Study On Emulsifying Properties Of Mixture System For Tilapia Protein And Soybean Protein

The Fish protein isolates (FPI), soy protein isolates (SPI) and tilapia-soy proteinco-precipitates isolates (Co-PI) were prepared by alkaline solution and isoelectricprecipitation from Tilapia muscle and defatted soybean meal. Effect of pH value, NaClconcentration and the type of polysaccharide on the emulsifying activity and stabilitywere discussed under the condition of different protein concentrations and oil volumefraction. The main purpose of this paper is to provide theoretical basis for developinghigh nutritional values, lower price and novel ‘double protein’ dairy products. The mainresults are as follows:(1) Effect of pH value and NaCl concentration on the emulsifying ability and stabilitywas studied for mixed protein emulsion system at0.5%of protein concentration. Theresults showed that the solubility, emulsifying ability and emulsifying stability of FPI,FPI-SPI (2:1), FPI-SPI (1:1) and SPI have the same trend with increased pH value(pH3.0-10.0). The minimum emulsifying activity and stability values were obtained atpH4.0~5.0, while the larger values were observed at pH3.0and10.0. FPI has the betteremulsifying activity at pH3.0(p<0.05), while emulsifying activity decreased withaddition of NaCl (range from0to0.4mol/L) for mixing protein system, and emulsifyingactivity of Co-PI was better at pH4.0,5.0and7.0. The emulsifying activity of all theprotein emulsion system increased with the increased NaCl concentration (0-0.4mol/L).(2) The emulsifying properties was improved by the addition of the xanthan gum,carrageenan, guar gum, apple pectin and chitosan for mixed protein emulsion system at0.5%of protein concentration and0.2%of polysaccharide addition. Comparatively,carrageenan and guar gum could significant improve emulsifying activity of the mixedprotein emulsion system, xanthan gum could significant improve emulsifying stability ofthe mixed protein emulsion system, but for the chitosan, the least effect for improvingemulsifying properties (p<0.05) was observed. The further study for effect of addition ofxanthan gum, carrageenan, guar gum on emulsifying properties under the condition ofpH3.0,4.0and7.0was also discussed. The results showed that the0.2%-0.3%additionof xanthan gum and carrageenan could obviously imporve the emulsifying properties ofthe mixed protein emulsion system (p<0.05) at pH4.0and7.0. For0.3%addition ofxanthan gum and carrageenan, the emulsifying activity index of FPI-SPI (1:1) was up to 62.97m2/g and64.60m2/g at pH7.0, respectively. Above all, xanthan gum andcarrageenan were selected as the additive for a further study on the emulsifying stabilityof mixed protein emulsion system.(3) The mixed protein system was prepared by high-pressure double-stagehomogenization (30MPa and4MPa) at pH3.0, and the effect of oil volume fraction(0.05-0.4) and protein concentration (0.1%-1.0%) on particle size distribution,microstructure and flocculation stability of FPI emulsion system was studied. The0.05ofoil volumn fraction and0.5%of protein concentration was determined for the furtherstudy, and the effect of the addition of xanthan gum and carrageenan on emulsionstability of protein emulsion system was discussed. The results showed that, at pH4.0,the mean particle size of protein emulsion system, droplet congregated and flocculationdecreased significantly with the increased addition of xanthan gum (0~0.09%), nocreaming was observed for emulsions after storage7d at4℃. At pH7.0,0.06%ofxanthan gum or carrageenan, the particle size of FPI-SPI (2:1)and FPI-SPI (1:1)decreased significantly (p<0.05), the micro flocculation was not improved obviously, andthe macro flocculation stability was increased significantly (p<0.05). For this emulsionsystem no creaming was observed for emulsions after storage10d at4℃. Comparatively,xanthan gum was more effective for controlling the micro flocculation of the mixedprotein emulsion system.(4) For further study on the rheological property of highly concentrated emulsionsystem, high protein concentration and oil volume fraction was used. Effect of oilvolume percentage (0.2~0.4), protein concentration (2%~4%) and pH (3.0~12.0) on theemulsion viscosity (η), dynamic elastic modulus (G’) and viscous modulus (G′′) wasdetermined. Results showed that the emulsion of each test system are shear thinningphenomenon in the shear rate range from0.01to200s-1, η value decreases rapidly withincreasing shear rate. In the heating process, the test emulsion system of elastic modulusincreases with increasing temperature, and G’ value was significantly greater than G’’value, indicating that the system tends to form a viscoelastic heating-induced protein gelemulsion. In the range of the study, when the oil amount of increase from20%to30%,the emulsifying system may be transformed from the O/W type to a W/O type, and the ηand G’ value increased obviously. For1%and3%of protein concentration η value washigher than that of2%emulsifying system, G’ increased with increasing proteinconcentration. At pH7.0and9.0, η and G’ value was larger for mixing protein emulsionsystem, while at pH3.0, η and G’ values were minimum for FPI-SPI (1:1) mixturesystem. In comparison, the thermal stability of highly concentrated emulsion system for tilapia protein-soy protein (1:1) mixture was better than that of FPI.