Self-assembled trehalose amphiphiles as molecular gels: A unique formulation to wax-free cosmetics

Trehalose has been used as an emollient and antioxidant in cosmetics. We aimed to explore trehalose amphiphiles as oil structuring agents for the preparation of gel-based lip balms as part of wax-free cosmetics. This article describes the synthesis of trehalose fatty acyl amphiphiles and their corresponding oleogel-based lip balms. Trehalose dialkanoates were synthesized by esterifying the two primary hydroxyls of trehalose with fatty acids (C4-C12) using a facile, regioselective lipase catalysis. The gelation potential of as-synthesized amphiphiles was evaluated in organic solvents and vegetable oils. Stable oleogels were subjected to X-ray diffraction (XRD), thermal (DSC), and rheological studies and further used for the preparation of lip balms. Trehalose dioctanoate (Tr8), trehalose didecanoate (Tr10) were found to be super gelators as their minimum gelation concentration is ≤0.2 wt%. XRD studies revealed their hexagonal columnar molecular packing while forming the fibrillar networks. Rheometry proved that the fatty acyl chain length of amphiphiles can influence the strength and flow properties of oleogels. Further rheometry (at 25, 37, and 50 °C) and DSC studies have validated that Tr8- and Tr10-based oleogels are stable for commercial applications. Tr8- and Tr10-based olive oil oleogels were used for the preparation of lip balms. The preliminary results suggested that the cumulative effect of trehalose's emolliency and vegetable oil gelling nature can be achieved with trehalose amphiphiles, specifically, Tr8 and Tr10. This study has also demonstrated that Tr8- and Tr10-based lip balms can be used as an alternative to beeswax and plant wax lip balms, indicating their huge potential to succeed as a new paradigm to formulate wax-free cosmetics.     

Physical Properties of Beeswax,Sunflower Wax,and Candelilla Wax Mixtures and Oleogels

To be able to tailor and optimize the physical properties of oleogels for various food applications, more information is needed to understand how different gelators interact. Therefore, the objectives of this study were to evaluate the interactions between binary mixtures of beeswax (BW), candelilla wax (CLW), and sunflower wax (SFW) in pure form as well as in 5% wax oleogels made with soybean oil, in terms of their crystallization and melting properties, crystal morphology, solid fat content, and gel firmness. CLW:BW mixtures had eutectic melting properties, and oleogels from these mixtures with 40:60 to 90:10 CLW:BW were firmer compared to oleogels made with one wax. The main components in SFW and BW appeared to cocrystallize or crystallize at the same temperature, but nonlinear changes in melting point and solid fat content profile of oleogels prepared with the mixed waxes indicated that SFW dominated oleogel formation. In addition, oleogels prepared with mixtures of SFW and BW had lower firmness compared to oleogels prepared with one wax, indicating an incompatibility between the two waxes. The main wax components in SFW and CLW never cocrystallized, and low levels of CLW appeared to prevent SFW from forming a crystalline platelet network. This resulted in low firmness of oleogels made from mixtures of 90:10 to 60:40 SFW:CLW compared to oleogels prepared with one wax. However, the firmest oleogels of all mixtures were made from 10:90 SFW:CLW. Changes in gel firmness and melting properties with mixed wax oleogels were likely to be due to changes observed in the crystal size and morphology. In addition, the firmest gels were shown to result from mixtures that were predicted to have >40% hydrocarbon content, and a high hydrocarbon to wax ester ratio, but minor components such as free fatty acids and fatty alcohols may have also influenced firmness.     

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.     

Effect of oil unsaturation and wax composition on stability,properties and food applicability of oleogels

