| Sodium caseinate is an excellent protein with a typical amphiphilic structure, beingsurface-active, it can function as an effective protein emulsifier, which also easilycauses the emulsion building by protein unstable. we can add the polysaccharide intothe emulsion stabilized by proteins to enhance the stability because sodium caseinateis sensitive to the factors such as temperature, pH, ionic strength and so on, Fish oil isrich in EPA and DHA. However, the application is limited for its characteristics ofoxidative rancidity and oil soluble. In addition, if fish oil is made the form of oil/water,it’s an effective way to pass it to food. Thus, based on the CN-PGA interactions insolution, this paper explained the stability mechanism of PGA and CN in acidicconditions and the effect on the stability of fish oil emulsion. The main contents andconclusions are as follows:1、The rheological properties of the PGA solution and the influence of some factorswas investigated. The PGA solution possessed a thixotropic viscoelasticity, it’s atypical pseudoplastic fluid at higher concentration(＞1.0wt%). The viscosity ofsolution decreased with shear rate and temperature increased, increasded with thesucrose content. The viscosity decreased contrasted with the control under the lowerNaCl concentration(0.01M and0.1M) and increased at the higher NaClconcentration(1M).2、The interactions between CN and PGA were analyzed through plotting the phasediagram and measuring the turbidity, particle size, δ-potential and viscosity of theprotein-polysaccharide complex solution in combination with the use of confocal laserscanning microscopy. Under neutral conditions, the protein and polysaccharide whichcarried the same kind of net negative charge didn’t induce macroscopic phaseseparation when the sodium caseinate and propylene glycol alginate concentrationswere low（0.3wt%CN, PGA≤0.3wt%）. The protein-polysaccharide complex wasalso showed to be relatively stable under neutral conditions through microstructure observations; The phase separation was obvious under acidic conditions with a lowconcentration of PGA(≤0.075wt%). When increasing the concentration of thepolysaccharide to0.1wt%, the complex solution could become colorless andtransparent. The phase diagram indicating the PGA molecules could be adsorbed tothe surface of casein when pH was lower than5.5, the stability of the system wasmaintained mainly through steric effect for the electrostatic interactions between PGAand sodium caseinate was weak in combination with the analysis of micro-structurediagram and size, δ-potential. When pH was4, a low concentration of NaCl had aslight impact on the stability of the complex. When the concentration of NaCl reached100mM, the complex would become unstable as the electrostatic shielding effects ofsalt ions on the charged particles increased.3、The impact of PGA on the stability of oil/water(O/W) type fish oil emulsionstabilized by sodium caseinate was studied through measuring the size, δ-potential,protein adsorption at interface, microstructure etc. Under acidic conditions thestability of the emulsion was enhanced when PGA was added, the particle size wassignificantly reduced and the emulsion stability index and protein adsorption atinterface were low compared with the fish oil emulsion stabilized by sodium caseinatealone, this may be because the PGA molecules carried negative charge under acidicconditions, which made them be adsorbed onto the surface of droplets coated byproteins, the emulsion interfacial film thickness was increased and the electrostaticrepulsion between the droplets was enhanced. On the other hand the steric effectprovided by PGA effectively inhibited the accumulation of droplets caused by van derWaals attraction between them. The tolerance of emulsion to temperature was strongat pH4.0, the system was still stable under temperature within the range of30℃-90℃and became dissociated at120℃. The emulsion was quite stable at lower NaCIconcentration(＜100mM). When the concentration of NaCl was above100mM, thesystem became unstable as the emulsion particle size, the protein adsorption atinterface and the emulsion stability index increased significantly.The change of PV value and TBARS value of the emulsion during storage periodindicated that the PV value of the control began to increase sharply at the fourth day while the sample was at the twelveth day at the temperature of30℃, indicating theemulsion stabilized by the protein and the polysaccharide retard oxidation of the fishoil. The temperature has a great influence on the oxidation rate of emulsion, the PVvalues and TBARS value of the system stayed low during the storage at4℃. Theoxidation became faster as the temperature increased. Under the storage of50℃, theTBARS value of the emulsion increased rapidly at the4th day, indicating that the fishoil had been oxidized. |
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