Role of lecithin in oleogel formation: effect of organic phase and study of hybrid systems

The proposal of alternative routes for the conventional oil structuring represents an important topic, since conventional routes involve the formation of crystalline colloidal networks that usually are comprised of high levels of saturated and/or trans fatty acids. Oleogels are proposed as alternative because they promote gelation of liquid solvents through 3D network formation. Biological phospholipids (also called lecithins), in particular phosphatidylcholine, were evaluated with different solvents (hexadecane and medium and long chain triacylglycerol) to form oleogels. It was verified that among the studied solvents only hexadecane led to gel formation. The characterization of nano and microstructure and rheological (isothermal and non-isothermal conditions) were investigated. The effect of lecithin concentration and inclusion of water or citric acid (primers) to modify the system were also evaluated in order to optimize the mechanical properties of the gel. The understanding of the variables involved in oleogel formation in a model system was sought so that the production of oleogels with food grade components would be possible from this first stage. Therefore, hybrid systems in the presence of lecithin with other oleogelator(s) were proposed. The combination between lecithin and sterol(ester)s was investigated by small angle X-ray scattering, microscopy, differential scanning calorimetry, rheological and uniaxial compression tests. At nanoscale it was possible to observe that the building blocks were modified according to the addition of lecithin as well as the solvent type. Thermal and mechanical behaviours were also influenced by the presence of lecithin which led to the reduction of the melting temperature, a longer time required for crystallization and the apparent reduction of gel hardness. From these results we hypothesized that lecithin would dispute binding sites involved in the formation of complexes between ß-sitosterol and 'gama'-oryzanol, suppressing the formation of the typical fibrillar structures. However, still in the search for a synergistic system involving lecithin, a scanning with different types of waxes was performed. Among the waxes tested, fruit wax, which stands out for its unique composition (fatty acids and alcohols), showed promising results in oil structuring in combination with lecithin. The presence of lecithin affected the thermal behavior promoting a delay in the crystallization and gelation. An improvement in the mechanical properties (higher elastic modulus, tixotropy and oil binding capacity) at certain ratios between the components was observed when compared with the systems formed only with the wax. Moreover, lecithin affected the crystalline habit (size and shape) of fruit wax. In summary, this study initially had a fundamental approach based on understanding of lecithin as a main oleogelator, and a further investigation of more complex systems focusing in lecithin combined with other components also linked to nutritional and technological functionalities. Dissimilar behaviours of phospholipid either conferring greater plasticity or contributing to the hardness were reported as a result of the specific solubility balance of the system that leads to the success or failure to form gel. Unravelling the role of lecithin as a main or co-oleogelator brings the perspective of working with the engineering of ingredients in a rational and sustainable way (AU)