Oleogelation is emerging as one of the most exigent oil structuring technique. The main objective of this study was to formulate and characterize rice bran/sunflower wax-based oleogels using eight refined food grade oils such as sunflower oil, mustard oil, soybean oil, sesame oil, groundnut oil, rice bran oil, palm oil, and coconut oil. Stability and properties of these oleogels with respect to oil unsaturation and wax composition were explored. Sunflower wax exhibited excellent gelation ability even at 1%–1.5% (w/v) concentration compared to rice bran wax (8%–10% w/v). As the oleogelator concentration increased, peak melting temperature also increased with increase in strength of oleogels as per rheological studies. X-ray diffraction and morphological studies revealed that oleogel microstructure has major influence of wax composition only. Sunflower wax oleogels unveiled rapid crystal formation with maximum oil binding capacity of 99.46% in highly unsaturated sunflower oil with maximum polyunsaturated fatty acid content. Further, the applicability of this wax based oleogels as solid fat substitute in marketed butter products was also scrutinized. The lowest value of solid fat content (SFC) in oleogel was 0.20% at 25°C, resembling closely with the marketed butter products. With increase in oil unsaturation, oleogels displayed remarkable reduction in SFC. Depending upon prerequisite, oleogel properties can be modulated by tuning wax type and oil unsaturation. In conclusion, this wax-based oleogel can be used as solid fat substitute in food products with extensive applications in other fields too.     

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.     

Physical Properties of Soybean Oleogels and Oil Migration Evaluation in Model Praline System

The present study examined the physical properties of soybean oleogels and commercial confectionery filling fats and evaluated the oil migration properties in model praline systems. Soybean oleogels were prepared using different oleogelators namely monoglyceride (MAG oleogels) and a mixture of sorbitan tri‐stearate (STS) with lecithin (50:50) (Lec‐STS oleogels). Both MAG oleogels and Lec‐STS oleogels demonstrated a flat solid fat content (SFC) profile with zero SFC at 40 °C. At low temperature, MAG oleogels and Lec‐STS oleogels demonstrated a non‐flowing gel‐like property due to the ability of the oleogelator to entrap liquid oil. In addition, oleogels also showed thixotropic behavior indicating the possible capability to prevent migration of filling fats to coatings and also good flow ability during pumping though manufacturing equipment. The textural property of oleogels also did not change significantly upon storage indicating good structural stability. When used as in a model praline system, oleogels demonstrated a migration delaying property.     

Supramolecular Phase-Selective Gelation by Peptides Bearing Side-Chain Azobenzenes: Effect of Ultrasound and Potential for Dye Removal and Oil Spill Remediation

Phase selective gelation (PSG) of organic phases from their non-miscible mixtures with water was achieved using tetrapeptides bearing a side-chain azobenzene moiety. The presence of the chromophore allowed PSG at the same concentration as the minimum gelation concentration (MGC) necessary to obtain the gels in pure organic phases. Remarkably, the presence of the water phase during PSG did not impact the thermal, mechanical, and morphological properties of the corresponding organogels. In the case of miscible oil/water mixtures, the entire mixture was gelled, resulting in the formation of quasi-hydrogels. Importantly, PSG could be triggered at room temperature by ultrasound treatment of the mixture or by adding ultrasound-aided concentrated solution of the peptide in an oil-phase to a mixture of the same oil and water. Moreover, the PSG was not affected by the presence of salts or impurities existing in water from natural sources. The process could be scaled-up, and the oil phases (e.g., aromatic solvents, gasoline, diesel fuel) recovered almost quantitatively after a simple distillation process, which also allowed the recovery and reuse of the gelator. Finally, these peptidic gelators could be used to quantitatively remove toxic dyes from aqueous solutions.     

Oleogels Based on Palmitic Acid and Safflower Oil: Novel Formulations for Ocular Drug Delivery of Voriconazole

The gelation of the vegetable oils using fat crystals has gained significant attention in recent years. These formulations have been explored for food and pharmaceutical applications. The alteration in the properties of palmitic acid (20–40% w/w) and safflower oil oleogels is extensively studied at microscopic and macroscopic levels. The thermal and mechanical stability of the oleogels is improved when the proportion of the palmitic acid content is increased. However, under stress, the fat crystal network junction zones of the oleogels with higher proportions of palmitic acid undergo disruption. The changes in the properties of the oleogels are due to the alteration in the molecular packing, crystallite size, and lattice strain of the fat crystal network. The alteration in the properties is governed by the changes in the extent of inter‐ and intramolecular hydrogen bonding within the components of the oleogels. The oleogels can demonstrate the ability to deliver the drug, voriconazole, across the corneal tissue. Further, the prepared oleogels are biocompatible to murine fibroblast cells and do not elicit adverse reactions when instilled within the ocular sac of rabbits. The results suggest that the oleogels can be tried as ocular delivery vehicles. Practical Applications: The delivery of drug into the internal structure of the eye is a great challenge for the ophthalmologists. Usually no more than 1% of the drug can be delivered through conventional techniques. Various researchers have proposed the use of lipid‐based ocular drug delivery systems. Some of them include solid liquid nanoparticles, emulsions, and liposomes. However, the preparation of these formulations requires a tedious process. Keeping this in mind, it is proposed to synthesize oleogel as probable ocular drug delivery system.     

