhibited small mean particle sizes, good stability, and an antibacterial-inhibitory effect under weakly acidic conditions (pH 5.0).…”