Physicochemical Properties And Digestion Behavious Of Potato Protein And Whey Protein Mixture Fabricated Emulsions And Their Filled Whey Protein Gels

Potato protein is the derived from the by-product of the potato starch industry,but its application is limited in the food field due to its low solubility.Potato protein is rich in resources and has high nutritional value.Modification to improve its solubility is conducive to exerting the functional properties of potato protein and improving its application value in the field of food.This paper improved the solubility of potato protein by synergistic treatment of medium temperature,ultrasound and pH-shifting.The structure and digestion characteristics of potato protein were studied,and it was compounded with whey protein to control the physicochemical properties and digestion characteristics of complex protein emulsion and complex protein emulsion filled gel.The main research and results were summarized as follows:(1)The solubility was used as an indicator to investigate the effect of single treatment of medium temperature(40 °C),ultrasound(ultrasound mode,frequency,time)and pH-shifting(pH12)and different combinations.Circular dichroism spectroscopy,endogenous fluorescence spectroscopy,and atomic force microscope were used to investigate the effect of synergistic treatment of medium temperature/ ultrasound and pH-shifting on the structure of potato protein.It was found that the synergistic treatment of the above three modification methods can significantly improve the solubility of potato protein(p<0.05).Among them,the effect of ultrasound(40 kHz)for 15 min during the pH-shifting of 40°C was the most significant.And its solubility reached 87.0%,which was 173.3% higher than the control.The structural analysis results showed that the secondary and tertiary structure of the potato protein was significantly changed by the synergistic treatment of the three modification methods.Compared with the control,ultrasonic treatment(40 kHz)for 15 min during pH-shifting at 40°C has the greatest effect on potato protein structure.Under this method,the content of ?-helix structure in potato protein decreased by 56.7%(p <0.05),and the content of ?-sheet structure increased by 34.8%(p <0.05);Tryptophan endogenous fluorescence intensity increaseed by 17.4%(p <0.05),and the maximum emission wavelength was red-shifted;The total thiol content decreased by 30.0%(p<0.05),the free thiol content increased by 6.2%(p> 0.05),and the surface hydrophobicity decreased by 16.8%(p<0.05).The above results indicated that some protein molecules may aggregate.Moreover,the microstructure and electrophoresis results showed that the average particle size of potato protein molecules increased by 26.44%(p <0.05),the protein molecules formed large soluble aggregates,and the protein was in a molten ball state.(2)The effect of synergistic treatment of medium temperature/ ultrasound and pH-shifting on potato protein digestion characteristics was investigated,according to the content of free amino groups and the degree of protein degradation.It was found that synergistic treatment of medium temperature/ ultrasound and pH-shifting can improve its digestion characteristics.Potato protein was digested faster in the first 20 minutes of gastrointestinal digestion stage.When the sample was treated with ultrasound(40 kHz)during pH-shifting for 15 minutes at 40°C,it was found that compared with the control,the content of free amino groups and digestion rate in gastric digestion stage increased by 20.6% and 34.7%,respectively.And in terms of intestinal digestion stage,they increased by 24.7% and 17.1%,respectively.There was a notable positively correlation between the digestibility of potato protein and solubility(p<0.01).And the synergistic treatment of medium temperature/ ultrasound and pH-shifting produced soluble large aggregates,which were easier to digest.(3)The rheological properties,emulsification activity,emulsification stability of the interfacial membrane,particle size,surface potential and microscopic morphology were studied to analysis the effect of the ratio of potato protein(PP)to whey protein(WP)on the emulsification and physicochemical properties of the emulsion.The free amino content?free fatty acid content and single free fatty acid content were chosen as indicators to investigate the effects of different compounding ratios of PP and WP on the digestion characteristics of the emulsion.It was found that when the mass ratio of PP to WP was 10:0(PP:WP = 10:0),the complex protein had the strongest ability to reduce surface tension,and it was adsorbed to the interface membrane faster,and the emulsion has the best emulsifying activity;Althout the maximum particle size of emulsified droplets was 897.1 nm(p<0.05),the absolute value of the potential was the smallest 23.67 mV(p<0.05),the interface viscoelasticity was poor,but the interface adsorbed protein content was highest 11.44 mg / m2(p <0.05),apparent The viscosity was the largest,and the laser confocal microscope observes that the interface film was the thickest and the emulsion stability was the best.The emulsifying activity of the composite protein may be related to the surface tension,and the physical stability of the emulsion prepared by the composite protein may be related to its apparent viscosity and the particle size,surface charge,and interface properties of the emulsified particles.Whey protein had a higher digestion rate during simulated gastric digestion stage,but was more conducive to potato protein digestion during intestinal digestion.When PP: WP = 0: 10,the digestion rate of fats and oils was faster,but there was no significant difference in the final fatty acid release of all samples.(4)To study the influence of the effects of emulsified particles with different interfaces on gel properties of whey protein in different conditions(with or without Nacl),we detected the rheological properties,texture,water holding capacity,water distribution,swelling ratio and micro-morphology of the gel filled with emulsion particles.In addition,the effects of emulsified particles with different interface composition on the digestion characteristics of whey protein gel under different environments(with or without NaCl).The research results showed that emulsion filling can improve the gel structure and gel properties of whey protein gel.Sodium chloride can further improve the gel structure and gel properties of whey protein gel.Among them,under the condition of 50 mmol / LNaCl,PP: WP = 10: 0 emulsion filled whey protein gel had the best gel structure and gel properties.Compared with non-filled gel gels,the viscoelasticity of the gel can be enhanced,the gel strength was increased by 1291.7%(p <0.05),the water holding capacity was increased by 4.6%(p> 0.05),but the swelling capacity was reduced by 61.2%.The microstructure showed that the emulsion particles played a physical supporting role in the whey protein gel.The chemical force results indicated that potato protein and whey protein were mainly combined by hydrogen bonding and hydrophobic interaction.The release amount of fatty acid and protein digestion degree of emulsion-filled gel were related to gel characteristics.PP: WP = 10: 0 emulsion-filled whey protein gel had the lowest free fatty acid content and free amino content.In summary,synergistic treatment of medium temperature/ ultrasound and pH-shifting on potato protein can significantly improve protein solubility and digestibility.Potato protein may improve the stability and digestion characteristics of the complex protein emulsion by improving the interface properties of the emulsion interface.Potato protein may be combined with whey protein in the gel network structure to improve the gel characteristics and digestion characteristics of the emulsion particle filled gel.