Valencia PME isozymes create charge modified pectins with distinct calcium sensitivity and rheological properties

Pectin was de-esterified by U-PME or B-PME, pectinesterases that differed in cationic character and peptide composition. Pectin fractions of unmodified (O-Pec) and Valencia PME modified pectins (B-Pec and U-Pec) were separated by ion exchange (IEX) chromatography and characterized for calcium sensitivity by ζ-potential, texture profile analysis (TPA), and viscoelastic properties. U- and B-Pec had more negative ζ-potential than O-Pec, and became increasingly negative at higher pH values. Without CaCl_2, viscosity of O-Pec was higher than B- and U-Pec. With 35 mM CaCl₂, B- and U-Pec gelled, but O-Pec did not gel. TPA values were not significantly different between B-Pec and U-Pec. The G' values of O-Pec was 20-50-fold lower than G' for B-Pec or U-Pec. After separation with ion exchange chromatography, later eluting fractions formed stronger gels than earlier eluting fractions. However, pectin fractions had lower viscosity and G' values than unfractionated pectin, which is likely related to molecular weight differences. Results show that U-Pec forms stronger gels than B-Pec that is related to length of charge block and numbers of de-esterified pectin molecules.