Effects Of Molecular Weight Of Polysaccharides On Protein/Polysaccharide Electrostatic Complexation And Its Functional Properties

Proteins and polysaccharides have a wide range of functional characteristics and are widely used in food,medicine,biomedicial and other fields.Particularly in the food industry,proteins and polysaccharides,as typical biopolymers,have a wide application in the aspects of food emulsion and texture adjustment due to their basic characteristics of amphipathy and gelation.Electrostatic interaction is the main interaction between proteins and polysaccharides,and the complexes they formed enhibit more superior functional properties than single proteins and polysaccharides.The extrinsic factors affecting the electrostatic interaction of protein and polysaccharide mianly comprise mixing ratios(r),p H,ionic strength,total solids content and temperature,the intrinsic factories are related to molecular weight(Mw),net charge and flexibility of chains.In recent years,the researchs about external factors influcing protein and polysaccharide electrostatic interaction have been investigated widely,but the studies that systematically and comparatively explore the internal factors affecting the electrostatic interaction between proteins and polysaccharides have not been fully investigated.Thus,whey protein isolate(WPI)and sodium alginate(ALG)with different molecular weights were selected as research subiects in this study,and ALG of different molecular weights(8 k Da,15 k Da,20 k Da,70 k Da,120 k Da,170 k Da,230 k Da)was prepared through controlling the heating time,the effects of molecular weight of polysaccharides on the electrostatic recombination of proteins/polysaccharides and their food functional characteristics were finally studied.In this paper,the phase diagram of WPI and ALG with different molecular weights was first established in order to study the influence of molecular weights of ALG on WPI/ALG electrostatic complexation and deeply analyse their complexation mechanism.Based on the phase diagram of WPI/ALG and fixed the molecular weight of ALG,the foaming properties of different types of WPI/ALG(230 k Da)complexes were comparatively analyzed.Finally,the emulsification and foaming properties of WPI with ALG of different molecular weights on electrostatic complexation were studied.Therefore,the effect of the molecular weight of polysaccharides on the electrostatic conplexation of proteins/polysaccharides was investigated in the round.The main conclusions of this context are as follows:1.ALG with different molecular weights(8 k Da,15 k Da,20 k Da,70 k Da,120 k Da,170 k Da,230 k Da)was prepared through adjusting the time of heating through acid hydrolysis.Taking WPI and ALG of different molecular weights as the research objects,the changes of scattering intensity,turbidity and hydrodynamic radius with p H were measured through light scattering method under the acidification induced by GDL.The phase diagram of WPI and ALG of different molecular weights electrostatic complexation was established,and the influence of ALG molecular weights on WPI/ALG electrostatic complexation was analyzed by using molecular dynamics simulation.The results show that with the decrease of ALG molecular weight,the characteristic p Hc and p H? values of WPI/ALG electrostatic complexation in the phase diagram move towards the direction of higher p H values and lower protein/polysaccharide mixing ratios(r),which indicates that ALG of lower molecular weights is more likely to interact with WPI under the same p H conditions.Moreover,the smaller the molecular weight of ALG,the smaller the intromolecular soluble complex region in the WPI/ALG phase diagram.The result of molecular dynamic simulations shows that the effect of molecular weights of ALG on WPI/ALG electrostatic complexation is that ALG with smaller molecular weight has an edge on dynamics,leading to a higher probability to colloid with WPI.2.Based on the phase diagram established on chapter 1,the foaming properties(Foam capacity and foam stsbility)of WPI/ALG complexes were investigated systematically and comparatively.It is found at p H 4.0,the WPI/ALG intramolecular soluble complexes show the best foam stability around their maximum stoichometry,and its foam stability is much better that of other types of electrostatic complexes.Whereas at p Hs 7.0,and 0.5(the interaction between proteins and polysaccharides occurs),WPI mainly dominates the foam stability of WPI/ALG mixtures,namely as r increases,the foam stability is gradually improved,and WPI has the strongest foam stability.3.Based on the phase diagram of WPI/ALG(8 k Da,20 k Da,70 k Da,120 k Da,230 k Da)established,the effect of molecular weights of ALG on the foaming properties for WPI/ALG mixtures was analysed applying rheology and thermodynamic methods.It is finally found that when p H is 7.0(no electroststic complexation between proteins polysaccharides occurs),WPI/ALG(8 k Da?20 k Da?70 k Da?120 k Da,230 k Da)mixtures have the comparable foam capacity at the same r,which indicates molecular weights of ALG does not exert a positive effect on foaming properties of WPI/ALG mixtures when the electrostatic complexation between WPI and ALG does not occur.At p Hs 4.0 and 3.0(electroststic complexation between proteins polysaccharides occurs),WPI/ALG(8 k Da,20 k Da,70 k Da,120 k Da)shows the highest foam stability at r = 4,and WPI/ALG(Mw = 230 k Da)has the best foam stability at r = 1.It suggests that WPI has distinct binding ablity with ALG of different molecular weights.The foaming properties of WPI/ALG mixtures,therefore,can be effectively adjusted by changing the molecular weights of ALG.4.The emulsifying property of WPI/ALG(8 k Da,20 k Da,70 k Da,120 k Da,230 k Da)electrostatic complexation was investigated comparatively and systematically.The results show that when r = 4.0,WPI/ALG(8 k Da,20 k Da,70 k Da,120 k Da,230 k Da)complexes have different emulsifying activity and stability at different p Hs,and they exhibit the optimal emulsifying activity and stability at p H 6.0(no electrostatic complexation occurs between proteins and polysaccharides).When r = 1.0 and 0.25,WPI/ALG(8 k Da)complex show the best emulsifiing stability at p H 6.0(no electrostatic complexation occurs between proteins and polysaccharides),and WPI/ALG(20 k Da,70 k Da,120 k Da,230 k Da)complexes reveal the optimal emulsifying activity and stability at p H = 4.5(intramolecular soluble polymers region).