Study On Rheological Characteristic Of Chestnut Protein Isolate And Preparation Of Its Peptides Technical

In this study chestnuts were used as the raw materials. The study was about theextraction methods of chestnut protein, which are reductant-alkali extraction-acidprecipitation and enzymatic extraction. Determining the optimal extraction conditionsof the two methods and comparing the extraction results of these two methods weredone in the beginning, Then rheology of protein extracted from chestnut was studied.And peptide of chestnut was prepared in the way of enzymatic hydrolysis. The resultsare as follows:1. In order to improve the extraction rate of the Chestnut protein, the method ofreductant-alkali extraction-acid precipitation to extract the chestnut protein was used.dissolution rate of soluble protein can be improved when use dithiothreitol andsodium sulfite as reductant in the extraction process of Chestnut protein. And theextraction rate of chestnut protein can be improved significantly. Optimal conditionsof chestnut protein extracted by the way of reductant-alkali extraction-acidprecipitation were drawn through single factor test and multi-factor orthogonal test.The optimal conditions were that the amount of0.50%Na₂SO₃,the amount of2.50%DTT, the concentration of0.05mol/L NaOH,1:11solid-liquid ratio and extractingprotein45mins in the temperature of35℃. Besides the extraction rate of chestnutprotein was85.36%. Compared with traditional alkali extraction of the chestnutprotein, the method of reductant compound alkali extraction and acid precipitationcould significantly improve the extraction rate of the chestnut protein. It could alsoprotect the chestnut starch, conducive to the comprehensive development andutilization of the chestnut, and reduce the concentration of alkali solution.At the sametime,it could reduce the pollution of the environment.2.The composite and alkaline protease were used and the ratio of the twoenzymes was determined, in order to improve utilization rate of raw material andextraction rate of protein. Make a secondary orthogonal rotation test after selecting the amount of enzyme, the pH of the extraction solution and solid-liquid ratio on thebasis of single-factor test. Then regression model for enzymatic extraction of proteinwas: Extractionrate=69.90+2.88A+2.81B+2.71C+0.77AB-0.39AC-1.56BC-5.59A²-6.40B²-1.94C².From the results of single-factor test and secondary orthogonal rotation test above, getthe best technology for the enzymatic extraction of chestnut protein: ratio ofcomposite and alkaline protease was1:2, enzyme dosage was4.25%, solid to liquidratio was1:30, temperature of extraction was36℃, pH value of extraction solutionwas8.6, time of extraction was3h. Under the conditions of extraction, the extractionrate of Chestnut protein was71.07%. Reductant-alkali extraction and acidprecipitation method had a higher extraction rate of chestnuts protein than enzymemethod.3.It couled be drawn from the rheometer that: the concentration of proteinsolution separated from Chestnut, the storage time, the temperature of the system, thecontinuous shearing time，the continuous shearing rate and other factors had animpact on fluid performance of protein solution isolated from Chestnut. The resultshowed that protein solution separated from Chestnut is a non-Newtonian fluid, andthe solution`s apparent viscosity decreased by the increase of shear rate and elevatedwith the increase of the concentration of the protein. In addition, when theconcentration of the protein solution increased, the phenomenon of shear thinning wasmore obvious. With the rise of the system temperature, the solution`s apparentviscosity was gradually reduced. the lower the concentration of protein solutionseparated from Chestnut, the lower activation energy and the resistance generatedwhen the solution flowed.4. The various factors,which affected the enzymatic process of chestnut peptideproduction,were systematically studied. The degree of hydrolysis （Y） and fourquadratic regression rotation combination model influenced by the factors wereestablished through orthogonal rotation combination trials.Y=23.78636-3.28038A-1.49844B+2.13604C+3.50501D-3.43029A²-1.28952D²,Papain was selected as enzymolysis tools of the chestnut protein. From the trialsstudies and computer simulations, the best parameter combinations of papain inChestnut protein enzymolysis was determined.They were suitable enzyme substratesratio of6%, Suitable substrate concentration of2.5%, the suitable pH of7.0, suitablereaction temperature of55℃and suitable reaction time of120min. And chestnutprotein degree of hydrolysis was31.15%.Under this best conditions of enzymolysisprocess, the best obtaining rate was35.11%in this experiment.