Characterization of egg white gel microstructure and its relationship with pepsin diffusivity

Abstract

Understanding the diffusion of digestive enzymes, particularly pepsin, in different food structures, is a key factor to better control protein digestion and absorption. This study aimed to investigate how protein-based food microstructure impacts pepsin diffusion. Two egg white gels (EWGs) of identical protein concentration (10%) but different structures were used as food models. The two different gel structures were prepared by heating liquid egg white at pH5 and pH9, respectively. Results showed that egg white proteins formed a compact and microstructurally homogeneous gel at pH9 (mean particle size of 0.32 ± 0.02 μm, with a mean interparticle distance of 0.76 ± 0.07 μm), which leads to a lower FITC-pepsin diffusion coefficient (D eff = 44.2 ± 6.1 μm 2 s −1), compared to the pH5-EWG (D eff = 52.5 ± 5.3 μm 2 s −1). The microstructure of the pH5-EWG was characterised by a spatially heterogeneous loose protein matrix made of larger aggregate particles (mean particle size of 0.76 ± 0.07 μm, with a mean interparticle distance of 1.79 ± 0.57 μm). In addition to the effects of the EWG microstructure, the environmental pH also affects the FITC-pepsin diffusion, likely because of the impact on electrostatic interactions between pepsin and the egg white proteins.

Mapping the Spatiotemporal Distribution of Acid and Moisture in Food Structures during Gastric Juice Diffusion Using Hyperspectral Imaging

“…The porous microstructure of the pH 5-EWG may enable diffusion of water as a result of the moisture concentration gradient (Fickian diffusion). As illustrated in Nyemb et al 19 and Somaratne et al, 34 interconnecting empty pores of the pH 5-EWG matrix served as pathways for diffusion of water that enters the egg gel matrix. In contrast to the pH 5-EWG matrix, a complex interplay between the concentration gradient of moisture and the polymer erosion due to acid and pepsin hydrolysis of the protein-gel matrix (non-Fickian diffusion) governed the water diffusion within the pH 9-EWG.…”

“…Article by the compact and dense nature of pH 9-EWG 19,34 and the negligible initial acid content of the pH 9-EWG matrix.…”

“…At pH 5, which is close to the isoelectric point of most egg white protein, the formation of spherical aggregates of egg white protein is predominant which leads to the formation of porous and spatially heterogeneous structures of the pH 5-EWG. 19,34 This loosely packed, more porous, and spatially heterogeneous structure of the pH 5-EWG 19,34 allows the water to diffuse at a faster rate. In contrast, pH 9-EWG has a less porous and a more rigid structure due to the formation of linear aggregates of egg white protein at pH 9, 19,34 which likely hinders the water mobility within the structure.…”

Physical chemistry of gastric digestion of proteins gels

“…The enzyme transport from the gastric juice to the protein gel has to be incorporated in the model. Several studies have already indicated the importance of diffusion of pepsin ( Thevenot et al., 2017 , Qi et al., 2017 , Somaratne et al., 2020 ), and how it is influenced via the protein gel microstructure via obstruction and decrease of free volume ( Axpe et al., 2019 ). The diffusion of pepsin, or fluorescent molecules of similar size, has been compared to several diffusion models, as reviewed by ( Masaro and Zhu, 1999 , Amsden, 2002 ).…”

Role of biochemical and mechanical disintegration on β-carotene release from steamed and fried sweet potatoes during in vitro gastric digestion

“…egg white gels, whey protein gels, dairy gels etc.) on nutrient release during gastric digestion has extensively studied (Guo et al, 2015;Guo, Ye, Lad, Dalgleish, & Singh, 2014;Le Feunteun et al, 2014;Somaratne et al, 2019Somaratne et al, , 2020bSomaratne et al, , 2020c, the mechanism by which the diffusion of the gastric juice affects the mechanical disintegration of natural food matrices (i.e. fruits, vegetables etc.)…”