Study On The Relationship Between Microstructure Evolution And Macroscopic Properties Alteration In Supramolecular Oleogels

Owing to the fact that saturated fats and trans fats would be introduced during traditionalplastic fats hydrogenation process and their extremely adverse to human health, it is necessaryto find a new way to totally or partially replaced the traditional plastic fats, and more attentionswere focused on the liquid oil-based oleogels formed by edible oil gelators as potentialsubstitutes for traditional plastic fats. However, the narrow choose range for edible oil gelgelators greatly limited the application of oleogels in food industry. Therefore, this researchwas in view of the small molecular weight gelator without gelation ability when used alone inoil, and built a model to achieve gelation through changing stacked geometric structure ofgelator which then changed supramolecular network topology structure. Based on this model,rules of change in the multi-scale structure (crystalline, aggregated and supramolecular networktopology structure), and its association with the macro performances changes were discussed.From the perspective of the molecular structure of gelators and nutritional point of view,sitosterol and lecithin were selected as small molecular weight gelators, and gelled the vegetableoil, after that modern analysis technologies were used to study rules of change in the gelationmechanism, crystalline structure and macroscopic properties, as well as the macroperformances before and after the composite of different gelators. The results show that lecithininduced oil gelation via changing the stacked geometric morphology of sitosterol in oil. At thesame time, lecithin could increase the solubility of sitosterol in vegetable oil, which reducedthe crystal mismatch nuclear barrier of sitosterol, and promoted one dimensional growth ofcrystals, and eventually altered supramolecular network topology of oleogels. Moreover, thischange in the stacked assembly structure and the network topology further enhanced the macroperformances (such as texture, elasticity and thermoplastic, etc.) of oelogels.When the optimumcomposite mass ratio was obtained, the oil phase matrix which due to different levels ofunsaturation affected the interaction between composite gelators and oil phases, which resultedin different assembly structure, ultimately reflected on the macro-performance differencesbetween different oil-based oleogels. As unsaturation of oil phase matrix increased, it wouldbecome gradually difficult for the system to reach a supercooled state, and the gel formationtime needed for the system with higher unsaturated oil phase matrix would be longer. Moreover, the apparent viscosity of oleogels decreased with the increase of the unsaturation of oil phasematrix, which improved movement capacity of gelators in oil, and increased a highly assembledtendency of gelators along single axis, and finally led to the changes of assembled aggregationstructure and superamolecular network topology, and then enhanced the interaction between thebuilding elements in the network and increased the storage stability of oleogels.In addition, the microstructure evolvement (including assembled structure, aggregationstructure and supramolecular network topology, etc.) during the long-term storage at differenttemperatures and the changes of macro performance (e.g., texture, viscoelastic and thermalmechanical properties) had also been studied. The results showed that there was no significantchange in the elastic modulus (G) for the oleogels stored at low temperature during theextension of storage time. While storing at high temperature, SPC value and supramolecularnetwork construct unit size increased gradually, which made an increase in the number oftransient area formed between the building units, as well as an increase in the van der Waalsinteraction in the system, and finally resulted in the increase of G value with the extension ofstorage time. If the internal structure evolvement during the long-term storage at differenttemperatures was associated with the change of macro performance, a nucleation-growth-aggregation-growth mechanism for supramolecular self-assembly process in oleogel systemwas obtained.Structure changes of oleogel during the storage process had an effect on the oxidativestability of the oil entrapped in the system. Comparing with the control bulk oil,superamolecular network structure formed by gelators provided reaction interface for thecontact of oil and oxygen, and then promoted the primary oxidation reaction. Species andgenerated volume of the secondary oxidative product had a close connection with the fatty acidscomposition of the selected oil phase matrix, and the total secondary oxidative productgenerated volume (TSP value) for composite gelators-oil system was lower than for singlegelator-oil system. The TSP value for the gelled system was lower than its corresponding ofphysical mixed counterpart, this was because of a significant increase in apparent viscosities ofthe composite gelators-oil system or gelled vegetable oil-based oleogels reduced the diffusionability of oxidation reactants, which resulted in the reduction of probability of contact betweenthe lipid peroxy radicals, then reduced the formation rate constant of secondary oxidation products, and eventually led to a reduction of the generated volume of secondary oxidativeproducts, i.e., inhibited the secondary oxidation process of oleogels.This paper built a mechanism model based on the change of stacked geometric structure ofgelator induced oleogelation, and put forward a self-assembly growth model for oleogels, andmoreover, mastered the rules of change in different oleogel systems and in multi-scale structurechanges of oleogels during storage as well as its consequence on the physical properties, whichcould provide valuable basic data and theory for more reasonable design of oleogelators andguiding the processing and application of oleogels.