Study On Extraction And Purification Technology Of Pectin From Sweet Potato Residue And Its Physicochemical Properties

In this thesis, extraction, separation, purification, structure and physicochemical properties of pectin from sweet potato residue were investigated. And the pectins extracted by different methods were compared with each other. These works would have academic significance for taking full advantage of the sweet potato resources to enhance the development of processing industry and solved the residue contamination problems.The main contents and results were as follows:1. The parameters for removing starches in Sweet potato residue. The optimum conditions of high-temperaturea-amylase were:Solid-liquid ratio1:15, temperature90℃, pH6.0, time30min. The best conditions of medium-temperature a-amylase were:temperature70℃, pH6.0, time30min. The optimal conditions of glucoamylase were:temperature60℃, pH4.5, time90min. The reaction rate is fast with high-temperaturea-amylase in these conditions,therefore, which can be used to remove starch of sweet potato residue.2. Extraction of sweet potato pectin. Sweet potato pectin was extracted with hydrochloric acid, sulfurous acid, ammonium oxalate, potassium oxalate, sodium polyphosphate solution. The results showed that the extracting efficiency of ammonium oxalate was the best. Single factor experiments were used to determine the level of the factors and response surface experiments were designed to optimize the parameters, the results showed that the best conditions were:concentration of ammonium oxalate5mg/mL, temperature95.07℃, time1.93h, pH5.8, solid-liquid ratio1:50. under these conditions the extraction rate of pectin and purity were11.29%and72.95, respectively.3.Purification of sweet potato pectin.sweet potato pectin was decolorizated with activated carbon, diatomaceous earth, ultrafiltration and ion exchange resin. The protein was hydrolyzed protease. The results showed that the better decolorization conditions were: activated carbon dosage:2.0%, temperature50℃, time40min. The reflux rate was87%to92%with ultrafiltration membrane decolorization. The process was simple and low cost. The other small molecules were also removed during this process. It was also suitable for industrial continuous production.4.Physico-chemical properties analysis of sweet potato pectin. The sweet patato pectin obtained by acid extraction methods and salt extraction methods was analysed and compared with the apple pectin in the aspects of esterification degree, gel strength, viscosity and purity. The results showed that the properties of pectin by salt extraction were as follows: purity81.5±4.3%, viscosity22±4.6%, degree of esterification58.2±3.5%, gelation146.1±3.5%. Combined with the data of NMR and IR, this substance was a conformation. The sweet potato pectin by Salt extraction was with high purity, better water solubility and physicochemical characteristics than that by acid extraction and suitable for application in the food industry...