The scientific and industrial communities have been giving great attention to the development of new bio-based materials with potential use in innovative technological applications. Among these materials are the structures with gel-like behavior that can be used in the cosmetic, pharmaceutical and food industries, aiming at controlling the physical properties of the final products. In the past ten years, words like oleogels and organogels have been increasingly used, the existing number of manuscripts and patents being proof of this tendency. In the food industry, oleogels can be used to control phase separation, and decrease the mobility and migration of the oil phase, providing solid-like properties without using high levels of saturated fatty acids as well as to be a carrier of bioactive compounds. In most cases, their main features are related to the reorganization process of gelators after an increase of the temperature, above the melting or glass transition temperature of the materials, known as the direct method, but it is also possible to develop oleogels by indirect methods, such as emulsification and the solvent exchange technique. In the direct methods, the reorganization is able to physically entrap oil leading to different physicochemical properties, the rheological behavior and texture properties being the frequently most studied ones. This review overviews the use of food grade and bio-based structurants to produce edible oleogels, aiming at fat replacement and structure-tailoring. Gelation mechanisms and oil phases used during oleogel production are discussed, as well as the current food applications and future trends for this kind of structure.

This work focused on how different types of oil phase, MCT (medium chain triglycerides) and LCT (long chain triglycerides), exert influence on the gelation process of beeswax and thus properties of the organogel produced thereof. Organogels were produced at different temperatures and qualitative phase diagrams were constructed to identify and classify the type of structure formed at various compositions. The microstructure of gelator crystals was studied by polarized light microscopy. Melting and crystallization were characterized by differential scanning calorimetry and rheology (flow and small amplitude oscillatory measurements) to understand organogels' behaviour under different mechanical and thermal conditions. Fourier transform infrared spectroscopy (FTIR) analysis was employed for a further understanding of oil-gelator chemical interactions. Results showed that the increase of beeswax concentration led to higher values of storage and loss moduli (G′, G″) and complex modulus (G*) of organogels, which is associated to the strong network formed between the crystalline gelator structure and the oil phase. Crystallization occurred in two steps (well evidenced for higher concentrations of gelator) during temperature decreasing. Thermal analysis showed the occurrence of hysteresis between melting and crystallization. Small angle X-ray scattering (SAXS) analysis allowed a better understanding in terms of how crystal conformations were disposed for each type of organogel. The structuring process supported by medium or long-chain triglycerides oils was an important exploit to apprehend the impact of different carbon chain-size on the gelation process and on gels' properties.

Hybrid gels can be used for controlled delivery of bioactives and for textural and rheological modification of foods. In this regard the hydrogel:oleogel ratio and gel development methodologies showed to be the aspects that influence most of their properties. The present study shows how different fractions of oleogel can influence the hydrogel matrix of an oleogel-in-hydrogel emulsified system in terms of polymorphic arrangement, microstructure, texture and rheology. The hydrogel was prepared by using an aqueous sodium alginate solution and the oleogel was prepared through the gelation of medium chain triglycerides with beeswax. Hybrid gels were prepared under constant shearing. Crystallinity was clearly changed as hydrogel and oleogel were combined. No polymorphism was observed in the X-Ray diffraction of hybrid gels, as these showed homogeneous results for all component ratios. The behaviour of samples with increasing oleogel-to-hydrogel ratio presented a decrease of both firmness and spreadability, and then, a decrease of gel adhesivity and cohesiveness. This textural response was a consequence of the disaggregated structure, stemming from the disruption of the hydrogel network, due to the inclusion of increasing amounts of oleogel. Rheological results showed that all hybrid gels presented a gellike behaviour (G´> G´´). Oleogel's strength influenced the overall textural and rheological performance of hybrid gels. This work demonstrates the possibility of producing hybrid gels aiming to tailor texture on food systems.

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