Effects Of Ultrasound Combined With Enzyme Pretreatment On Corn Gluten Meal And The Properties Of Zein Pickering Emulsion

As a by-product of corn starch processing,corn gluten meal contains about 60%protein with low protein purity and poor water solubility,which limits its wide application in the food industry.At present,it is mainly used as poultry feed,resulting in a large waste of protein resources.Ultrasound combined with enzyme pretreatment of corn gluten meal can break the binding between starch and protein by the cavitation effect produced by ultrasound,so that the?-amylase can better act on starch and improve the purity of protein.At the same time,the cavitation effect,mechanical effect and thermal effect produced by ultrasound can change the structure,spatial conformation and aggregation mode of proteins,and then cause the change of physical and chemical properties and functional properties of proteins.Therefore,this study used corn gluten meal as raw material,through studying the effects of ultrasound parameters and?-amylase enzymatic hydrolysis conditions on the protein content of c corn gluten meal,and established a method of ultrasound combined with enzyme pretreatment of corn gluten meal.At the same time,the changes of structure and functional properties of corn protein and zein(the main component of corn protein)after ultrasound combined with enzyme pretreatment were studied,and the relationship between structure and functional properties of corn protein and its main component was clarified.On this basis of pretreatment corn gluten meal,the nanoparticle formed by zein and the properties of Pickering emulsion were studied,in order to further reveal the effect mechanism of ultrasound combined with enzyme pretreatment on the zein Pickering emulsion,and to provide a theoretical basis for expanding the application of ultrasound technology and corn gluten meal in food industry.The main conclusions are as follows:(1)The influence of ultrasound combined with enzyme pretreatment on protein content in corn gluten meal was studied.The results showed that the highest protein content was 81.11%when ultrasound power density was 2.85 W/cm³,time was 35 min,temperature was 45?,pH6.0,and?-amylase added amount was 0.9%.At the same time,ultrasound combined with enzyme pretreatment could significantly shorten the action time of?-amylase.(2)The effects of ultrasound combined with enzyme pretreatment on the structure and functional properties of corn protein were studied.Compared with untreated corn gluten meal,the solubility,water holding capacity,oil holding capacity,emulsifying activity and emulsifying stability of corn protein after ultrasound combined with enzyme pretreatment were increased by 42.16%,106.35%,69.03%,23.71%and 22.36%,respectively.At the same time,the molecular weight of corn protein did not change significantly,but the particle size of corn protein particles decreased significantly,and the particle morphology changed.Fourier transform infrared spectroscopy analysis showed that the content of?-helix and random coil of corn protein was increased and the content of?-fold was decreased.After ultrasound combined with enzyme pretreatment,corn protein molecules were disfolded,the degree of conformational disorder increased,and the structure became more loose.The content of free sulfhydryl group in corn protein increased,and the content of disulfide bond decreased,which was caused by the disulfide bond breaking and the partial expansion of molecular structure.The internal groups of the protein are exposed,and the molecular flexibility is increased.(3)The effects of ultrasound combined with enzyme pretreatment on the structure and functional properties of zein in corn yellow powder were studied.The results showed that ultrasound combined with enzyme pretreatment of corn gluten meal could improve the extraction rate of zein in 80%ethanol and improve the purity of protein.The functional and structural properties of zein showed that the oil holding capacity and emulsification stability of zein were significantly improved after ultrasound combined with enzyme pretreatment,reaching 1.09 g/g and 42.92 min,respectively.Fourier transform infrared spectroscopy,ultraviolet spectroscopy and fluorescence spectroscopy of zein showed that the contents of?-helx and random coil in the secondary structural components of zein were significantly increased,while the contents of?-fold were significantly decreased.The ultraviolet absorption spectrum is enhanced,and?_max in the fluorescence spectrum is redshifted by 6 nm and the absorption intensity is increased.It shows that the internal groups of protein molecules are exposed and the structure is more relaxed.At the same time,the content of free sulfhydryl group in zein was increased and the content of disulfide bond was decreased after the corn gluten meal treated by ultrasound combined with enzyme pretreatment.(4)The effects of ultrasound combined with enzyme pretreatment on the properties of zein nanoparticles and Pickering emulsion were studied.The results showed that the zein nanoparticles were smaller in size,more uniform in particle distribution and higher in viscosity after ultrasound combined with enzyme pretreatment.The particle morphology of zein nanoparticles was spherical,and no obvious aggregation phenomenon was observed.The properties of zein Pickering emulsion were investigated.It was found that the type of emulsion was oil-in-water emulsion.In the ultrasound combined with enzyme pretreatment group,the Pickering emulsion particle size was smaller,the droplet size was more concentrated.This indicates that the dispersion of individual droplet is better and there is no obvious droplet aggregation.Meanwhile,when Pickering emulsion was stored at 25?,oil phase precipitated in the untreated group on the 4th day,while a very small amount of oil phase precipitated in the ultrasound combined with enzyme pretreatment group on the 6th day,and it remained stable at 4? for 15 days.The results provided theoretical support for expanding the application of corn yellow powder in food industry.