Setting temperature, pectin

The pectin solutions were mixed at 70°C with hot CaCl2 or CuCl2 solutions for 3 minutes and then poured into sealed tubes. After standing at least 48 hours at the setting temperature, the tubes were tilted and phase diagrams were determined by visual inspection. 

The gelation processes are not solely temperature dependent but also time dependent. The determination of the setting temperature is therefore dependent on the temperature profile being used. Results can only be compared, when the pectin preparations are pretreated and measured with exactly the same parameters. 

Hiemenz, P. C. (1986). Principles of Colloid and Surface Chemistry, 2nd ed. Dekker, New York. Hinton, C. L. (1950). The setting temperature of pectin jellies./. Sci. Food Agric. 1 300. 

FIGURE 9.9 Effect of pH on the relative strength (a) and setting temperature (b) of pectin gels (0.5%) in the presence of different sugars (68% w/w total solids). With permission from May and Stainsby (1986). 

The rate of dehydration of pectin has not been studied, but recently Hinton (12) and Harvey (7) have developed a theory of the setting temperature of pectin gels based upon the solubility of pectin in the gelling medium. The evidence favors the postulation that as the solubility of pectin decreases, the temperature of set increases or the time of set decreases. 

Pectin gels are a special case involving hydrogen bonding, and they require closely controlled conditions of sugar concentration and pH for their formation. The rate of set and the ultimate gel-strength vary with the temperature, but gelation itself is not temperature-dependent. 

Table I. Categories of High Methoxyl Pectin (Citrus) with Approximate Degree of Methylation, Setting Times, and Temperatures...

Dehydration of pectin requires time to come to equilibrium (to account for slow setting or low temperature of setting of certain pectin gels). 

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