Stiffness of Ca2+-pectin gels: combined effects of degree and pattern of methylesterification for various Ca2+ concentrations Original Research Article

The influence of the degree and pattern of methylesterification (DM and PM, respectively) on the stiffness of Ca2+-pectin gels is extensively examined, at various Ca2+ concentrations. Accordingly, a highly methyl-esterified pectin was selectively de-esterified using NaOH, plant or fungal pectin methylesterase in order to produce series of pectins with varied pattern and broad ranges of methylesterification. The PM was quantified as absolute degree of blockiness (DBabs). Ca2+-pectin gels were prepared at various Ca2+ concentrations. Gel stiffness (G′ at 1 rad/s) was determined and mapped out as a function of DM, DBabs and Ca2+ concentration. At low Ca2+ concentrations, G′ depends on polymer’s DM and DBabs. At high Ca2+ concentrations, a master curve is obtained over a wide range of DM, irrespective of DBabs. Depending on methylesterification pattern, increase of G′ is related not only to an increase in the number of junction zones per pectin chain, but also to an increase in the size of junction zones and the number of dimerised chains occurring in the gels. These results provide a detailed insight into the occurrence of junction zones in Ca2+-pectin gels.