Preparation And Characterization Of Protein-based Transparent High Internal Phase Emulsions

In recent years,the researches related to high internal phase emulsions?HIPEs?have emerged endlessly.The research direction mainly focuses on the selection and development of high-efficiency stabilizers,the stabilization mechanism of stabilizers,and the application of HIPEs.Protein is one of natural organic materials that can be used as HIPEs stabilizers,and protein has many advantages such as wide sources,safety and health,also has many modification methods.In particular,some globular protein?such as ovalbumin,?-conglycinin?molecules containing sugar chains can stabilize HIPEs efficiently in the form of“soft particles”,because they have high structural stability.Inspired by this,the non-glycoproteins can improve the efficiency and properties of stabilizing HIPEs by glycosylation or adding polyols.But all the HIPEs stabilized by above stabilizers are turbid in appearance,so this paper attempts to develop a protein based HIPEs with special appearance characteristics—a transparent HIPEs.The key research findings are as follows:1.By adding the sucrose to BSA solutions can make the refractive index of solution close to the organic phase—n-dodecane,transparent HIPEs?internal phase volume fraction?=0.75?stabilized by BSA?BSA concentration c=0.5 wt.%?were successfully prepared,the light transmittance of transparent HIPEs exceeds 80%around wide wavelength range.Not only that,the adding of sucrose also changed the viscoelastic properties of BSA-based HIPEs,make their flow-like original to become gel-like finally,and the emulsification efficiency of BSA was improved greatly,the average surface area diameter(d_3,2)of the emulsion was reduced significantly and the minimum protein concentration of development gel-like HIPEs needed also decreased from 1 wt.%to 0.3 wt.%.All the changes caused by high concentration of sucrose solution added a“sugar shell”to the surface of BSA molecules,make BSA became a type of“soft particle”with“core-shell”structure,so BSA can be a Pickering HIPEs stabilizer with the help of sucrose.Not only BSA,but also other proteins?such as ovalbumin OVA,soybean 11S,sodium caseinate Na CS,and lysozyme LZM,etc.?have similar effects,indicating that this strategy has good protein universality.Therefore,this paper attempts to use a new protein with natural antioxidant properties—C-phycocyanin?C-PC?as transparent HIPEs stabilizer and try to exert its antioxidant activity effectively.2.Since there are no reports about the emulsification properties of C-PC in its natural state,before using C-PC to prepare HIPEs,this paper has a preliminary understanding of the emulsification properties of C-PC and focus on the effect of p H on emulsifying properties.The results showed that C-PC aggregation was more serious under acidic conditions?p H=3?,but fragmented under alkaline conditions?p H=11?,the protein structure was expanded,and the surface hydrophobicity was higher significantly than p H=5?9.Emulsification performance?particle size distribution,creaming index,interfacial adsorption capacity?at p H=3 and p H=11 in a low internal phase emulsion?soy oil as internal phase,c=1.0 wt.%and?=0.2?is better than other conditions.At the same time,in the HIPEs system??=0.8?,p H=3 and 11 conditions are also better than other p H conditions.However,under all conditions,HIPEs were unstable,because C-PC is a kind of polymer protein,and the structure may collapses at the interface due to the interfacial tension,resulting in the instability of interface.Therefore,the next step is to pre-depolymerize C-PC by urea to avoid emulsion instability caused by collapse of C-PC at the interface.3.The depolymerization effect of urea at different concentrations?0?8 mol/L?on C-PC was evaluated by various spectroscopic methods and finally selected urea concentration was 6mol/L,and it also retained the antioxidant capacity of C-PC in vitro.The addition of higher concentration?>4 mol/L?urea can avoid the instability of C-PC stabilized HIPEs effectively during storage.The addition of urea also reduced the dropsize significantly and made the size distribution more concentrated,while also enhancing the viscoelastic properties of HIPEs.Subsequently,the adding of glycerol on the basis of urea pre-polymerization also prepared transparent HIPEs,which further improved the emulsion-related properties.Thanks to the steric hindrance of HIPEs and the antioxidant activity of C-PC,C-PC based transparent HIPEs can protect?-carotene effectively under high temperature and ultraviolet irradiation.In summary,this paper successfully prepared protein-based transparent HIPEs by using sucrose or glycerol,provide theoretical guidance for the application of a new protein—C-PC in food emulsion products,and transparent HIPEs stabilized by C-PC can protect lipophilic bioactives effectively and have very broad application in potential.