Preparation And Functional Properties Of Whey Protein Microgel

Whey protein is rich in essential amino acids,has high biological value and various functional properties,and has a wide range of applications in food processing.Microgel is a kind of soft,deformable particles,in which biomolecules are able to retain solvent molecules to form microgel through hydrophobic bonds,hydrogen bonds and electrostatic interactions.Whey protein microgel has excellent functional properties,such as stabilizing Pickering emulsions and forming stable foams.However,microgels are applied only at locations far from the isoelectric point of whey protein,and the ultrasonic treatment can be used to influence the structure of microgels and improve their functional properties.Therefore,ultrasonic treatment was performed during the preparation of microgels to try to change their surface polarity,charge,and stability to influence their functional properties.This study focused on the effects of preparation methods on the structure and physicochemical properties of whey protein microgel,and examined the effects of preparation methods on its gelation and emulsification properties.The main conclusions obtained were as follows:(1)The effects of ultrasonic power(160,320,480,and 640 W/cm~2)on the particle size,potential,intrinsic fluorescence,surface hydrophobicity,free sulfhydryl groups,infrared spectra,and apparent viscosity of whey protein microgel was investigated.Compared with whey protein microgel without ultrasonic treatment,with the increase of ultrasonic power,the potential and surface hydrophobicity of the microgel increased,which improved the stability of the microgel,reduced the particle size andα-helix content,and reduced the apparent viscosity of the suspension.(2)The cross-linking reaction between whey protein and tea polyphenol was affected by ultrasonic power(160,320,480 and 640 W/cm~2).The changes of particle size,potential,intrinsic fluorescence,total phenolic content,infrared spectra and apparent viscosity of whey protein-cha polyphenol composite microgel were investigated.The results showed that the covalent and non-covalent interactions between proteins and polyphenols were gradually enhanced with the increase of ultrasonic power.The crosslinking between whey protein and polyphenol increased the particle size and the absolute value of potential of the composite microgel,and transformed the secondary structure of the composite microgel into a more stable structure,which improved the stability of the microgel.(3)Microgel and composite microgel with different ultrasonic power(160W and480W)and without ultrasonic treatment were selected for the study to prepare casein mixed gels.By exploring the texture,water holding capacity,infrared spectrum,microstructure and rheological properties of the mixed gel,the influence on the mixed gel was studied.The results indicated that C-480W without the addition of polyphenols was the best overall.The mixed gel had higher hardness,better water holding capacity,soft and deformable characteristics.The hydrophobic interactions of the gels were enhanced,resulting in an ordered gel structure and a smaller void space in the gel network.This indicates that whey protein microgel can strengthen casein gels and exhibit some gel-assisting properties.(4)The emulsion was prepared by using whey protein microgel as emulsifier.Measurement of the particle size,potential,microstructure,apparent viscosity,emulsification activity,and emulsion stability of microgel stabilized emulsions.The results indicated that TE-640W with the addition of tea polyphenols exhibited the best emulsion stability.This is due to the increase in the absolute value of potential,which limits the mobility of emulsion droplets and hinders particles aggregation.In addition,the cross-linking between microgel and tea polyphenols increased the particle size of the complexes,which could form a more stable interface structure during the construction of emulsion system,leading to better emulsification performance.Whey protein microgel prepared by different preparation methods show better emulsifying properties and can broaden its application field.In conclusion,during the preparation of whey protein microgels,ultrasonic treatment can affect the structure and physicochemical properties of microgel,which in turn affect the functional properties of the microgel.This has an impact on the hardness,structure and water holding capacity of the hybrid gel.In addition,the addition of ultrasonic treatment in the preparation of whey protein-tea polyphenol composite microgel has a great influence on the emulsification of microgel and can significantly improve the emulsification stability of microgel.