Engineering Water-Induced Ceramide/Lecithin Oleogels: Understanding the Influence Water Added upon Pre- and Post-Crystallization

A mixture of ceramide and lecithin at specific ratios was capable of forming oleogels in sunflower oil triggered by adding trace amount of water. It was noted that the addition of water at different temperature (TW) resulted in different gelation behavior and microstructure. To better illuminate the assembly mechanism at different TW, samples with water added at different TW (20°C, 45°C, 70°C and 95°C) were prepared. The viscoelastic properties, microstructures, as well as the crystal packing of these samples were investigated. It was observed that all samples prepared at TW of 20°C and 95°C formed gels, while most samples prepared at TW of 45°C and 70°C were too weak to form gels. Gels prepared at 95°C are stronger but more fragile in texture compared to gels produced at 20°C. The crystal morphology of gels drastically changed with TW. Spindle-shaped crystals were observed in gels prepared at low TW (20°C). While gels prepared at high TW (95°C) exhibited a network with packed oil droplets stabilized by lamellar shells together with fibrillar crystals in the bulk phase. X-ray diffractogram showed a different reflection peak (d-spacing of 14.5 A) in gel prepared at 20°C, compared to the d-spacing in oleogels with single gelator (13.14 A and 15.33 A, respectively for CER and LEC). Gel prepared at 95°C showed two long spacing characteristic peaks, which correspond to the characteristic peaks of CER gel (~13 A) and LEC gel (~12 A). Fourier transform infrared spectroscopy results indicated that the different gelation behavior at different TW was mainly caused by vibrational changes in the amide bond of ceramide. Our hypothesized assembly mechanism can be concluded as: the increasing TW resulted in the conversion of CER and LEC crystallization from co-assembly (TW=20°C) to self-sorting by individual gelators (TW=95°C). In this study, novel water-induced oleogels were produced by manipulating TW, and such information further assists the rational design of lipid-based healthy fat products.