Stability characteristics of O/W emulsions prepared using purified glycyrrhizin or a non-purified glycyrrhizin-rich extract from liquorice root (Glycyrrhiza glabra)

This study evaluated the stability characteristics of oil-in-water emulsions prepared using purified glycyrrhizin (PG) or a non-purified glycyrrhizin-rich extract from liquorice root (LRE) at equivalent glycyrrhizin concentrations (0.01−0.1%, w/w). PG-stabilized emulsions were sensitive to acidic pH (< 5), NaCl addition (≥ 50 mM), and freeze-thaw cycles. Consequently, they showed signs of droplet coalescence upon storage at these conditions and were prone to phase separation. LRE-stabilized emulsions, on the other hand, were more resistant to these storage stresses with no evidence of phase separation. They showed, however, extensive aggregation in extreme salt concentration (400 mM) and were sensitive to thermal processing (> 60 °C). These results indicate that the interfacial composition of the two studied systems was different although having similar glycyrrhizin concentration. PG-stabilized droplets consist of glycyrrhizin interfacial layers that are negatively charged and depend exclusively on electrostatic repulsion. LRE-stabilized droplets consist of complex interfacial layers due to the adsorption of various surface-active components, including glycyrrhizin and proteins.