Rheological characterization of a pectin extracted from ponkan (Citrus reticulata blanco cv. ponkan) peel

The rheological properties of the optimized high-methoxyl pectin (PPOP), obtained from ponkan peel using nitric acid extraction (pH 1.6, 100 min, 36 ml/g liquid:solid ratio) were characterized. The flow behavior of aqueous and 0.1 M NaCl solutions at concentrations of 1%, 3% and 5% (w/w) was evaluated. The apparent viscosity of the solutions was directly related to the concentration. At the same concentrations and low shear rates the apparent viscosity values were close to those of a commercial citrus pectin. However, at higher shear rates, PPOP had a more shear thinning behavior. For both pectins, the presence of 0.1 M NaCl did not affect the apparent viscosity. The influence of pH, pectin and sucrose concentration on the gelling behavior of PPOP was investigated. Gelation occurred at pH < 3.5 and the strongest gel was obtained with 2.5% (w/w) pectin and 60% (w/w) sucrose at pH 2.5. The gel prepared under these conditions had viscoelastic behavior comparable to the gel prepared with a high-methoxyl commercial citrus pectin under the same conditions and displayed high thermal stability.