Gelation of high methoxy pectin in the presence of pectin methylesterases and calcium

High methoxy pectin was submitted to various amounts of a fungal pectin methylesterase (PME) from Aspergillus aculeatus and of a plant PME from orange in the presence of calcium. The systems were characterized by rheological means during the gelation process. By the way of in situ demethoxylation with low amount of orange PME, it was possible to gel pectin from the beginning of the reaction although its high degree of methylation around 70. To understand this unusual properties, the behaviour of the two enzymes was investigated in pectic gels and in solution through the analysis of content and distribution of the remaining methyl esters. In the gel, the degree of methylation decreased slowly with orange PME and rapidly with Aspergillus PME. The degree of methylation and degree of blockiness after treatment with each PME in solution or in gels were slightly different. Possible explanations for this are evolving visco-elastic properties, including gel formation or influence of calcium on the enzyme–substrate complex.