Effect of pH on the Emulsifying Activity of C-phycocyanin
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Abstract:
The effect of pH on the physicochemical properties and emulsifying characteristics of C-phycocyanin (C-PC) was examined. The physicochemical properties of C-PC at different pHs (3, 5, 7, 9, 11) were determined through examining C-PC’s solubility, surface potential (ζ), surface hydrophobicity (H0), spectroscopic behaviors, and surface features (by transmission electron microscopy (TEM)). Using C-PC as an emulsifier and soybean oil as the oil phase, emulsion (oil ratio φ=0.2) was prepared, and the oil droplet size distribution, extents of flocculation and coagulation, creaming index and oxidation products were be determined to evaluate the effect of pH on the emulsifying properties of C-PC. The results showed that the 1 wt% C-PC solutions all had good solubility in the experimental pH range (minimum solubility: 69.15%); At pH 3 or 11, the C-PC polymer would depolymerize, with the peptide chains unfolding and the surface hydrophobicity increasing significantly. H0 was 200~650 at pH 5~7, whereas, the H0 values were 1703 and 1261 at pH 3 and 11, respectively. Therefore, at pH 3 or pH 11, emulsification was achieved to a greater extent along with smaller particle size and higher storage stability. The emulsifying ability of C-PC at other pHs was relatively low and the corresponding emulsion was unstable. In addition, oil oxidation was inhibited in all of the C-PC emulsions at different pHs, but slightly greater inhibition of oil oxidation was achieved at pH 5~9 than at pH 3 or 11. As shown in this paper, C-PC exhibits good emulsifying properties at acidic and alkaline pHs and possesses superior antioxidant activity, therefore, has the potential to be a natural and antioxidative emulsifier.
