Protein-polyphenol Complexes Interaction And Their Effects On Protein Properties

Functional polyphenols play an important role in disease prevention and human health,and the combination of polyphenols and protein is commonly found in food digestion,processing and design.The digestive enzymes closely associated with diabetes(?-amylase-PPA,?-glucosidase-SCG),high nutritional milk proteins(?-lactoglobulin-BLG,lactoferrin-BLF),clean label attribute of high quality plant proteins(rice glutelin-RG,pea protein-PP)were selected as typical protein substances,meanwhile,phenolic acid(gallic acid-GA)and flavonoids(epigallocatechin gallate-EGCG,type A procyanidin dimer-PA2,type B procyanidin dimer-PB2,grape seed proanthocyanidin-GSP),stilbene(resveratrol-RES),tannin(tannic acid-TA)were also selected as typical polyphenols.The interaction of protein-polyphenol complexes and its influence on protein structure and functional properties were studied to provide theoretical basis and practical guidance for the design of functional food and new ideas of molecular processing.The main conclusions are as follows:(1)Research on the inhibitory effect of polyphenols on digestive enzymes and its inhibitory mechanism:the research system were PPA-PB2,SCG-PB2 and SCG-EGCG.Both PB2 and EGCG had better inhibitory ability to digestive enzymes,and their inhibitory ability were better than that of standard chemical(acarbose).The interaction of PPA-PB2,SCG-PB2 and SCG-EGCG were hydrophobic,hydrogen bond/hydrophobic and hydrophobic,and the number of binding sites were 0.8,0.8 and 1.0,at 37?,respectively.Meanwhile,the binding capacity of polyphenols and digestive enzymes were SCG-EGCG>PPA-PB2>SCG-PB2.When PB2 and EGCG were combined with the digestive enzymes,both of them can effectively quench the intrinsic fluorescence,reduce the surface hydrophobicity and change their secondary structure of digestive enzymes.PB2 made the ?-turn and random coil structure transformed to ?-helix and ?-sheet for the secondary structure of PPA,and PB2 did not change the ?-sheet,but made the ?-helix and ?-turn transformed to random coil.Similar to PB2,after the combination of EGCG with SCG,the EGCG made the ?-helix and ?-turn transformed to ?-sheet and random coil.These results may provide a theoretical basis for the development of food-grade anti-diabetes foods and the exploration/design of more effective digestive enzyme inhibitors.(2)Studies on the effects of polyphenols on the physicochemical properties of milk proteins and the interaction mechanism:the studied systems were BLG-PA2,BLF-PA2,BLF-TA.In terms of BLF foaming stability,PA2 and TA can bound to BLF hydrophobic interaction,making the foam stability of BLF increased,when the mass ratio of PA2/BLF(m/m)was 2/32,protein foam stability increased to a maximum of 124.9%,TA/BLF was 3/32,up to 150.6%,this may be due to polyphenols interacted with BLF at air/water interface and formed a thick viscoelastic interface membrane.In terms of BLF foaming stability,PA2 increased BLF foaming ability and had a dose-dependent relationship,when PA2/BLF was 2/32,foaming ability increased by 56.0%,but the TA made BLF foaming ability decreased and had a dose-dependent relationship,when the TA/BLF was 5/32,the foaming ability decreased by 73.5%,this may be due to the large molecular structure of TA hindered the rapid dispersion capability of BLF,then reduced its foaming ability.In addition,the effects of polyphenols(PA2,TA)on the binding capacity,surface hydrophobicity and secondary structure of milk proteins(BLG,BLF)were also studied.The results showed the binding capacity of TA(1.1 × 104 L/mol)to BLF was stronger than that of PA2(0.2× 104 L/mol),and BLG(0.8× 104 L/mol)to PA2 was stronger than that of BLF,at room temperature.Moreover,the combination of polyphenols with milk proteins decreased the surface hydrophobicity and changed the folding state of the proteins.Moreover,the PA2 changed the folded state of milk proteins(BLG,BLF)structure,with an increase of disordered structure.However,the TA did not change the disordered structure of BLF,just made the ?-helix and ?-sheet transformed to ?-turn.The results can provide theoretical basis for designing different functional and foam-based food.(3)Interaction between polyphenols and plant proteins and its application in O/W emulsion:the research systems were RG-GA,RG-PB2,RG-RES,and PP-GSP.Homologous modeling-molecular docking,isothermal titration calorimetry(ITC),and fluorescence spectroscopy were used to characterize protein-polyphenol interactions.The results showed that the self-assembly driving forces of RG-GA,RG-PB2,RG-RES,and PP-GSP were hydrogen bond,hydrophobic,hydrophobic,and hydrogen bond interactions,respectively.At room temperature,polyphenols had a strong binding capacity with plant proteins,and its binding constant was about 104 L/mol.The binding capacity GA-RG was the strongest and RES-RG was the weakest.In addition,due to the interaction between polyphenols and RG,the surface hydrophobicity of RG significantly reduced,and the secondary and tertiary structures of proteins significantly changed.The effects of polyphenols(PB2,RES,GSP)on the formation and stability of O/W emulsion stabilized by protein(RG,PP)were further investigated.The results showed that 0.02%PB2 had no significant effect on the appearance,microstructure,particle size and potential of RG emulsion;0.001%RES may interact with RG at the oil-water interface,making the particle size of RG emulsion and the microstructure size of oil droplets significantly increased,which may adversely affect the long-term storage stability of the emulsion.The combination of 0.3%GSP and PP changed the self-assembly capacity of PP,making the particle size of PP decreased.Compared with PP emulsion,the emulsion formed by PP-GSP was smaller in particle size and had better storage stability at 21 d.Besides,the emulsion was endowed with bright natural color.The above results can provide some theoretical basis and practical guidance for the design of functional,cleaning label emulsions and color rendering of emulsions.