Characterization of the pectin extracted from citrus peel in the presence of citric acid

Pectins were extracted from the peel of Citrus unshiu Marcovitch × C. nobilis Loureiro (Kara mandarin) in the presence of citric acid at different pH and temperature. Treatment with citric acid, particularly, at neutral pH gave a significant increase in viscosity. The citric acid treatment at high temperature led to decreased viscosity although the viscosity remained higher than that of untreated pectin. Pectin methylesterase activity was inhibited at high citric acid concentrations. The increase in viscosity of treated pectin was proportional to the amounts of citric acid bound to pectin. The pectin with citric acid treatment had a low degree of methylation (8.4%) and a high distribution (50 to 2000 kDa) of molecular mass than untreated pectin. Analysis of chemical composition showed that the pectin with citric acid treatment contained lower protein and galacturonic acid, and higher neutral sugars, particularly, galactose than the untreated pectin. The citric acid treatment at neutral pH prior to extraction is an attractive procedure for low methoxy pectin without lowering its molecular weight.