Crystalline stability of self-assembled fibrillar networks of 12-hydroxystearic acid in edible oils

12-hydroxystearic acid-mediated in-situ surfactant generation: A novel approach for organohydrogel emulsions

HYPOTHESIS

Organohydrogel emulsions display unique rheological properties and contain hydrophilic and lipophilic domains highly desirable for the loading of active compounds. They find utility in various applications from food to pharmaceuticals and cosmetic products. The current systems have limited applications due to complex expensive formulation and/or processing difficulties in scale-up. To solve these issues, a simple emulsification process coupled with unique compounds are required.

EXPERIMENTS

Here, we report an organohydrogel emulsion based only on a low concentration of 12-hydroxystearic acid acting as a gelling agent for both oil and water phases but also as a surfactant. The emulsification process is based on in-situ surfactant transfer. We characterize the emulsification process occurring at the nanoscale by using tensiometry experiments. The emulsion structure was determined by coupling Small Angle X-ray and neutron scattering, and confocal Raman microscopy.

FINDINGS

We demonstrate that the stability and unique rheological properties of these emulsions come from the presence of self-assembled crystalline structures of 12-hydroxystearic acid in both liquid phases. The emulsion properties can be tuned by varying the emulsion composition over a wide range. These gelled emulsions are prepared using a low energy method offering easy scale-up at an industrial level.

Influence of the Mixtures of Vegetable Oil and Vitamin E over the Microstructure and Rheology of Organogels

Candelilla wax (CW) and 12-hydroxystearic acid (12HSA) are classic solid-fiber-matrix organogelators. Despite the high number of studies using those ingredients in oily systems, there is scarce literature using a mixture of oil and antioxidants. Vitamin E (VE) is an important candidate for its lipophilicity and several applications on pharmaceutical, cosmetics, and food industries. In this work, we investigated the influences of mixtures between vegetable oil (VO) and VE on the microstructures and rheological properties of CW and 12HSA organogels. A weak gel (G′′/G′ > 0.1) with a shear-thinning behavior was observed for all samples. The presence of VE impacted the gel strength and the phase transition temperatures in a dose-dependent pattern. Larger and denser packed crystals were seen for 12HSA samples, while smaller and more dispersed structures were obtained for CW organogels. The results obtained in this work allowed the correlation of the structural and mechanical properties of the organogels, which plays an important role in the physical-chemical characteristics of these materials.

Vitamin E-loaded bigels and emulsions: Physicochemical characterization and potential biological application

Bigels have been studied as topical formulations for its benefits over sensory and drug delivery parameters. However, there is still few evidences about the properties of the combination of organogelators, oily phases and bioactive molecules into rheological and stability behavior. We investigated the use of classical organogelators (candelilla wax and 12-hydroxystearic acid) and oily phases (sunflower and mineral oil) in 5/95 organogel/polymeric hydrogel ratio to compare vitamin E bigels with its corresponding emulsions. The rheological measurements, microstructure, physical and oxidative stability properties and biological behavior were evaluated. The obtained oil-in-water bigels and emulsions showed crystallization pattern at the interface with high thermal and centrifuge-stress stability. Viscoelastic weak gels were obtained with higher thixotropy and consistency of 12-hydroxystearic bigels. The diameter of the inner phase was increased by vitamin E, despite its little influence over physical and oxidative stability of bigels and emulsions. Those findings indicated that sensory attributes may be regulated by the organogel composition.

Preparation of Protein Oleogels: Effect on Structure and Functionality

Among available structuring agents that have been used to provide solid properties to liquid oils, protein is a more recent candidate. Due to their nutritional value and high consumer acceptance, proteins are of special interest for the preparation of edible oleogels as an alternative for solid fats. Whereas the field of protein oleogelation is still rather new and just starts unfolding, several preparation methods have been demonstrated to be suitable for protein oleogel preparation. However, there is limited knowledge regarding the link between microstructural properties of the gels and macroscopic rheological properties, and the potential of such protein-based oleogels as a fat replacer in food products. In this review, we therefore provide an overview of various protein oleogel preparation methods and the resulting gel microstructures. Based on the different structures, we discuss how the rheological properties can be modified for the different types of protein oleogels. Finally, we consider the suitability of the different preparation methods regarding potential applications on industrial scale, and provide a short summary of the current state of knowledge regarding the behavior of protein oleogels as a fat replacer in food products.

