Effects of calcium, pH, and blockiness on kinetic rheological behavior and microstructure of HM pectin gels.
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.
Löfgren
Caroline
C
SIK, The Swedish Institute for Food and Biotechnology, P.O. Box 5401 SE-402 29 Göteborg, Sweden.
Guillotin
Stéphanie
S
Evenbratt
Hanne
H
Schols
Henk
H
Hermansson
Anne-Marie
AM
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
D005782:Gels; D013395:Sucrose; D010368:Pectins; D002118:Calcium