Probe diffusion in phase-separated bicontinuous biopolymer gels

Abstract

Probe diffusion was determined in phase separated bicontinuous gels prepared by acid-induced gelation of the whey protein isolate-gellan gum system. The topological characterization of the phase-separated gel systems is achieved by confocal microscopy and the diffusion measurements are performed using pulsed field gradient (PFG) NMR and fluorescence recovery after photo-bleaching (FRAP). These two techniques gave complementary information about the mass transport at different time- and length scales, PFG NMR provided global diffusion rates in the gel systems, while FRAP enabled the measurements of diffusion in different phases of the phase-separated gels. The results revealed that the phase-separated gel with the largest characteristic wavelength had the fastest diffusion coefficient, while the gel with smaller microstructures had a slower probe diffusion rate. By using the diffusion data obtained by FRAP and the structural data from confocal microscopy, modelling through the lattice-Boltzmann framework was carried out to simulate the global diffusion and verify the validity of the experimental measurements. With this approach it was found that discrepancies between the two experimental techniques can be rationalized in terms of probe distribution between the different phases of the system. The combination of different techniques allowed the determination of diffusion in a phase-separated biopolymer gel and gave a clearer picture of this complex system. We also illustrate the difficulties that can arise if precautions are not taken to understand the system-probe interactions.

Methods for investigation of diffusion processes and biopolymer physics in food gels

“…Within nanopores (<150 nm) the mass transport is dominated by diffusion, in bigger pores in the range of some mm by convective flow [20 ]. A certain influence on mass transport within gels has also obstruction, friction and special interactions between solute and gel, for instance electrostatic interactions [21,22].…”

Pore size effects on convective flow and diffusion through nanoporous silica gels

“…Earlier studies on the transport properties for water of different protein gels as a function of pH, temperature and ionic strength suggests that materials with pore widths in the range from approximately 200 nm and up to 2m are more predisposed to lose moisture compared to materials with pores on an even smaller length scale [13][14][15][16]. The mass transport through silica gels [3,17] and other porous soft materials [1,2,18] have been recently and previously studied. However, nanoscale correlation between pore sizes and water transport has not earlier been visualised and quantified experimentally, on a length scale less than 100 nm.…”

“…The research topic of soft porous colloidal materials is very current for direct industrial applications as well as basic research [1][2][3]. These kinds of materials are already abundantly used in everyday applications such as food, pharmaceuticals [4], chromatographic gels [5], catalysts [6,7] and batteries [8].…”

Nanoparticle diffusometry in hydrogels

“…The work already includes a critical discussion of the meaning of nanoparticle diffusometric data in polymer solutions using reptation and hydrodynamic concepts. model-free interpretation (Balakrishnan, Nicolai, & Durand, 2012;Croguennoc, Nicolai, Kuil, & Hollander, 2001) casein micelles and caseinate PFG NMR linear PEG (Mw = 1-600 kDa), dendrimers (Rh = 2-6 nm) obstruction effect, power law (Colsenet, Mariette, & Söderman, 2006a;Colsenet, Söderman, & Mariette, 2005b;2005a;Le Feunteun & Mariette, 2007;Le Feunteun, Ouethrani, & Mariette, 2012 , Langevin and Altenberger ) (Burke, Park, Srinivasarao, & Khan, 2000; Lattice Boltzmann simulations in model gel (Wassén et al, 2014) notes: (a) PEG = Polyethylene glycol, (b) PFG NMR = Pulsed-field gradient nuclear magnetic resonance, (c) CLSM = Confocal laser scanning microscopy, (d) FRAP = Fluorescence recovery after photobleaching, (e) FITC = Fluorescein isothiocyanate, a fluorescent dye, (f) DLS = Dynamic light scattering Table 2.4: Overview of applications of nanoparticle diffusometry in food related materials. The table includes systems studied, and instrumental methods and nanoparticles used.…”

“…Where the mobility of larger colloidal particles reflects the elastic properties of the gel (microrheology) , diffusion of smaller particles gives information about the details of gel sub-micron structure (nanoparticle diffusometry) (de Kort, van Duynhoven, Van As, Einhorn-Stoll & Drusch, 2015;. Nanoparticle diffusometry has been used in both polysaccharide Lopez-Sanchez, Schuster, Wang, Gidley, & Strom, 2015;Schuster et al, 2014a) and protein Salami, Rondeau-Mouro, Barhoum, van Duynhoven, & Mariette, 2014;Salami, Rondeau-Mouro, van Duynhoven, & Mariette, 2013;Schuster, Hermansson, Öhgren, Rudemo, & Lorén, 2014b) gels, or phase-separated mixtures thereof (Wassén et al, 2014). Both spherical particles and linear polymers such as dextran are sensitive to microstructural features in the gel.…”