Effect of metal ions and pH on the emulsifying properties of polysaccharide conjugates prepared from low-grade green tea

Polysaccharide conjugates were water-extracted from low-grade green tea; this extract was designated as TPC-W. Various concentrations of TPC-W (0.5, 1.0, 1.5, 2.0, and 3.0 wt%) were then used as an emulsifier stabilize to oil-in-water emulsions prepared using medium chain triglycerides. The emulsion stabilized using 2.0 wt% TPC-W remained relatively constant during 10 days of storage at 25 °C, with the mean particle diameter (MPD) (d32) and zeta potential increasing from 1.8 to 2.4 μm and from −19.8 to −18.9 mV, respectively. The effect of metal ions (Na+, Ca2+, and Al3+) and the pH value on the stability of the 2.0 wt% TPC-W emulsions was also studied at 25 °C for 10 days. The system remained stable at Na+ concentrations between 0.10 and 0.50 mol/L and Ca2+ concentrations below 0.030 mol/L, with little change in the MPD (d32) of the emulsion droplets. When Al3+ was added to the emulsion system, the MPD (d32) of the emulsion changed significantly; the addition of 0.001 mol/L Al3+ increased the MPD (d32) from 2.2 to 5.8 μm. The MPD (d32) of 2.0 wt% TPC-W emulsions with pH values of 2.0–4.0 increased significantly during the storage period, but remained stable for emulsions in the pH range 5.0–8.0. The results revealed new applications of TPC-W extracted from low-grade green tea as an emulsifier.