Pectic acid

The degree of methylation is devided in five destinct categories [2]:
1) 30 DM for low sugar gels.
2) 45 DM pectin for rapid-setting calcium-precipitable pectin suitable for high-sugar gels and emulsions.
3) 60 DM or slow-set pectin for high sugar gels and confectionary jellies.
4) 74 DM for typical rapid-set pectin for jams and jellies.
5) higher DMs for special-purpose applications.

Sometimes the following destinction is used [2]:
1) Rapid-set, 70% DE or higher.
2) Slow-set, 50-70% DE.
3) Low methoxy pectin 50% DE or lower.

The solubility decreases with the increase of lenght and the decrease of methoxyl groups [2].

The viscousity of pectin solutions depends on DM, concentration, pH, presence of salts and their concentration and temperature. No gel is formed above pH 3.6. Optimum performance for slow-setting pectins is mostly 2.8-3.2 and for rapid-setting pectins it is mostly pH 3.0-3.4. The effect of pH, however, is not entirely predictable. The effect of alkali metal ions is not predictable either. At low pH the presence of alkali metal ions will increase the viscousity, but at pH ~6 the viscousity is solely dependent on the lenght and shape of the chains. Calcium can increase viscousity of pectin even at pH 8.55. The viscousity increases at lowering the degree of methylation as calcium cross-link the pectin chains [2]. Experiments with calcium also suggests that gelling is initialized by binding of Ca²⁺, followed by network formation through chain/chain association [7].

The gelling of pectin is removed if the pectin is converted into the ethyl- og 2-hydroxyethyl ester [6]. This show that there is a steric fit between methyl D-galactopyranosiduronate residues in the helix-forming junctions [6]. One actylation per eight residues is enough to diminish the gelling drastically [6].

An experiment on swelling of pectin gels as a function of the concentration of Ca²⁺ show, that the neutral components of the network does not have a high affininty for water [7].

The affinity for divalent ions like Ca²⁺ increases with decreasing DE and increasing length of galacturonan backbone. High DE pectins have been observed to gel in the presence of Ca²⁺, this is believed to be the an "eggbox" conformation in which Ca²⁺-ions are enclosed [7].