Role of the oil on glyceryl monostearate based oleogels

The high consumption of saturated and trans fats, used in the formulation of lipid-based foods, is associated with incidence of health problems. Organogels or oleogels are a novel class of structured lipids formed from liquid oil as continuous phase entrapped within network of structuring molecules. The aim of this study was to understand the role of oils with different composition on the formation of glyceryl monostearate (GM) gel network. Glyceryl monostearate-based oleogels were produced with the minimal concentration of 5 wt% in sunflower (SF), high oleic sunflower oil (HOS) and coconut oil (CO). The influence of the oil type on the physicochemical properties of the gel was analyzed. The GM gels showed a solid-like behavior using either high oleic sunflower or sunflower oils but did not form a true gel with coconut oil. Although different oils could affect the crystal formation, all gels exhibited needle-like crystal morphology regardless solvent quality. The GM crystals arranged in a lamellar configuration are responsible for entrapping both SF and HOS oils. Degree of saturation of oils might affect GM oleogel properties. Long chain monounsaturated fatty acids favored the packing of GM crystals in a cohesive gel. Furthermore polymorphism with preferential crystalline β' form of GM was formed using a medium containing one and two unsaturation. In conclusion, it was observed that the type of oil influenced the formation of the GM gel network. These findings allow the better understanding of GM-based oleogels, providing opportunity to design for food products with improved technological and nutritional properties.

Whipped oil stabilised by surfactant crystals

We describe a protocol for preparing very stable air-in-oil foams starting with a one-phase oil solution of a fatty acid (myristic acid) in high oleic sunflower oil at high temperature. Upon cooling below the solubility limit, a two-phase mixture consisting of fatty acid crystals (length around 50 μm) dispersed in an oil solution at its solubility is formed which, after whipping, coat air bubbles in the foam. Foams which do not drain, coalesce or coarsen may be produced either by increasing the fatty acid concentration at fixed temperature or aerating the mixtures at different temperatures at constant concentration. We prove that molecular fatty acid is not surface-active as no foam is possible in the one-phase region. Once the two-phase region is reached, fatty acid crystals are shown to be surface-active enabling foam formation, and excess crystals serve to gel the continuous oil phase enhancing foam stability. A combination of rheology, X-ray diffraction and pulsed nuclear magnetic resonance is used to characterise the crystals and oil gels formed before aeration. The crystal-stabilised foams are temperature-sensitive, being rendered completely unstable on heating around the melting temperature of the crystals. The findings are extended to a range of vegetable oil foams stabilised by a combination of adsorbed crystals and gelling of the oil phase, which destabilise at different temperatures depending on the composition and type of fatty acid chains in the triglyceride molecules.

12-Hydroxystearic acid SAFiNs in aliphatic diols – a molecular oddity

12-Hydroxystearic acid (12-HSA), a structurally simple and cost-effective low molecular weight organogelator, has been studied extensively.

Preparation of organogel with tea polyphenols complex for enhancing the antioxidation properties of edible oil

Food-grade organogels are semisolid systems with immobilized liquid edible oil in a three-dimensional network of self-assembled gelators, and they are supposed to have a broad range of potential applications in food industries. In this work, an edible organogel with tea polyphenols was developed, which possesses a highly effective antioxidative function. To enhance the dispersibility of the tea polyphenols in the oil phase, a solid lipid-surfactant-tea polyphenols complex (organogel complex) was first prepared according to a novel method. Then, a food-grade organogel was prepared by mixing this organogel complex with fresh peanut oil. Compared with adding free tea polyphenols, the organogel complex could be more homogeneously distributed in the prepared organogel system, especially under heating condition. Furthermore, the organogel loading of tea polyphenols performed a 2.5-fold higher antioxidation compared with other chemically synthesized antioxidants (butylated hydroxytoluene and propyl gallate) by evaluating the peroxide value of the fresh peanut oil based organogel in accelerated oxidation conditions.

Effect of Storage Conditions on Apparent Viscosity of Oleogel Developed by β-Sitosterol and Lecithin with Sunflower Oil

The influence of storage conditions on apparent viscosity of mixtures of β-sitosterol and lecithin in sunflower oil was studied using rheology. The results showed the apparent viscosity of oleogel decreased with the increase of the speed of shear and storage temperature, while incresed with prolong of time in experiment conditions. The β-sitosterol and lecithin ratio also affected the apparent viscosity; solutions with ratio (70 β-sitosterol-30 lecithin) performed the highest apparent viscosity. What’s more, all the samples were pseudoplastic fluid. The apparent viscosity of the oleogel depends on storage temperature, storage time and organogelator ratios.

Rheological characterization of a new type of colloidal dispersion based on nanoparticles of gelled oil

The rheological properties of a new type of colloidal dispersion based on nanoparticles of gelled oil have been characterized. The nanoparticles (mean diameter approximately 250 nm) were viscoelastic droplets of dicaprylyl ether gelled by 12-hydroxystearic acid (HSA) and were stabilized in aqueous solutions by cetyltrimethylammonium bromide. The effects of the volume fraction of the dispersed organogel phase and of the organogelator concentration upon viscoelasticity of the dispersion were investigated and compared to the corresponding emulsion (without HSA). The shear viscosity of the dispersions of organogel droplets and the elastic and viscous moduli (G' and G'') were found to increase when the proportion of organogelator was increased. More surprisingly, the shear-thinning behavior was also more pronounced. The rheological behavior of the dispersions could be explained by strong interactions between some gelled particles. This hypothesis was supported by electron microscopy observations showing some particles bridged together by ribbons of HSA fibers.