Decolorization Of Beet Pulp Pectin By Macroporous Resins And Properties Of Some Different Molecular Weight Decolorized Pectin

In this paper, the optimal decoloring process conditions of beet pulp pectin usingmacroporous resin treatment were investigated. The effects of decoloring processes onstructure and properties of pectin located both in suspension layer and precipitation layer werecompared. The beet pulp pectin with different molecular weight was fractionated byultrafiltration. The conditions and feasibility of classification of beet pulp pectin byultrafiltration were evaluated. The structure characterization, the rheological property,emulsification property and antioxidant capacities of beet pulp pectin with different molecularweight were determined and compared.The main research contents and conclusions were as follows:1. The decolorization process of beet pulp pectinBased on the decoloring rate and recovery as indexes, the optimal decolorization conditions ofbeet pulp pectin using D101resin were investigated. The results showed that the optimalconditions for static decolorization were pH1.8, the ratio of resin/liquid2g:25mL,temperature90℃and time60min. Under the optimal conditions, the decoloring rate andrecovery of beet pulp pectin were74.36%and75.76%, respectively; When the optimalconditions for dynamic decolorization were velocity2BV/h, the Brix2.5Bx and thetreatment capacity up to10BV, the decoloring rate still reached80.99%. Desorptionconditions were ethanol70%, velocity2BV/h and temperature25℃. When the desorptionwas repeated four times and the treatment capacity was10BV, the decoloring reached68.08%.2. Changes in the properties of beet pulp pectin by resin decolorationThe effects of decoloring processes on properties of native pectin, pectin located both insuspension layer and precipitation layer were compared. The results showed that the degree ofesterification, galacturonic acid content and molecular weight increased, while the ferulic acidand neutral sugar content dropped. However, the structure of pectin didn’t change. Theproperties of beet pulp pectin in suspension layer were better than that in precipitation. Afterdecoloring, the colour of pectin was shallower and the quality of pectin was better.3. The Structure and Properties of Beet pulp Pectin Fractionated by UltrafiltrationThe optimal conditions of ultrafiltration were the concentration of pectin solution1g/L,operating pressure0.025MPa, liquid temperature40℃. Under this conditions, the actualmolecular weights of four fractions were close to the theoretical values. The purity was muchhigher. This result indicated that ultrafiltraction used for beet pulp pectin fractionation was good. The content of pectin with above100000Da of molecular weight accounted for64.86%,while the content of pectin below20000Da was only3.89%. The structure and properties ofpectin with different molecular weight were analysed. The results showed that thegalacturonic acid content, ferulic acid content and degree of esterification gradually decreasedwith the decrease of the molecular weight. The kinds of monosaccharide decreased with thedecrease of molecular weight, while the total content of monosaccharide increased with thedecrease of molecular weight.4. Rheological and emulsification properties of beet pectin with different molecular weightsThe rheological and emulsification properties of beet pectin with different molecular weightwere investigated. The results showed that with the increase of molecular weight,concentration of pectin, salt concentration and the added amount of sucrose, the apparentviscosity of beet pulp pectin increased. With the shear rate and temperature increasing, theapparent viscosity of pectin solution dropped. With the changes of pH, the viscosity of pectinfirst increased and then dropped. When the pH was3.5, the apparent viscosity reached up tothe largest point. The solutions showed the typical shear-thinning non-Newtonian fluid. Thepectin with4.64×104Da had the best emulsifying activity.5. The antioxidant properties of beet pulp pectin with different molecular weightsThe DPPH results showed that the pectin with a theoretical molecular weight>100000Da hadthe strongest antioxidant capacity; The ORAC results showed that the pectin with thetheoretical molecular weight of50000-100000Da had the strongest antioxidant capacity. Thedifferent results may be attributed to the differences of free radicals, characteristics ofreactants and antioxidant mechanism in those two kinds of methods.