Effects Of Protein Assemblies On Protein/Polysaccharide Electrostatic Complexation And Its Functional Properties

Electrostatic complexation of protein/polysaccharide has been widely applied in the food industry.Protein/polysaccharide complexes might create new processing properties which can provide more application in the food process field.However,the studies that compared systematically the interaction between different aggregates of proteins and polysaccharides were rather few.The protein/polysaccharide system of native granular ?-lactoglobulin(NGBLG)/?-carrageenan(?-car)was investigated in this study.The protein aggregates of varying molecular scales,such as nanoparticle ?-lactoglobulin(NPBLG)and fibrillar ?-lactoglobulin(FBLG),were prepared by adjusting pH and temperature.Firstly,the emulsifying,foaming and interfacial properties of ?-lactoglobulin and its aggregates were studied.Besides,the two-dimensional phase diagrams of NGBLG/?-car,NPBLG/?-car and FBLG/?-car mixtures(0.1%(w/w))were established.Finally,the gel properties,emulsifying properties,foaming properties and interfacial properties of electrostatic complexation between NGBLG and its aggregates and ?-carrageenan were studied.Therefore,the structure-activity relationship between protein aggregation state,protein/polysaccharide electrostatic complexation,interface behavior,and emulsification/foam properties could be established.The main conclusions are as follows:1.High purity NGBLG was extracted from fresh milk by isoelectric precipitation.NPBLG with a particle size of 350 nm and FBLG with a length of 500~700 nm were prepared by adjusting pH and temperature.The emulsification and foam properties of NGBLG and its aggregates were investigated at different pH.The results showed that FBLG and NGBLG exhibited good emulsifying properties and foam stability.The emulsification properties of NGBLG and its aggregates were more stable at pH=7.0.NGBLG and its aggregates exhibited good foaming ability and foam stability at pH=4.0.2.Under the acidification induced by GDL,the phase diagram of the protein/ polysaccharide system was established by measuring the change of turbidity,scattered light intensity and hydrodynamic radius with pH.The established phase diagram could be generally divided into four phase regions including soluble molecular region,intramolecular soluble complex region,intermolecular soluble complex region and intermolecular insoluble complex region,respectively.The results demonstrated that the aggregation state of NGBLG had not a significant effect on the phase region of the intramolecular soluble complex.In the intermolecular soluble complex region and the intermolecular insoluble complex region,the critical conditions for their formation were in the following: FBLG/?-car > NPBLG/?-car > NGBLG/?-car,which moved toward high pH and low mixing ratio.3.The effect of electrostatic complexation between NGBLG and its aggregates and polysaccharide to the gelation of polysaccharide was characterized by rheological measurement,micro DSC and micromorphology.The inhibition degree of NGBLG and its aggregates on the behavior of ?-carrageenan gel was affected by pH.There is no significant effect of NGBLG and its aggregates on gel behavior of ?-carrageenan at pH=9.0.However,NGBLG and its aggregates inhibited the gel behavior of ?-carrageenan at pH=4.0.Therefore,the viscoelasticity and rheological behavior of the protein/polysaccharide system can be effectively modified by controlling the aggregation state of the protein.4.In the soluble molecular region(pH=7.0),the emulsifying and foaming properties of NGBLG and its aggregate/?-carrageenan mixtures were strongly dependent on the proportion of NGBLG and its aggregates,and their emulsifying and foaming properties became better with the increase of mixing ratio.Furthermore,FBLG/?-car demonstrated optimal emulsifying and foaming properties.In the intramolecular soluble complex region(pH=4.0),NGBLG and its aggregate /?-carrageenan composites exhibited good emulsification and foam stability at lower mixing ratios.Simultaneously,combined with the interfacial properties,the FBLG and FBLG/?-car systems had high interfacial activity and could provide optimal emulsifying and foaming properties.