Rheological properties of deesterified pectin with different methoxylation degree

High methoxylated citrus pectin was deesterified by alkaline or pectin methylesterase (PME) to produce pectin with various methoxylation degree (DM) from ~50% to < 10%. Alkaline deesterification (p < 0.05) was effectively achieved at pH> 10. At pH 12 pectin DM could be reduced to lower limit of 15.91 ± 2.55% under 4 ℃ after 300 min but further to 6.81 ± 1.46% under 20 ℃ within 30 min. Stronger alkaline treatment led to heavier pectin degradation, especially suggested by the statistically significant (p < 0.05) reduction of weight-average molecular weight (Mw). Namely the heavy pectin chains were disrupted by alkaline. Enzymatic deesterification using ROHAPECT MPE resulted in a DM of 28.78 ± 0.78% with 0.1% (w/w) enzyme amount and further to 14.67 ± 0.80% with 1.5% (w/w) enzyme amount within 5 h. Correspondingly, the enzymatic-deesterified pectin (DM=14.67 ± 0.80%) presented a much higher intrinsic viscosity ([η]) of ~2000 mL/mg in comparison to raw material (~1600 mL/mg) while the alkaline-treated pectin (DM=10.81 ± 1.85%) had a low [η] of ~700 mL/mg due to chain decomposition. Microscopic gelling of all the alkaline deesterified pectins was Ca2+-dependent (> 44 mg/g), but particularly the product with DM of 9.36% could gel at low Ca2+ concentration (4-8 mg/g). Enzymatic deesterified pectin produced by RAPIDASE® PEP (DM 30.83%) and ROHAPECT MPE (DM 14.67%) could gel at pH 2 in the absence of Ca2+ and their Ca2+-dependence increased with pH increase, while the product by NOVOSHAPE KEN00536 always needed > 24 mg/g Ca2+ for gelling under pH 2.0-4.0.