The emulsification properties of alkaline-extracted polysaccharide conjugates from Apocynum venetum L. tea residues

Abstract

As a non-camellia tea with a rich history in Chinese culture that spans several centuries, Apocynum venetum L. tea is a brewed beverage made from the leaves of the Apocynum venetum L. plant. Despite its long history, little research on the polysaccharides in Apocynum venetum L. leaves has been conducted. In this study, polysaccharide conjugates were extracted from Apocynum venetum L. tea residue under alkaline conditions, referred to as ATPC-A. The conjugates comprised polysaccharide moieties covalently bound to protein. Oil-in-water (O/W) emulsions were prepared from the mixtures of the ATPC-A in water and medium-chain triglycerides (MCT). The mean particle diameter (MPD) (d3,2) of the ATPC-A-stabilized emulsions containing 2.00 wt% and 3.00 wt% ATPC-A increased from 0.47 μm to 1.94 μm and 0.37 μm–1.48 μm after storage at 25.0 °C for 10 days. The zeta potentials of the emulsions were also stable around −40.00 mV. Compared to a 5.00 wt% gum arabic (GA)-stabilized emulsion, the ATPC-A-stabilized emulsion containing 1.00 wt% ATPC-A and higher featured smaller particle sizes and stabilities compared to at lower ATPC-A concentrations. Between pH 2.0 and 8.0, the MPD (d3,2) of the ATPC-A emulsions ranged from 21.05 to 5.67 μm, while the zeta potentials ranged from −25.47 to −44.88 mV. Under different concentrations of metal ions (Na+ and Ca2+), the MPD (d3,2) of the ATPC-A emulsion increased from 13.61 to 29.55 μm between 0.10 and 0.50 mol/L Na+) and from 26.60 μm to 43.72 μm between 0.01 and 0.05 mol/L Ca2+. The absolute zeta potential dropped from 35.07 to 32.53 mV (Na+) and from 33.33 mV to 17.63 mV (Ca2+). These results highlighted the utilization of polysaccharide conjugates derived from Apocynum venetum L. leaves and provided a basis for the high-value utilization of Apocynum venetum L. tea residues.