Properties of Oleogels Formed With High‐Stearic Soybean Oils and Sunflower Wax

In an effort to develop alternatives for harmful trans fats produced by partial hydrogenation of vegetable oils, oleogels of high‐stearic soybean (A6 and MM106) oils were prepared with sunflower wax (SW) as the oleogelator. Oleogels of high‐stearic oils did not have greater firmness when compared to regular soybean oil (SBO) at room temperature. However, the firmness of high‐stearic oil oleogels at 4 °C sharply increased due to the high content of stearic acid. High‐stearic acid SBO had more polar compounds than the regular SBO. Polar compounds in oil inversely affected the firmness of oleogels. Differential scanning calorimetry showed that wax crystals facilitated nucleation of solid fats of high‐stearic oils during cooling. Polar compounds did not affect the melting and crystallization behavior of wax. Solid fat content (SFC) showed that polar compounds in oil and wax interfered with crystallization of solid fats. Linear viscoelastic properties of 7% SW oleogels of three oils reflected well the SFC values while they did not correlate well with the firmness of oleogels. Phase‐contrast microscopy showed that the wax crystal morphology was slightly influenced by solid fats in the high‐steric SBO, A6.     

Increasing the firmness of wax-based oleogels using ternary mixtures of sunflower wax with beeswax:candelilla wax combinations

Oleogels were prepared with 5% wax in soybean oil using mixtures of beeswax (BW) and candelilla wax (CLW) with ratios of 10:90, 30:70, 50:50, and 60:40 BW:CLW, and the same series where 10% of the total wax was substituted with sunflower wax (SFW). The hypothesis that SFW would increase the firmness of the oleogels without affecting the melting properties was tested. Firmness of one-wax oleogels decreased from SFW > CLW > BW. Oleogels with 50:50 BW:CLW and 60:40 BLW:CLW had equal firmness to pure 5% SFW oleogels. SFW significantly increased oleogel firmness and reduced the softening that occurred between 4°C and 22°C. Increased firmness was also found with rice bran wax and behenyl-behenate (C44) addition, but not with wax esters with chain lengths ranging from 30 to 40 carbons (C30 to C40). By differential scanning calorimetry, SFW significantly decreased the melting point of oleogels with 10:90 and 30:70 BW:CLW mixtures but significantly increased the melting point of those with 50:50 and 60:40 BW:CLW mixtures. However, the solid fat content melting curves were not significantly influenced by SFW addition. These results indicate that mixed wax oleogels had greater hardness and elasticity, and that the long chain wax esters contributed by SFW helped to improve the strength of oleogels without negatively affecting their melting properties.     

Erythritol‐Based Medium‐Chain Sugar Amphiphile: Synthesis and Gelling Capability in Edible Oils

The production of organogels from vegetable oils requires low‐molecular‐weight gelators. Herein, a novel small‐molecule sugar ester gelator is synthesized from erythritol and octanoic acid. The purified reaction product is identified as erythritol 1,6‐dioctanoate by high performance liquid chromatography (HPLC) with evaporative light‐scattering detection and nuclear magnetic resonance (NMR). This low‐molecular‐weight erythritol ester exhibits self‐assembly behavior in vegetable oils with a minimum gelation concentration of 4 wt%. Microscopy reveals needle‐like crystals that became slender as the gelator concentration increases. X‐Ray Diffraction (XRD) analyses indicate that the organogels are semicrystalline with both crystalline and amorphous domains. Fourier Transform Infrared (FTIR) spectroscopy reveals that the gel structure is maintained by non‐hydrogen‐bonding interactions. Furthermore, rheological tests show that the mechanical strength of the gel is poor, but as the gelator concentration is increased, the mechanical strength and hardness of the gel also increases. Thus, this erythritol ester effectively promotes the gelation of edible vegetable oils and increases the variety of available organogelators. Practical Applications: The synthesized erythritol ester is successfully applied as a gelator to produce organogels from a variety of vegetable oils, and are expected to advance the development of effective organogelators for edible oils.     

