Quantitative Analysis Of The Amphiphilic Properties Of Casein Peptides And The Research On Emulsifying Properties Of Polysaccharide Grafts

Covalent modification of hydrophilic polysaccharide with hydrophobic peptides can improve the polysaccharide’s emulsifying properties, hence the quantitative analysis on amphiphilic properties of hydrophobic peptides is important. In this experiment, casein hydrolyzed peptide(CHP) was prepared and selected as a model peptide, the various apparent amphiphilic properties of CHP were studied for the correlation analysis. As the verification of CHP modification, Acacia seyal polysaccharide(Sy) was employed as a polysaccharide model and covalently attached to CHP through dry-state Maillard reaction to obtain a new polysaccharide emulsifier. Taking Acacia senegal gum(Sn) and Sy as references, the surface physical and chemical properties, their stability in O/W emulsion and preliminary study of the relationship between amphiphilic nature and emulsion performance were investigated. The main content and conclusions were summarized as follows: 1. The amphoteric properties of casein hydrolyzed peptides were analyzed quantitatively using the partition coefficient(K), transfer gibbs free energy(ΔG) in two phase(nbutanol/water), surface hydrophobicity(So) and average hydrophobic value(Hav). The results indicate that K, ΔG and So was negative correlated to degree of hydrolysis(DH), while Hav was positive correlated to DH. 2. Throgh extration by n-butanol, CHP with the DH of 1.5%, 5%, 10%, 15% and casein(DH 0) were screened out as the raw materials to carry on the grafting reaction with Sy. The conjugates of Sy CHP(DH 1.5%), Sy CHP(DH 5%), Sy CHP(DH 10%), Sy CHP(DH 15%) and Sy Casein(DH 0) were prepared at the optimum condition of Maillard reaction(60 oC, 75% RH, p H 7.0, three days, m CHP/m Sy=1:3). Taking Sn and Sy as references, the surface physical and chemical properties of the conjugates were investigated. It was found that the ability of the conjugates to reduce the surface/interfacial tension and interfacial viscoelasticity are stronger than that of Sy and decreased with creasing DH. The emulsion capacity in acidic emulsion of canola oil in water was up to 46-folds of that of Sy and closed to that of Sn, and the emulsion stability could be increased by 21-folds. 3. The effect of Sy CHP conjugates on the stability of the emulsion was investigated through the analysis of particle size. The results show that the ability of Sy CHP to stabilize the emulsion was in the order of Sy CHP(DH 1.5%) > Sy CHP(DH 5%) > Sy CHP(DH 10%) > Sy CHP(DH 15%) > Sy Casein(DH 0) > Sy. Sy CHP(DH 1.5%) was chosen as the emulsifier in O/W emulsion and found that the particle size of emulsion were less than 5μm after 28 days of storage at p H4.0, 85 oC and in the presence of 0.5 mol/L Na Cl. After the removal of unreacted CHP, the emulsion performance of Sy CHP was positive correlated to the hydrolyphobicity. And the emulsion stability of Sy CHP conjugates was improved compared to the unpurified ones, especially the Sy CHP(DH 1.5%). The emulsion stability was improved by 9.58%, and the particle size of emulsion with Sy CHP(DH 1.5%) reduced 1 μm after 28 days of storage.