Using Cyclic Voltammetry To Characterize The Change Of Casein Micelle’s Structure In The Milk Under Different Physicochemical Conditions

Milk is rich in protein.Casein micelles as an important part of protein whose structural stability have great influence on the stability of milk.Maintaining the stability of milk has been a core technology all the time.Therefore,the study of the casein micelles’ structure is the top priority of the milk quality research.This thesis aims to make a analysis to the casein micelles’ structure in milk and observe the changes of casein micelles in the processed milk through cyclic voltammetry.The thesis manages to improve the system of cyclic voltammetry,which lays a foundation for rapid determination of the adulteration and researching casein micelle structure of raw milk.First,detecting the raw milk that processed by heating,adjusting pH,and bringing exogenous calcium ions and EDTA into the raw milk through cyclic voltammetry to observe the changes.And isolating the casein micelle from the raw milk at the same time.Then,diluting it with the raw milk ultrafiltrate(10KDa ultrafiltration membrane)and detecting its electrochemical characterizations.The result shows that: With the increase of temperature,the current value in raw milk decreases,but the current value changes unsteadily when the temperature rises to 80 ℃;the oxidation peak current drops with the decrease of pH and the peak current value will increase when the pH is below 5.2,because most of protein in the milk is separated out;the increase of the concentration of calcium ions leads to the decrease of the peak current value;with the increase of the concentration of EDTA,the grain diameter of casein micelle will decrease.Secondly,The raw milk after being processed was stained with rhodamine B and the structure of casein micelle was observed by laser scanning confocal microscope.It was found that the aggregation of casein micelle was obvious after heat treatment.Once the pH was reduced to 5.8,the particle size of casein micelle increased,and when the pH was reduced to 5.2,some proteins precipitated out,while when the pH was reduced to 5.0,the protein precipitated out basically,and the colloidal structure was destroyed.Finally,the particle size of casein micelles in raw milk was determined by particle size analyzer.The results showed that the particle size of casein micelle did not change significantly after different heating intensities;And the particle size of casein micelles increased with the decrease of pH;And after introducing exogenous calcium ions,the particle size of casein micelles increased with the increase of calcium ion concentration;And the particle size of casein micelle decreased with the increase of EDTA concentration.In addition,a cyclic voltammetry detection system was established to detect the different hot processing of raw milk by comparing the oxidation peak current value of raw milk and processed milk,so as to determine the process of hot processing raw milk.To sum up,after heating,adjusting pH,introducing exogenous calcium ions,and adding EDTA,the structure and particle size of casein micelle in raw milk changed significantly,which caused the change of oxidation peak current value in raw milk.The change of casein micelle structure was detected by the change of oxidation peak current in raw milk.