Engineering water-induced ceramide/lecithin oleogels: understanding the influence of water added upon pre- and post-nucleation.

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