The synthesis and functional properties of mono-, di-, tri- and tetra-saccharide oleates

Sugar-derived fatty acid esters are well-known, environmentally friendly emulsifiers. Despite this, the relationship between the size of the ester head-group and their functionalities remains unclear. This study describes the enzymatic synthesis and systematic evaluation of glucose, galactose, sucrose, lactose, raffinose and stachyose mono-oleate esters. The results reveal that increasing the sugar unit from a mono- to a tetra-saccharide one increased the hydrophilic-lipophilic balances (9.2 to 15.3), reduced critical micelle concentrations (1528 μM to 95 μM), improved interfacial activity, and accelerated diffusion rates ∼10-fold. While mono-saccharide oleates were poor emulsifiers, their di- to tetra- counterparts were good ones. A tri-saccharide oleate exhibited optimal performance, producing fine emulsions with a mean particle size of ∼570 nm. In addition, saccharide composition did not affect the shelf lives (≥ 20 days) or stabilities of the derived emulsions. This study identifies clear structure-function relationships, and so providing a valuable framework for the design of next-generation sugar-based surfactants.