Composition Analysis Of Milk Protein Denaturation Aggregation In Different Heating Degree Skim Milk Powders

Skim milk powder is important food material,during skim milk powder production process heat-induced whey protein denaturation occurs.According to the content of undenatured whey protein,the skim milk powder can be classified as low,middle,high heated skim milk powder.Different heating degree skim milk powders has different funtional properties and processing properties,can be used in different products.In order to understand the mechanism of whey protein denaturation,we started from the different heating degree skim milk powders and analysed their functional properties.The different heating degree skim milk,intermediate products of making skim milk powders,were used as controls.The analysis of aggregation was from two directions,the products and the semiproducts.Then we used the component simulated experiment to verify the mechanism of aggregation producing process.The foaming capacity and foaming stability of skim milk powders decreased with increasing heating temperature;the emulsifying property and emulsifying stability of skim milk powder also decreased with increasing heat degree;the skim milk powder's dispersity decreased with increasing the temperature,but the wettability increased with increasing heating temperature.The scanning electron micrograph of samples showed that the casein micelles and whey protein would form aggregation after heat treatment.The aggregation would grow larger as the heating degree increased.The fourier transform infrared spectrometer was used to determine the secondary structure of milk protein.The result showed that the content of random coil increased as the treating temperature increased,indicating that the heat treatment leading to the secondary structure of protein changing.The two-dimentional electrophoresis method was used to analyse the composition of aggregation.The gel pores and boundaries of separation gel and stacking gel of the first-dimentional gel were used as samples of the second-dimentional electrophoresis after treatment with 2-mercaptoethanol.The results showed that the amount of aggregation in gel pore was increased as the heating temperature increased,but the aggregation amount in boundaries of separation gel and stacking gel was decreased.The aggregation was mainly formed by disulfide bond.The aggregation in gel pore was mainly formed by whey protein and ?-CN,while the aggregation in boundaries of separation gel and stacking gel was mainly formed by ?s2-CN and ?-CN.The component simulated experiment found that ?-Lg contains a free sulfydryl group,is the main whey protein that took part in denaturation.Single a-La solution was lack of free thiol,it was difficult for a-La to form aggregation.Adding ?-Lg to a-La would bring in free thiol,that would promote a-La's aggregation.The denaturation mechanism of BSA was similar to ?-Lg,cause BSA has a free sulfydryl group too.The BSA aggregation was also formed by disulfide bonds,but it tend to form aggregation by themselves.The ?-CN lost the activity when isolated from milk because they would form polymer at once.