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.     

烯丙基山梨醇凝胶因子的合成及凝胶性能研究

1, 3∶2, 4-二(对甲基苄叉)-D-山梨醇(MDBS)是一种凝胶能力突出的山梨醇缩醛类凝胶因子,对比MDBS本设计合成一系列烯丙基山梨醇缩醛,并通过凝胶因子之间的作用力、分子的几何构型及亲疏水作用等方面研究了凝胶因子在溶剂中的自组装及凝胶机理。考察了4种凝胶因子对30种常见有机溶剂的凝胶能力,以及凝胶因子在不同溶剂中的最低凝胶浓度。结果表明,凝胶因子的凝胶能力依赖于凝胶因子的分子结构,烯丙基的引入显著提高了凝胶因子的凝胶能力。研究了凝胶的形成机理,通过紫外光谱研究自组装力,通过场发射扫描电镜可以观察到凝胶呈纤维状和三维网状结构。     

The Effect of Addition of High-Melting Monoacylglycerol and Candelilla Wax on Pea and Faba Bean Protein Foam-Templated Oleogelation

Use of oleogels prepared from hydrocolloids has recently gained considerable attention as an alternative for trans and saturated fats. Lately, pulse proteins such as faba bean protein and pea protein have been successfully used to prepare oleogels using a foam-templated approach. Although the pulse proteins are healthy oleogelators, high oil loss and low quality of cake baked using pulse protein-stabilized oleogels due to its poor rheological properties challenged its use. The present study explored whether the addition of small amount of high-melting monoglyceride (MAG) or candelilla wax (CW) can be used to improve the oil binding capacity, rheological properties, and baking qualities of pulse protein-stabilized oleogels composed of 5% faba bean or pea protein concentrate with 0.25% xanthan gum foams. Different concentrations (0.5–3%) of MAG or CW were dissolved in canola oil at 80 °C, followed by addition into the freeze-dried protein-polysaccharide foams (pH 7) and quickly transferred to a refrigerator to facilitate the formation of oleogels. The crystallized additives were found to be reinforcing the protein foam network in the oleogels. With increase in concentration of CW and MAG, the oil binding capacity, firmness, cohesiveness, and storage moduli of the oleogels were increased. Oleogels with and without MAG or CW were then characterized and tested for their performance as a shortening replacer in model baked cakes. Findings showed improved textural properties of cake upon addition of MAG in the foam-templated oleogels, however, compared to the shortening, negative effect on cake hardness and chewiness was still observed with the oleogels.     

含吡啶小分子胶凝剂研究进展

简述了含吡啶结构的小分子胶凝剂的研究进展，介绍了这类胶凝剂的结构特点、胶凝行为和凝胶性能。     

Self-assembly of organogels via new luminol imide derivatives: diverse nanostructures and substituent chain effect

Luminol is considered as an efficient sycpstem in electrochemiluminescence (ECL) measurements for the detection of hydrogen peroxide. In this paper, new luminol imide derivatives with different alkyl substituent chains were designed and synthesized. Their gelation behaviors in 26 solvents were tested as novel low molecular mass organic gelators. It was shown that the length and number of alkyl substituent chains linked to a benzene ring in gelators played a crucial role in the gelation behavior of all compounds in various organic solvents. Longer alkyl chains in molecular skeletons in present gelators are favorable for the gelation of organic solvents. Scanning electron microscope and atomic force microscope observations revealed that the gelator molecules self-assemble into different micro/nanoscale aggregates from a dot, flower, belt, rod, and lamella to wrinkle with change of solvents. Spectral studies indicated that there existed different H-bond formations and hydrophobic forces, depending on the alkyl substituent chains in molecular skeletons. The present work may give some insight to the design and characteristic of new versatile soft materials and potential ECL biosensors with special molecular structures.     

