Emulsifying Performance of Crude Surface-Active Extracts from Liquorice Root (Glycyrrhiza Glabra)

Abstract

The emulsifying performance of crude aqueous–ethanolic extracts from liquorice root (Glycyrrhiza glabra) (LREs) was investigated. Seventy five percent aqueous ethanol extract produced the most stable oil-in-water emulsions, with average volume mean droplet diameters of approximately 130 nm and monomodal size distributions. The extract contained 6.87% proteins, 7.99% saponins, and 6.72% polyphenols and reduced the interfacial tension from 25.3 to 12.0 mN m–1 at the soybean oil/water and soybean oil/extract (1%, w/w) interfaces, respectively. The emulsifying performance of LREs was not correlated, however, with their interfacial activity or surface-active composition. The water extract provided limited stability upon storage at 25 °C for 48 h, despite its important surface-activity and composition. This extract presented the highest electrical conductivity and the lowest ζ-potentials, indicating that electric screening of charges was occurring when it was used as an emulsifier. Our findings indicate that crude surface-active extracts can be used directly as emulsifiers, without further purification, provided that an accurate balance between emulsion stabilizing and destabilizing agents is achieved by extraction.