title: Effects of calcium, pH, and blockiness on kinetic rheological behavior and microstructure of HM pectin gels.
abstract: The kinetic behavior during gel formation and the microstructure of 0.75% high methoxyl (HM) pectin gels in 60% sucrose have been investigated by oscillatory measurements and transmission electron microscopy for three comparable citrus pectin samples differing in their degree of blockiness (DB). Ca2+ addition at pH 3.0 resulted in faster gel formation and a lower storage modulus after 3 h for gels of the blockwise pectin A. For gels of the randomly esterified pectin B, the Ca2+ addition resulted in faster gel formation and a higher storage modulus at pH 3.0. At pH 3.5, both pectins A and B were reinforced by the addition of Ca2+. In the absence of Ca2+, the shortest gelation time was obtained for the sample with the highest DB. Microstructural characterization of the gel network, 4 and 20 h after gel preparation, showed no visible changes on a nanometer scale. The microstructure of pectins A and B without Ca2+ was similar, whereas the presence of Ca2+ in pectin A resulted in an inhomogeneous structure.
authors.affiliation: SIK, The Swedish Institute for Food and Biotechnology, P.O. Box 5401 SE-402 29 Göteborg, Sweden.
authors.forename: Caroline
authors.initials: C
authors.lastname: Löfgren
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Guillotin
authors.forename: Hanne
authors.initials: H
authors.lastname: Evenbratt
authors.forename: Henk
authors.initials: H
authors.lastname: Schols
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Hermansson
mesh_terms: D002118:Calcium; D005782:Gels / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D046529:Microscopy, Electron, Transmission; D015394:Molecular Structure; D010368:Pectins / Q000737:chemistry*; D012212:Rheology; D013395:Sucrose
chemical_list: D005782:Gels; D013395:Sucrose; D010368:Pectins; D002118:Calcium