Research On Protein Recovery From Potato Juice And Protein Properties

China is the largest producer of potato and the annual output of potato isabout70million tons. Most potatoes are used to produce starch at industrialscale. Annually,400thousand tons starch are produced and2million tonspotato juice (PJ) are generated. Protein is the major organics in potato juice.Potato protein is a kind of high-quality plant protein and has great potentialvalue, but it is discharged directly, which pollutes environment and is wastefuluse of resource. Therefore, the methods of potato protein recovery from potatojuice were studied and the protein functional properties were determined. Theresults are as follows:(1) Composition determination of industrial potato juice. The resultsshowed that potato juice contained97.16%moisture,0.47%starch and1.23%protein.(2) Potato juice preparation in laboratory. To obtain starch and potato juice,the processing steps included cutting, color protecting, crushing, dregsremoving, centrifuging and drying. The results showed that the protein contentof laboratory potato juice was similar to that of industrial potato juice.(3) Potato protein recovered by isoelectric point method. The processconsisted of adjusting pH, controlling temperature, centrifuging, neutralizingand drying. The process was optimized by orthogonal experiment. The optimumconditions were: pH4.5±0.2, temperature60±2℃, processing time40min.Recovery rate of protein was51.19%, protein purity was84.49%.(4) Potato protein recovered by flocculation. Carboxymethyl cellulose(CMC), chitosan, sodium alginate and polyacrylamide were used as flocculants.The process consisted of adding flocculant, adjusting pH, controllingtemperature, centrifuging, neutralizing and drying. The process was optimizedby orthogonal experiment.①Optimum conditions of CMC flocculation were:addition of CMC30mg/100mLPJ, pH4.0±0.2, temperature30±2℃, processingtime40min. Recovery rate of protein was69.72%, protein purity was77.53%. ②Optimum conditions of chitosan flocculation were: chitosan amount7mg/100mLPJ, pH4.5±0.2, temperature70±2℃, processing time40min.Protein recovery rate was73.90%, protein purity was78.55%.③Optimumprocess of sodium alginate flocculation were: amount of sodium alginate20mg/100mLPJ, pH4.0±0.2, temperature50±2℃, processing time40min.Recovery rate of protein was65.72%, protein purity was76.62%.④Optimumprocess of polyacrylamide flocculation were: polyacrylamide amount6mg/100mLPJ, pH4.0±0.2, temperature60±2℃, processing time30min.Protein recovery rate was57.55%, protein purity was72.33%.(5) Potato protein recovered by ultrafiltration. The process consisted ofadjusting pH, controlling temperature, ultrafiltering and drying. The process wasoptimized by orthogonal experiment. The optimal process conditions were:operating pressure0.10±0.01Mpa, temperature25±2℃, pH4.5±0.2. Recoveryrate of potato protein was78.96%, protein purity was82.67%.(6) Determination of potato protein molecular weight. The samples wereanalyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis(SDS-PAGE). The results showed that: potato protein recovered by isoelectricpoint appeared only one band, the molecular weight was49.0kD; potato proteinflocculated by CMC and chitosan showed three bands, the molecular weightswere:49.0kD,25.7kD,22.4kD, respectively. Therefore, only one kind of potatoprotein was recovered from isoelectric point method, kinds of potato proteinwas recovered from CMC and chitosan flocculation.(7) Protein samples dried at50℃were browning.Freeze-drying protein islight in color, but the cost is high. Therefore, drying method of potato proteinwill need to be further investigated.(8) Determination of potato protein functional properties. Functionalproperties of potato protein flocculated by CMC were determined, such as:solubility, water holding capacity, foaming and foam stability, emulsifyingproperties and emulsion stability, viscosity, and compared these properties ofsoy protein isolate. The results showed that the functional properties of potatoprotein and soy protein isolate were similarly affected by pH, temperature,protein concentration, NaCl, and other factors, but the functional properties ofsoy protein isolate were better than those of potato protein obttain in this project.