New Principles And New Methods Of Total Protein Content Of Foods Moving Reaction Boundary Titration

There is a long history about the determination of food protein content andvarious kinds of methods have been used, but many problems have been found suchas complicated operating procedures, long time and the weak resistibility to NPN(non-protein nitrogen). In this thesis, Moving Reaction Boundary Titration thatbased on Moving Reaction Boundary has been proposed, and been used todetermine the total protein content of infant formula milk powder and soya-beanmilk. The experimental results demonstrate that this method can determine the totalprotein milk with high precision in few minutes and it can resist the interference ofNPN effectively.Concrete research content including following several aspects:1. Theory of protein content titration using Moving Reaction Boundary TitrationIn the Chapter2, the method using NaOH to titrate protein content in liquidsamples based on the concept of Moving Reaction Boundary is proposed. The OH-incatholyte can react with the acid residues on protein. The experiments reveal that (1)the proteins in samples have been immobilized in polyacrylamide gel completely;(2)H+can also been used to titrate the protein content in liquid samples via reactingwith the amino groups on protein;(3) only protein can react with OH-, othermaterials in samples won’t interfere the reaction;(4) the voltage, the content ofbackground electrolyte (KCl) and the concentration of NaOH have evident influenceon the boundary movement, therefore they also have influence to the determinationof protein content.2. The determination of protein content in infant formula milk powderIn the Chapter3, on the basis of the method proposed in Chapter2, we selectfive kinds of infant formula milk powder and determine their protein content, furtherprove the feasibility of this Moving Reaction Boundary Titration method. Theexperiments reveal that (1) the linear relation between the distance (D) MRB movesand the run time (t) demonstrates the uniform velocity of MRB;(2) there is a goodlinear relation between velocity of MRB (VMRB) and total protein content in sample, so we can obtain the protein content via recording the velocity of MRB;(3) NPN suchas melamine and urea won’t interfere the determination of protein content;(4) theresults from MRBT agree with kjeldah method very well, certifying the goodsensitivity of MRBT method;(5) the experiment is repeated three times a day and therelative standard deviation is between1.16%to7.41%, demonstrating goodrepeatability of this method.3. The determination of protein content in soya-bean milkIn the Chapter4, we determine the protein content of four kinds ofsoya-bean milk under the optimum conditions obtained in Chapter2. Theexperiments reveal that (1) when the protein content is fixed, there is a good linearrelation between the distance that MRB moves and run time, demonstrating that theMRB moves at a constant rate;(2) the velocity of MRB is a function of proteincontent, we can obtain the protein content via recording the velocity of MRB;(3)NPN such as melamine and urea won’t interfere the determination of proteincontent;(4) the sensitivity of MRBT method correspond to kjeldahl method;(5) theexperiment is repeated three times a day and the relative standard deviation isbetween0.57%to4.39%, demonstrating good repeatability of this method.The proposed method can be used for large-scale samples determination. First,the protein content of one sample can be determined in kjeldahl method as astandard, and then make the standard curve using MRBT method. At last, we canobtain the protein content of the large-scale samples from the standard curve.