Determining the structure and stability of essential oil-sunflower wax and beeswax oleogels

In this study, essential oil oleogels were produced using eucalyptus, lavender, lemon peel and tea tree oils with sunflower and beeswax. The physicochemical, thermal, textural, and structural features of the oleogels were determined. For the essential oils used, an addition level of less than 15% of beeswax (BW) was insufficient to form stable oleogels, whereas an addition level of 10% of sunflower wax (SW) was sufficient to form stable oleogels. The acid and peroxide values of the gels were higher than those of the oils. All of the oleogels exhibited peaks around 3.70 and 4.10, indicating the presence of β' polymorphic forms. The hardness and stickiness values of the oleogels were influenced by the type and level of wax addition, as well as the viscosity of the oil used. Based on the thermal analysis results, the oleogels based on beeswax exhibited lower melting properties compared to those based on sunflower wax. The thermogravimetric data indicated that the polymeric matrices formed by the waxes, which depended on the type and level of wax addition, affected the vaporization of the volatiles. In conclusion, oleogels represent a green and sustainable approach for reducing the loss of volatile or bioactive compounds from various essential oils, which are widely used in the food, cosmetics, and pharmaceutical industries.     

Effect of Tween 20 on the Properties of Stearate Oleogels: an in-Depth Analysis

This work deals with the investigation of the polymorphic changes associated with stearic acid in the presence of Tween 20 during the formation of oleogels. Tween 20 was utilized as a crystal habit modifier and its effect on the physical and thermal properties of the oleogels have been studied. Tween 20 was found to stabilize the polymorph B of stearic acid, marked by an increase in the leaf‐like structures. Fluorescent recovery after photobleaching studies suggested Tween 20 concentration‐dependent reduction in the mobile fractions. Gelation studies suggested a delay in the induction time of nucleation of stearic acid in the presence of Tween 20 was due to the decrease in the degree of supercooling. Avrami analysis supported the stabilization of the polymorph B of stearic acid in the presence of Tween 20. XRD measurements indicated that Tween 20 promoted the growth of the stearic acid crystals while forming leaf‐like structures. The molecular rearrangement of the gelator network was quicker and ordered in the Tween 20‐containing oleogels. The increase in ordered arrangement of the stearic acid molecules has lowered the crystal imperfections. In other words, it enhanced the crystal gaps (pores) associated with the gelators. When stress (either thermal or mechanical) was introduced, the strength of the oleogels was decreased due to the syneresis of oil through the pores. An increase in the Tween 20 concentration‐dependent relaxation of the oleogels was also observed due to the polymorphic change and arrangement of the gelators.     

Tribological,rheological, and microstructural characterization of oleogels based on EVA copolymer and vegetables oils for lubricant applications

This work deals with the development of oleogels based on conventional (SO) and high-oleic sunflower (HOSO) vegetable oils and ethylene–vinyl acetate copolymer (EVA) for lubricant applications. Particularly, the influence of EVA concentration on the tribological, rheological properties and microstructure of these oleogels was analyzed. The results showed that the evolution of linear viscoelasticity functions was similar to that found for lithium greases. The different fatty acid profile in vegetable oils tested exerted an important influence on friction and wear in the ball-on-plates contact. The friction coefficient values became lower when EVA content was decreased. The wear marks obtained after the frictional tests for EVA–SO oleogels significantly reduced the wear scars versus EVA–HOSO oleogels and it was similar to commercial grease.     

Use of High-Intensity Ultrasound to Change the Physical Properties of Oleogels and Emulsion Gels

The objective of this work was to evaluate the effect of high-intensity ultrasound (HIU) on the physical properties of a soft oleogel (2% of candelilla wax, 2% of monoacylglycerol, and 2% of hardfat) and of water-in-oil (W/O) emulsion gels (EG) with various amounts of water (0%, 5%, and 25%). Physical properties of these systems such as thermoresistance, microstructure, melting profile, hardness, rheology, and oil loss were measured. When HIU was applied to the oleogel for 3 min using a 3.2 mm-diameter tip at an amplitude of vibration of 216 μm, a reduction in crystal size and crystal area (P < 0.05) was observed with an increase in hardness and no change in G′ nor in oil loss compared to the nonsonicated oleogel. Other sonication conditions (lower power levels, shorter durations, and bigger tips) tested in this study reduced the hardness and elasticity of the sample and increased oil loss. When HIU (3.2 mm-diameter tip, 216 μm, 3 min) was used in emulsions, harder and more elastic (P < 0.05) samples were obtained only in the samples with 25% water. This study shows that the texture of oleogels and EG with 25% of water can be improved by using HIU. The impact of these results is that the fat content of an EG can be reduced by 25% by adding water and HIU can be used to recover the structure lost due to water addition.     

Hansen Solubility Parameters as a Tool in the Quest for New Edible Oleogels

By identifying the Hansen space of nonfood‐grade gelators, which are capable of gelling oil, insights into the molecular characteristics required for gelation of edible oil become apparent. In examining the 34 reported oleogelators, molecules that gel oil tend to have a dispersive Hansen solubility parameter (HSP) between 16.0 < δ_d > 17.5 MPa^1/2, a polar HSP between 7.0 < δ_p > 11.0 MPa^1/2, and a hydrogen‐bonding HSP between 7.0 < δ_h > 9.0 MPa^1/2. Although this does not define the complete Hansen space of these gelators, it provides insight into what types of molecules may be capable of forming oleogels in vegetable oils to allow new discovery without relying solely on serendipity.     

Microstructuring process in oleogels formulated with vegetable oils and monoglycerides: A comparison of non-isothermal nucleation kinetics by spectrophotometric and DSC analysis

The initial oleogelation process (microstructuring) as well as the formulation are determinant to obtain the desired characteristics in oleogels with potential application in the industry. The microstructuring process in oleogels has been extensively studied by means of techniques highly sensitive to thermal variations, such as differential scanning calorimetry (DSC). However, there are other readily available techniques and equipment that can be employed to perform similar evaluations. Non-isothermal nucleation kinetics by spectrophotometric methods can be used as alternatives to basic crystallization studies in oleogels. Therefore, in this research a comparison of both techniques is presented, highlighting their similarities, advantages and limitations, in the study of the microstructure of oleogels. Oleogels were obtained with a minimum concentration of gelator and another saturated one, using vegetable oils of different degrees of saturation. The crystallization profiles of the oleogels were obtained by DSC, a non-isothermal nucleation kinetics was performed from the molten system and the final microstructure was evaluated by optical microscopy. The Fisher-Turnbull and Avrami model was used to evaluate the behavior during microstructuring. A gap was observed during the crystallization process by DSC which can be evaluated by spectrophotometry. Differences in the microstructuring process were found in both methods due to the temperature ramp used and formulation variables. The results obtained by spectrophotometry indicate that it can be a good alternative, easily accessible in oleogel crystallization studies, when high sensitivity or very specific thermal parameters are not required.