Pepsin diffusivity in whey protein gels and its effect on gastric digestion

Abstract

Protein is essential to human health, but its digestion kinetics in varied structures are not yet well understood. We previously found different kinetics of protein hydrolysis in solution and in gels, and we hypothesized that the difference stemmed from the steric hindrance of gel structure to the diffusion of pepsin and its hydrolysates. To better understand the pepsin diffusivity in food matrices and its effect on digestion, we determined the diffusivity of pepsin in water and in whey protein isolate (WPI) gels by fluorescence correlation spectroscopy (FCS).We estimated the pepsin concentration gradient during digestion based on the determined diffusivity, which showed that the pepsin is constrained within a thin layer from the gel surface. Gel composition analysis confirmed this constraint: peptides as protein fragments were observed only in the first 2 mm of the WPI gels after 6 h of in vitro gastric digestion. Scanning electron microscopy indicated that pepsin loosened the microstructure of whey protein gel surfaces, which may accelerate pepsin diffusion and consequently gel surface disintegration. We conclude that the mode of whey protein gel digestion is determined by the summed effect of diffusion limitation, hydrolysis rate and microstructure transformation.

Overcoming in vitro gastric destabilisation of emulsion droplets using emulsion microgel particles for targeted intestinal release of fatty acids

“…From Figure 3A and B (lines a and a'), after 120 min in SGF 51% of -lactoglobulin and 92% oflactoglobulin remained as compared to the non-digested whey protein solution. Due to the globular nature of -lactoglobulin, pepsin has very limited access to the carboxyl side of the aromatic amino acid buried inside the -lactoglobulin dimers (Guo, et al, 1995;Luo, Borst, Westphal, Boom, & Janssen, 2017;Nacer S, et al, 2004).…”

“…2.3 nm (Amsden, 1998), so pepsin would more easily diffuse into the larger WPI microgel particle pores, resulting in a higher digestibility. In the case of the emulsion microgel particles, pepsin might only be able to digest a thin layer of WPI at the surface of the particles (Luo, Boom, & Janssen, 2015;Luo, et al, 2017). The tortuous network of the droplets within the emulsion microgel particles might also hinder pepsin reaching the interfacial whey protein of all the droplets.…”

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

“…Digestion of food protein initiates in the stomach by the action of pepsin (Akimov & Bezuglov, 2012;Inglingstad et al, 2010). The mobility of pepsin into food matrices and their subsequent breakdown in the gastric environment are strongly correlated with the food matrix structure (Guo et al, 2015;Luo, Borst, Westphal, Boom, & Janssen, 2017;Nyemb, Guérin-Dubiard, et al, 2016;Thevenot, Cauty, Legland, Dupont, & Floury, 2017). Since food structure can have a critical role in determining the rate of peptide release in the stomach and absorption of amino acids/peptides in the small intestine, it is of ultimate importance to nutrition and health (Lorieau et al, 2018;Luo et al, 2017;Nyemb, Causeur, et al, 2016;Nyemb, Guérin-Dubiard, et al, 2016).…”

“…It has recently been used to study the mobility of the digestive enzymes within the food matrix (Guo, Bellissimo, & Rousseau, 2017;Thevenot et al, 2017). Techniques related to confocal microscopy including FRAP and fluorescence correlation spectroscopy (FCS) have been used to characterize the diffusion of pepsin in different dairy-based gel microstructures (Luo et al, 2017;Thevenot et al, 2017). Luo et al (2017) have shown that the architecture of the dairy-based gel matrix could affect the overall proteolysis reaction rate and the gels breakdown properties.…”

Pre-treatment and digestion of plant proteins - The quinoa case

“…Malting can improve amaranth protein digestibility (Hejazi et al, 2016). Conversely, extended toasting times have a negative effect on the rate of protein hydrolysis of rapeseed meal (Salazar-Villanea et al, 2017), and matrices formed with a prior heat treatment such as whey protein isolate gels hinder the diffusion of pepsin and limit its hydrolytic activity (Luo et al, 2017). determined that the in vitro gastric digestibility of quinoa protein extracts was reduced upon heating.…”