A novel insight into the binding behavior between soy protein and homologous ketones: Perspective from steric effect

Abstract

The binding behavior between soy protein isolate (SPI) and homologous ketones was examined in this study. Three ketones (2-hexanone, 2-heptanone, and 2-octanone) with different carbon chain lengths were selected to investigate the interaction mechanism between SPI and ketones, and three ketones with positional isomers, namely 2-nonanone, 3-nonanone, and 4-nonanone, were used to construct different steric effect. Ultraviolet, fluorescence, and circular dichroism results showed that ketones induced the conformational perturbations of SPI, weakening the polarity of the environment in which the chromogenic group was located and triggering the quenching of SPI intrinsic fluorescence. Hydrophobic site competition experiments revealed that the presence of steric hindrance hindered the collision of compounds with SPI active site. The optimal binding locus for ketones within the SPI structure was determined by molecular docking, and two key amino acids, LYS412 and ASN484, were found. The calculated binding energy (-25.682 ∼ -17.952 kcal mol−1) and steric energy (7.883 ∼ 14.894 kcal mol−1) of ketones showed that steric effects played a negative role in the binding of SPI to flavor compounds, but this role was weaker than hydrophobic interactions and hydrogen bonding. The improved understanding of the role of carbon chain lengths and steric hindrance on ketone retention could support the flavor product designer or scientists to optimize flavor retention and delivery.