Study On Structural And Functional Properties Of Casein And Whey Protein By High-pressure Homogenization And Ultrasonic Treatment

Both high-pressure homogenization and ultrasound are new types of non-thermal food processing technologies,and both process liquid and semi-solid foods with their own processing technology characteristics.There are still many problems to be solved if these two technologies are to be widely used in food processing,such as impact on the structure and functionality of food components and food safety evaluation.In this study,two non-thermal processing technologies,high-pressure homogenization and ultrasound,were used to treat casein and whey protein.The influences of the two technologies on the structure,functional properties,allergenicity and in vitro simulated digestibility of two cow's milk proteins were preliminarily discussed.Various spectroscopic techniques such as fluorescence spectroscopy,ultraviolet-visible absorption spectroscopy,and circular dichroism were used to analyze the changes in the molecular structure of two proteins.In addition,the functional characteristics such as solubility,foaming and emulsifying properties were compared.Finally,the effects of processing on allergenicity and in vitro simulated digestibility were compared.The research provides a certain experimental and theoretical basis for the rational selection of new non-thermal processing techniques,especially high-pressure homogenization and ultrasound.The main research contents and results of this article are as follows:1.The working principles of high-pressure homogenization and ultrasonic technology,as well as the research progress of non-thermal technology were briefly described;The structure,function and distribution of two main complex proteins in milk,casein and whey protein,were introduced.The research methods of protein conformation,functional characteristics and allergenicity were briefly described.2.The conformation and surface hydrophobicity of casein and whey protein were studied by using fluorescence spectroscopy,ultraviolet-visible absorption spectroscopy,circular dichroism and hydrophobic fluorescent probe methods.The results showed that the secondary and tertiary structure of casein and whey protein changed as the highpressure homogenization pressure increased,hydrophilic amino acid residues were more exposed,hydrophilic regions increased,and surface hydrophobicity became worse.While the ultrasonic processing is softer than the high-pressure homogenization processing,the anti-parallel structure of the protein after treatment was increased,the stability was relatively improved.Furthermore,more non-polar groups,hydrophobic side chains appeared so that the hydrophobic effect increased.3.Changes in protein solubility,foaming,emulsifying,allergenicity and in vitro simulated digestibility were studied.The results showed that under high-pressure homogenization conditions,casein was more soluble in water,and the precipitation was significantly reduced after centrifugation.Besides,the foaming properties of the two proteins showed a trend of falling first and then rising.The foaming stability was steadily enhanced,and the emulsification properties in the oil/water system were also improved.However,the emulsification stability exhibited a fluctuation characteristic with the increase of pressure or power.It was worth noting that the allergenicity of both proteins was effectively reduced,in addition to this,the digestibility was also improved.After ultrasonic treatment,the solubility of the two increased slightly,the foaming properties and the ability to form emulsion were enhanced,the digestibility was increased,on the contrary,the emulsion structure could not be maintained well.The binding capacity of the two proteins to Ig E was significantly different.