The role of small molecular weight surfactants on the mechanical and rheological properties of ethylcellulose oleogels

Abstract: Oleogels have raised great interest among food scientists as a promising approach for developing functional fat mimetics and alternatives to animal derived lipids with improved nutritional profiles. Ethylcellulose (EC) has shown promise as a directly dispersible polymer oleogelator, but these gels generally display limited plasticity due to poor solvent/polymer interactions. This work seeks to expand the scope of ethylcellulose as a functional oleogelator by characterizing the impact of incorporating various amphiphilic small molecule surfactants. Canola oil-based oleogels were prepared with 8 wt% EC (45cP) and a 2:1 EC/surfactant ratio. Seven surfactants were evaluated to contrast differences in the chemical structure of both the head and tail groups of these additives (Table 1). The addition of monoacylgolcerol (MAG), stearic acid (StAc), sodium stearoyl lactylate (SSL) and citric acid esters of monoglycerides (CIRTEM) enhanced the mechanical properties of the EC oleogels to varying degrees, with MAG and StAc having the greatest impact (Table 1, green cells). In contrast, diacetyl tartaric acid esters of monoglycerides (DATEM) diminished gel strength, but did not significantly impact the rheological behavior. CITREM produced the greatest enhancement in thixotropic shear recovery, and also produced a dramatic increase in strain stiffening in the large amplitude oscillatory shear (LAOS, Fig. 1) response. The latter was also observed with addition of SSL.
Preliminary FTIR results indicate the enhancement in gel strength is associated with a change in the EC hydrogen bonding network. The substantial impact of MAG, StAc and SSL may be attributed to the additional formation of a secondary crystalline network which directly interacts with the EC polymers. The molecular mechanisms by which these surfactants interact with the EC network and their roles in changing gel properties are continuing to be investigated and will be discussed in relation to developing functional polymer-based oleogel as fat mimetics.