Properties and Stability of Perilla Seed Protein-Stabilized Oil-in-Water Emulsions: Influence of Protein Concentration, pH, NaCl Concentration and Thermal Treatment

Abstract

Perilla seed protein (PSP) was extracted from defatted perilla seed meal and applied in oil-in-water (O/W) emulsions as an emulsifier. We investigated the influences of protein concentration (0.25⁻1.5 wt %), pH (3.0⁻9.0), NaCl concentration (0⁻350 mmol/L) and thermal treatment (70⁻90 °C, 30 min) on the physical characteristics of O/W emulsions, including volume-average diameter, ζ-potential, interfacial protein concentration, microstructure and so on. Results showed that increasing PSP concentration would decrease the d_4,3 and a 1.0 wt % PSP concentration was sufficient to ensure the stability of emulsion. Under pH 3.0⁻9.0, emulsions were stable except at pH 3.0⁻5.0 which was proximal to the isoelectric point (pH 4.5) of PSP. At high NaCl concentrations (250⁻350 mmol/L), the emulsions exhibited relatively lower absolute ζ-potential values and a large number of aggregated droplets. A moderate thermal treatment temperature (e.g., 70 °C) was favorable for the emulsion against aggregation and creaming. However, when 90 °C thermal treatment was performed, a clear layer separation was observed after 2 weeks storage and the emulsion showed a poor stability. The findings of this work are of great importance for the utilization and development of PSP as an emulsifier for food emulsions.

Keywords: NaCl concentration; O/W emulsion; pH; perilla seed protein; thermal treatment.

Figure 1

pH-solubility curve of Perilla seed protein (PSP). Values are means ± SDs (n = 3).

Figure 2

Influence of pH on ζ-potential (●) and d_4,3 (○) of PSP-stabilized emulsions. Insets show the confocal laser scanning microscopy (CLSM) microstructures at (a) pH 5.0, (b) pH 7.0. Scale bar in the micrographs corresponds to 10 μm. Values are means ± SDs (n = 3).

Figure 3

Phase diagram of PSP in aqueous solution.

Figure 4

Influence of salt concentration on ζ-potential (●) and d_4,3 (○) of PSP-stabilized emulsions. Insets show the CLSM microstructures at (a) 50 mmol/L NaCl, (b) 150 mmol/L NaCl and (c) 250 mmol/L NaCl. Scale bar in the micrographs corresponds to 10 μm. Values are means ± SDs (n = 3).

Figure 5

Differential scanning calorimetry (DSC) analysis of PSP.

Figure 6

Influence of thermal treatment on the particle-size distribution and CLSM of PSP-stabilized emulsions. (a) the control (emulsion without thermal treatment), (b–d) emulsions with thermal treatment at 70 °C, 80 °C, 90 °C for 30 min, respectively. Scale bar in the micrographs corresponds to 10 μm. Values are means ± SDs (n = 3).

Figure 7

Influence of thermal treatment on the CI and creaming stability of PSP-stabilized emulsions. (a) the control (emulsion without thermal treatment), (b–d) emulsions with thermal treatment at 70 °C, 80 °C, 90 °C for 30 min, respectively. Values are means ± SDs (n = 3).