Effects Of Different Processing Methods On Allergenic And Functional Properties Of Alpha-Casein In Bovine Milk

Milk is one of the most popular foods because it contains high amount of various nutrients and bioactive components.However,milk is also one of the most common food causing strong allergic reactions.Therefore,it is important to research the processing methods to reduce milk allergenicity,ensure food safety and retain nutrients.In this study,the effects of high hydrostatic pressure(HHP),ultraviolet light-C(UV-C),and far-infrared(FIR)treatments on the morphology,structural properties,allergenicity,digestibility and other bioactivities of α-casein from bovine milk were studied.The physicochemical properties and microbiological characteristics of the raw milk were also analyzedHigh-pressure process at the pressure levels of 200 and 600 MPa with different cycles and times,ultraviolet light-C and far-infrared processing with different times were implemented on α-casein.The atomic force microscopy,fourier transform infrared spectrum,sulfhydryl content,surface hydrophobicity and 1H NMR analysis were utilized to investigate the changes of morphology and structure of α-casein after different treatments In addition,the change of the allergenicity of α-casein was evaluated.The roughness of α-casein was increased and the β-sheet content was decreased significantly with the change in sulfhydryl content and surface hydrophobicity,especially after 600 MPa HPP treatment.Intrinsic tryptophan fluorescence absorbance of α-casein was decreased significantly after 15 min UV-C treatment.While HPP reduced the allergenicity of α-casein,15 min UV-C showed more significant decrease in allergenicity These results indicated that protein structures and the allergenicity of α-casein were changed after HHP and UV-C treatments which may caused by protein unfolding and exposure of hydrophobic groupThe changes in protein oxidation,digestibility,antioxidant and antihypertensive activities of a-casein after HHP,UV-C and FIR treatments were investigated,and the functional peptides after α-casein hydrolysis was also analyzed by ultra-performance liquid chromatography-tandem mass spectrometry.UV-C caused maximum protein oxidation,especially for 15 min treatment.ACE-inhibitory activity and antioxidant activity were increased in different levels,in which 5 min of 200 MPa HPP treatment significantly increased the peptides that have the antihypertensive activity However,the peptides related with allergenicity and antioxidant activity were decreased after 15 min UV-C treatmentSoluble solids content,pH,conductivity,color and microbiological characteristics of raw milk were analyzed.The results showed no significant differences in soluble solids content,but pH and conductivity were increased after different treatments.The 15 min UV-C treatment changed the milk color in maximum degree.Aerobic plate count and coliform count were decreased,below the limit of GB19645-2005 standard after different processing methods.Therefore,HHP,UV-C and FIR are effective in preserving quality and controlling the microbiological characteristics of raw milk.This study suggested that HHP,UV-C and FIR treatments are potential for dairy product processing.