Degradation Analysis Of Pectin Treated By Microwave And High-speed Shearing

Pectin is an acid hetropolysaccharides extracted from plant cell wall. As anatural food additive and drug auxiliary materials, pectin has been widely used infood, medicine and cosmetic industry. In the food industry, pectin is commonly usedas gelling agent, thickener, texturizer, emulsifier and stabilizer to modify properties offood systems. HSS was used in this study to eliminate the aggregation of pectins. Theeffect of HSS on disaggregation and degradation of pectin from creeping fig seedswas systematically studied. The pectin treated by microwave extraction catalytictesting machine was used to study the degradation of pectin, discusses the changes ofstructural properties of pectin, and test the degradation kinetics, rheological propertiesand the gel of pectin. The main conclusions are as follows:1. It was found disaggregation and degradation occurred during the wholeshearing process. When pectin solution was sheared at24,000rpm for less than8h,degradation happened but disaggregation was dominant during this period. After8h,degradation became obviously, however, a small amount of aggregates remained evenafter24h treatment, indicating that HSS may not eliminate aggregates efficiently. Anew method was proposed for calculating more accurate molecular weight based onthe change of reducing sugars content and variation of molecular weight.Determination of unsaturated uronide and FT-IR spectra analysis indicated neitherβ-elimination nor demethoxylation occurred during the HSS, and no new functionalgroup was formed during the HSS process.2. Based on the change of reducing sugars and unsaturated substances of pectin,the acid hydrolysis was dominated under acidic conditions, and the mechanism ofpectin degradation was β-elimination under alkaline conditions. It was found thatdemethylation was happened by the determination of titration and infrared spectraunder alkaline conditions. With the processing time increased, the particle size ofpectin was reduced under acidic conditions; while the particle size of pectin was reduced at first, then it was increased under alkaline conditions. The breakdown ofglycosidic bonds was not only owing to the thermal effects of microwave but alsofrom non-thermal effects i.e. the effects of free radicals.3. At pH9.0and pH3.83, microwave power210mA, the microwave degradationof pectin followed the first-order kinetics. At pH1.5, the microwave degradation ofpectin deviated from the first-order kinetics. With the microwave time increasing,pectin gel gradually weakened and all the pectin gel are presented in the solid state atpH3.83.With the frequency of increasing, all pectin gels are presented shear thinningphenomenon. At pH1.5and pH9.0, pectin gels obviously depended on the changes ofthe frequency, the formation of gel like liquid state. By the analysis of pectin geltexture, it was found that gel strength, gel elasticity, hardness, stickiness, chewinesswere reduced with increasing microwave time. When the time was30min, theviscosity of the pectin gel was negative, indicating pectin gel was in the fluid stateafter30min.