Structure Regulation And Digestion Behaviors Of Mixed Potato And Whey Protein Gels

In order to reduce carbon emissions,the development of nutritious and healthy food of mixed protein for using plant protein to partially replace animal protein has become a hot research topic in recent years.Potato protein（PP）not only has good processing properties such as gelation,but also has low relative molecular weight,low denaturation temperature and low sensitivity.Thus,potato protein has a great application prospect of partial replacement of animal protein to develop dual-protein gel products.Studies have shown that the structure of food gels can affect the release of nutrients such as protein and fat during digestion,resulting in changes in nutritional quality.Therefore,understanding the digestion behavior of gels plays an important role in reverse design of protein gel products with different functions and properties.This paper used whey protein（WP）as raw material for animal protein,investigated the effects of protein concentrations and ratios on potato and whey protein mixed gels properties,explored the influence of ultrasound regulating gels’structure on its digestive products characteristics and its chemical and cellular antioxidant activity,providing the basis for the design of new type nutritional and health dual protein gels.The main researches and results are as follows:（1）The solubility,sulfydryl content,particle size,potential zeta,rheological properties,gel chroma,texture（TPA）,water distribution,gel structural force,microstructure（CLSM,SEM）were used to investigate the different protein concentrations（4%,5%,6%,7%,8%）and the ratio（PP/WP,10:0,8:2,6:4,5:5,4:6,2:8,0:10）on the gel properties of composite protein.Potato protein can partially replace whey protein to form composite protein gel,which can significantly reduce the amount of whey protein and keep certain texture and water holding capacity of composite protein gel.The lowest gelling concentration of composite protein gel was 5%,and the protein concentration significantly affected the gel strength,viscosity,chewiness and bound water content of mixed protein gel.The protein concentration increased from 5%to 8%,the hardness of the mixed gel increased by 5.28 times（p<0.05）,which was 68.01±2.38g.The solubility analysis showed that the main forces maintaining the gel structure were hydrogen bond and hydrophobic interaction.The composite gel with total protein concentration of 8%（w/v）has good gel properties and dense network structure.The main secondary structures of mixed protein gels wereβ-sheet andβ-turn,accounting for about 70%.The results of protein ratio experiments showed that when the composite protein ratio was 5:5,the gel had better hardness,elasticity,high bound water content and compact microstructure.（2）The gel chroma,texture,water distribution,gel structural force,microstructure,free amino group and acid and base consumption as indicators,investigated the effects of ultrasound（single frequency 40 k Hz,15min;dual-frequencies 40/60 k Hz,7.5min;triple-frequencies 20/28/40 k Hz,5 min）assisted p H shifting treatment on potato protein and analyzed the properties of potato and whey protein mixed gels as well as the structure and digestive properties of gels.The results of gel properties and structure characteristics showed that ultrasound pretreatment improved the solubility of potato protein compared with the untreated samples.The sample treated by 40 k Hz ultrasound for 15 min,the solubility（79.40%）increased by 49.29%.Unlike the composite of potato protein and whey protein which was pretreated by ultrasound to form solid forming gel,the composite of potato protein and whey protein which was not pretreated by ultrasound formed semi-solid gel.The mixed protein gel has the highest energy storage modulus and higher bound water content in terms of water distribution while potato was treated by 40 k Hz ultrasound for 15min.There were no significant differences in texture,intermolecular force and protein secondary structure among the mixed protein gels with different ultrasound pretreatment（p>0.05）.Both potato protein and whey protein are involved in the formation of the gel.Hydrogen bond,hydrophobic interaction and disulfide bond all play a role in maintaining the potato and whey protein mixed gels’structure.The structure of the gel affects the digestion of the gel.The digestion kinetics of different complex protein gels can be described by a complex first-order kinetics equation including enzyme diffusion and enzymatic hydrolysis.（3）The antioxidant activity of potato and whey protein mixed gels simulated in gastrointestinal was used as an indicator.Through chemical methods for determining the digestion products antioxidant capacity(reducing power,DPPH and ABTS radical scavenging ability,hydroxyl radical scavenging ability,Fe²⁺chelating ability).The ROS content,the MDA and activity of antioxidant enzymes in Caco-2 cells were used to evaluate the mixed protein gels’gastrointestinal digestive products protective function of pretreated with different ultrasound-assisted p H shifting.The results showed that the digested products of potato and whey protein mixed gels had certain antioxidant activity.The digested products of gels,which were treated by ultrasound,enhanced the scavenging ability of DPPH free radical,hydroxyl free radical,ABTS free radical,reducing power and Fe²⁺chelating capacity.The ability of free radical scavenging was positively correlated with the concentration of the sample.The digestive products of the gel treated with dual-frequency 40/60 k Hz ultrasound for7.5 min had better free radical scavenging ability.The reduction power and Fe²⁺chelation ability of the digested products was stronger after the treatment with 20/28/40k Hz for 5 min.Caco-2 cells were induced to produce ROS by H₂O₂ induction,adding different digested products and we found the digestive products of mixed protein gels treated with dual-frequencies 40/60 k Hz ultrasound for 7.5 min had relatively better ROS scavenging ability.The digestive products of mixed protein gels could significantly increase the activities of GSH-Px,SOD and CAT and the levels of GSH in Caco-2 cells which was induced by H₂O₂,effectively remove ROS in Caco-2 cells,prevent lipid peroxidation,significantly reduce the content of MDA and carbonyl,and protect cells from H₂O₂ induced oxidative damage.The digestive products of the gel without ultrasonic treatment showed a lower satiety capacity,while the digestive products of the samples with ultrasonic treatment showed a higher satiety potential.After 7.5 min of dual-frequencies 40/60 k Hz ultrasonic treatment,the digestive products of the protein gel showed a better effect on promoting the secretion of GLP-1and CCK.These results indicate that,although ultrasonic pretreatment of potato protein has little effect on the gel properties of potato and whey protein mixed protein gels,it can affect the structure of mixed protein gels to regulate its digestion behavior and the cellular antioxidant activity of digested products.The results of this study provide a basis for the theory of gel structure regulating gel digestion behavior and provide guidance for the design of new nutritional mixed protein gel products.