Surface adsorption of legume proteins upon tryptic hydrolysis: Theoretical and experimental study

The aim of this study was to investigate the effects of enzymatic hydrolysis on surface adsorption of 11S legumin-rich fraction (LR), extracted from pea protein, using a combination of theoretical and experimental approaches. Experimentally, tryptic hydrolysates with 1-12 %degrees of hydrolysis (%DH) were produced at various enzyme to substrate ratios (1:50 to 1:1000 w/w), where moderate degrees of hydrolysis (up to 8 %DH) were found to be abundant in high molecular weight fractions. Tryptic hydrolysis reduced the particle size of LR aggregates from 270 nm to 119 nm and led to a higher degree of disordered structure as confirmed by circular dichroism (CD). Measurements using quartz crystal microbalance with dissipation monitoring (QCM-D), corroborated the observed enhancement in experimentally quantified surface hydrophobicity. Remarkably, we show that a narrow window of hydrolysis (3–8% DH) resulted in an increase in hydrated mass adsorbed on the hydrophobic surface as compared to unhydrolyzed legumin with a higher level of film viscoelasticity in the former. Theoretical Self-Consistent Field (SCF) calculations, involving the most abundant four fragments, demonstrated the relation between the nature of these hydrolysate fragments and surface adsorption. Moderate %DH (3-7%) resulted in a higher number of adsorbed fragments per unit hydrophobic surface area, supporting the QCM-D observations. However, this effect diminished at high %DHs. Findings from this study pinpoint the importance of a moderate degree of hydrolysis in improving surface adsorption behaviour of legume proteins, which might have implications for the design of sustainable plant protein-based formulations.