title: External and internal gelation of pectin solutions: microscopic dynamics versus macroscopic rheology.
abstract: Pectin is a natural biopolymer that forms, in the presence of divalent cations, ionic-bound gels typifying a large class of biological gels stabilized by non-covalent cross-links. We investigate and compare the kinetics of formation and aging of pectin gels obtained either through external gelation via perfusion of free Ca(2+) ions, or by internal gelation due to the supply of the same ions from the dissolution of CaCO3 nanoparticles. The microscopic dynamics obtained with photon correlation imaging, a novel optical technique that allows obtaining the microscopic dynamics of the sample while retaining the spatial resolution of imaging techniques, is contrasted with macroscopic rheological measurements at constant strain. Pectin gelation is found to display peculiar two-stage kinetics, highlighted by non-monotonic growth in time of both microscopic correlations and gel mechanical strength. These results are compared to those found for alginate, another biopolymer extensively used in food formulation.
authors.affiliation: Dipartimento di Chimica, Materiali e Ingegneria Chimica, Politecnico di Milano, 20133 Milano, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Secchi
authors.forename: F
authors.initials: F
authors.lastname: Munarin
authors.forename: M D
authors.initials: MD
authors.lastname: Alaimo
authors.forename: S
authors.initials: S
authors.lastname: Bosisio
authors.forename: S
authors.initials: S
authors.lastname: Buzzaccaro
authors.forename: G
authors.initials: G
authors.lastname: Ciccarella
authors.forename: V
authors.initials: V
authors.lastname: Vergaro
authors.forename: P
authors.initials: P
authors.lastname: Petrini
authors.forename: R
authors.initials: R
authors.lastname: Piazza
mesh_terms: D000464:Alginates / Q000737:chemistry*; D002118:Calcium / Q000737:chemistry*; D003198:Computer Simulation; D005782:Gels; D020723:Glucuronic Acid / Q000737:chemistry; D006603:Hexuronic Acids / Q000737:chemistry; D007700:Kinetics; D008854:Microscopy, Electron; D015394:Molecular Structure; D010368:Pectins / Q000737:chemistry*; D012212:Rheology; D013816:Thermodynamics
chemical_list: D000464:Alginates; D005782:Gels; D006603:Hexuronic Acids; D010368:Pectins; D020723:Glucuronic Acid; D002118:Calcium