Effects Of Pectin-Whey Protein Blends On The Stability Of Polyp Henols

Polyphenols have the function of scavenging free radicals and are good antioxidant substances.Introducing polyphenols into food system can improve the antioxidant and nutritional value of food,and protein is regarded as a good carrier for adding polyphenols into food system.However,polyphenols can bind to proteins through non-covalent bonds to produce adverse turbidity or colloidal turbidity.Pectin is an anionic polysaccharide,which is used as a stabilizer in the food industry.Whey protein-pectin complex is used to encapsulate nicotinic acid or control the release of functional components.In this study,the effects of protein-polysaccharide system on the stability of polyphenols were observed.The effects of polysaccharide-protein complex on the stability of polyphenols were studied by measuring turbidity,particle size,potential,surface hydrophobicity,fluorescence intensity and DPPH antioxidant activity under different environmental conditions.The results are as follows:(1)To compare the physicochemical indices of the complex formed by the interaction of pectin-whey protein and EGCG under heating and non-heating conditions.In this study,whey protein concentration was 0.5%,pectin content was 0.1%,0.2%,0.4% and 0.8%,respectively.The results showed that the turbidity value of heated samples was lower than that of non-heated samples.The particle size of whey protein-EGCG decreased from 158.3nm to 42.6 nm,and the particle size of whey protein-high methoxy pectin(0.8%)-polyphenol complex decreased from 747.7 nm to 178.1 nm.After heating,the potential value of whey protein-EGCG complex decreased from-15.07 m V to-17.0 m V,and that of whey protein-high methoxypectin(0.8%)-EGCG complex decreased from-19.47 m V to-21.67 m V,which proved that the electrostatic force of ternary polymer formed after heating increased,the system became more stable and the turbidity of particles decreased.Comparing the fluorescence spectra of two groups of samples before and after heating,it was found that the fluorescence intensity of the samples after heating decreased,which indicated that heating caused denaturation of whey protein and change of tertiary structure.(2)On the basis of heat treatment of pectin-whey protein complex,the changes of physical and chemical indexes of the system under different salt concentration were analyzed.Visual observation showed that the addition of high content pectin at low salt concentration would lead to stratified precipitation of the system,and the ternary polymer with high content pectin was not easy to precipitate at high salt concentration.The turbidity(particle size)of samples increases with the increase of salt concentration,and increases with the increase of pectin content at the same salt concentration.Due to the electrostatic shielding effect of salt,whey protein low methoxy pectin(0.1%)-polyphenol complex increased from-20.3 m V to-12.37 m V with the increase of salt concentration from 0 M to 0.4 M.Under the condition of 0 M Na Cl,the absolute value of potential increases with the increase of negative charge number of ternary polymer,and increases with the increase of pectin concentration under the condition of salt.At low salt concentration,electrostatic repulsion is the main stabilizing force in the system;at high salt concentration,the system can achieve stabilization through spatial repulsion or covalent bond,possibly because of the greater aggregation of proteins by high salt concentration.(3)The stability of the system was compared at p H 7.4 and p H 4.It was found that high content pectin could prevent precipitation in the system under acidic conditions,denaturation of whey protein under acidic conditions and high turbidity under weak alkali conditions.The turbidity value of ternary polymer decreased with the increase of pectin content,and the absorbance value decreased from 1.6248 to 0.7106.Because whey protein is positively charged in acidic condition,the potential of whey protein-EGCG is 14.43 m V,and the potential of ternary polymer decreases to-13.0 m V with the increase of pectin content.The results show that the electrostatic interaction plays an important role in the stabilization process.The results show that the addition of EGCG to the heated whey protein-pectin complex can reduce the turbidity of the ternary polymer,reduce the particle size,and increase the absolute potential,that is,increase the electrostatic repulsion force.The ternary polymers with different content of pectin exhibit different stability under different salt concentration.At low salt concentration,the ternary polymer with low pectin content has good stability and no delamination.The main reason is electrostatic repulsion.At high salt concentration,ternary polymer with high pectin content can prevent precipitation in the system,but its electrostatic repulsion force is relatively low,and the main force needs further study.Different p H has different effects on the stability of the system.The system is stable at p H7.4.Layering of whey protein-EGCG binary polymer occurs at p H 4.Adding high content pectin can effectively alleviate the delamination and make the system more stable.Increasing salt concentration and acidic conditions can increase the antioxidant activity of polyphenols.