Gel Properties And Regulation Mechanism Based On Mixed Food Polysaccharide System

The extensive accessibility,non-toxicity and significant rheology-modifying properties of food polysaccharides enable them to be ideal starting materials for building and optimizing food structures.However,food polysaccharides are complex in nature,leading to their versatile rheological properties.At present,the rheology of food polysaccharides has not been deeply understood in China.In this thesis,we started in chapter one by summarizing the rheological properties of single food polysaccharide systems(including hydration,thickening,gelling and emulsifying properties,etc),and then we further discussed the typical phase behaviors of polysaccharide-based biphasic biopolymer systems.Subsequently,in chapter 2-5 we successfully fabricated a series of food gel structures with special textural properties,including high viscoelastic emulsion gels,double-network of konjac glucomannan(KGM)gels,thixotropic emulsion gels,and low-fat mayonnaise products,with mixture of KGM and xanthan,mixture of KGM and alginate sodium(Alg)and mixture of Alg and egg yolk as building materials,respectively.The physical properties and structural mechanisms of these gels were also investigated by means of rheology study and microscope techniques.The main results are summarized below:1)Preparation of high viscoelastic emulsion gels based on the synergistic gelation mechanism of xanthan and KGM.Both xanthan and KGM can be used as polysaccharide emulsifier to produce emulsions,but when preparing gel precursors,it was found that the mixing order of xanthan and KGM slightly affected the structuring mechanism and physical properties of the resulting emulsion gels.After introducing Tween-80 into the gel matrix,the thermal stability of the emulsion was greatly improved,with no discernible emulsion droplet coalescence observed after heating the emulsion gel at 121? for 30 min.Moreover,the synergistic binding between KGM and xanthan was found to be the dominant factor governing the gelation process of the emulsion matrix.Therefore,all emulsion gels exhibited similar gelation temperature(Tgel)and gel melting temperature(Tmelt),with Tgel=42? and Tmelt=44?,which was unaffected by the mixing order of KGM and xanthan,oil phase fraction and heating treatment.Furthermore,in the emulsion gels,the high viscoelasticity was well maintained,resulting from the dominant textural characteristics of the gelling continuous matrix(synergistic binding between xanthan and KGM).Taken together,these findings demonstrate that the emulsion gels have the potential to be used as a template to design functional gel foods for some special groups,such as the elderly and the like.2)Improved physical properties of KGM gels by co-incubating composite KGM/xanthan systems under alkaline conditions.When heating the composite KGM and xanthan systems under alkaline conditions(2.0%Na2CO3,90?),the presence of xanthan decreased the gelling rate of the KGM,with a higher xanthan content exerting a more pronounced effect.However,in the subsequent cooling procedure of the composite systems,it was found that xanthan synergistically bound with the KGM network,with the binding process beginning at 60?,independent of the mixing ratio of KGM to xanthan and xanthan concentrations.When the composite gels were cooled to 20?,the optimum synergistic ratio was found to be located at KGM/xanthan 7:3,and at this ratio,the gel strength was almost 30 times higher than that of the pure KGM gel(KGM/xanthan 10:0).Moreover,xanthan addition also decreased the syneresis rate of the composite gels during freeze-thaw treatment,with a higher xanthan concentration leading to a lower syneresis rate.3)Fabrication of thixotropic emulsion gels based on mixture of KGM and Alg.By adopting dilute solution viscometry(DSV),we found that both KGM and Alg showed molecular aggregation behavior in 0.1 M NaCl,as indicated by the discrepancy between their practical critical overlap concentration(0.2%for KGM and 0.25%for Alg)and the theoretically calculated values(0.95%for KGM and 0.3%for Alg).When the mixing ratio of Alg to KGM was lower than Alg/KGM 6:4,Alg and KGM can be considered compatible.By adding KGM into 4.0%Alg solution,we found the shear viscosity,viscoelasticity and thixotropy were significantly enhanced:a higher KGM addition yielded a stronger structure of the mixed matrix.Moreover,based on the mixture of Alg and KGM,a class of emulsion gels with significant viscoelasticity,thixotropic and spreadable properties were successfully prepared,and adding a small amount of calcium ions(0.15%CaCl2)further improved the structural strength,enabling the system to show the rheological properties very similar to those of a commercial low-fat mayonnaise product.4)Fabrication of low-fat mayonnaises based on electrostatic aggregation of Alg and egg yolk proteins at acidic pH conditions.It was found that the isoelectric point of egg yolk protein was located at pH 5.0.At pH<5.0,egg yolk proteins can form aggregates with Alg,whereas at pH>5.0,there was no aggregation occurring between egg yolk proteins and Alg.Addition of white vinegar also induced the electrostatic aggregation between Alg and egg yolk proteins,and a higher amount of white vinegar addition led to a more significant aggregation.Based on this result,a series of low-fat mayonnaises with 30%of oil phase fraction(v/v)were fabricated,where the emulsified oil droplets acted as dispersing phase and the aggregates of Alg and egg yolk proteins as continuous phase,both of which defined the structuring properties of the mayonnaises.At appropriate amount of white vinegar addition,the flavor and taste of the low-fat mayonnaises were significantly enhanced,but over-addition of white vinegar decreased the overall sensory acceptability.Therefore,at 4.0%(v/v)of white vinegar addition,it was found that the prepared low-fat mayonnaise showed better structural properties,taste,and flavor,when compared with the prepared high-fat mayonnaise(control).