Rice bran wax structured oleogels and in vitro bioaccessibility of curcumin

Curcumin, the bioactive compound found in turmeric, exhibits a wide range of health-promoting properties. However, its application in food formulations and as nutritional supplements is limited by its poor bioaccessibility. This study investigates the effects of curcumin on the structure formation and physical properties of oleogels made with three different concentrations of rice bran wax (RBW) (2%, 6%, and 10% w/w) compared to an ungelled control oil and examines the bioaccessibility of curcumin contained in those lipid systems. The physical and structural properties were characterized using a penetration test, solid fat content, polarized light microscopy, differential scanning calorimetry, and X-ray diffraction (XRD). Data analysis revealed no significant differences in polymorphic or thermal properties between oleogels with and without curcumin; however, differences in microstructural properties were documented for oleogels with curcumin. Moreover, the percent of lipid crystallinity in 6% and 10% RBW oleogel increased in samples containing curcumin. An in vitro simulated digestion study showed that curcumin bioaccessibility significantly increased with increasing RBW content relative to the ungelled control. Results from this study provide insight into the potential utilization of RBW oleogels for delivering curcumin and other poorly water-soluble compounds in food, dietary supplement, pharmaceutical, and cosmetic products.     

Mechanism of solvent entrapment within the network scaffolding in organogels: thermodynamic and kinetic investigations

A detailed investigation on the thermodynamic behaviour of the physical and chemical organogels, using differential scanning calorimetry (DSC) and modulated thermogravimetric analysis (MTGA), is presented. Aluminium soap of fatty acid was used as the physical gelator and in situ crosslinking of siloxane copolymer was used for chemical gelation. The effects of the type and concentration of the gelators and the corresponding mesh‐size distribution of the gel network scaffolding on the trapped‐solvent crystallization, melting and evaporation mechanism, and kinetics are examined. It appears that the kinetics of crystallization of the trapped‐solvent are significantly affected by the quality of the gel network scaffolding and can be treated successfully by the Avrami equation of crystallization. From the melting behaviour of the entrapped‐solvent crystallites, quantitative information about the number of solvent molecules bound per molecule of the gelator has been extracted. The effect of gelation network structure on the kinetics of evaporation of the solvent from the gel network scaffolding has been evaluated. DSC appears to be the reliable technique to evaluate the population distribution of solvent molecules trapped in the gel network scaffolding. Copyright © 2003 Society of Chemical Industry     

Regulation of substituent groups on morphologies and self-assembly of organogels based on some azobenzene imide derivatives

In this paper, new azobenzene imide derivatives with different substituent groups were designed and synthesized. Their gelation behaviors in 21 solvents were tested as novel low-molecular-mass organic gelators. It was shown that the alkyl substituent chains and headgroups of azobenzene residues in gelators played a crucial role in the gelation behavior of all compounds in various organic solvents. More alkyl chains in molecular skeletons in present gelators are favorable for the gelation of organic solvents. Scanning electron microscopy and atomic force microscopy observations revealed that the gelator molecules self-assemble into different aggregates, from wrinkle, lamella, and belt to fiber with the change of solvents. Spectral studies indicated that there existed different H-bond formations between amide groups and conformations of methyl chains. The present work may give some insight to the design and character of new organogelators and soft materials with special molecular structures.     

Production,health implications and applications of oleogels as fat replacer in food system: A review

Various food formulations widely utilized solid fats to provide specific textural properties and sensory attributes. Partially hydrogenated oil was commonly used as solid fat before being banned by FDA recently because of the existence of trans fats. Oleogels, semi-solid gel typically prepared from liquid vegetable oil and food-grade oleogelators, is developed as an alternative for solid fats that is free of trans fat and low in saturated fats. Oleogels are prepared via indirect or direct oleogelation technology by which the liquid oil is entrapped in a three-dimensional network with the aid of low molecular weight oleogelators (LMOGs) and high molecular weight oleogelators (HMOGs). Oleogels received tremendous attention from food scientists to be used in various food applications, particularly high-fat products such as comminuted meat, chocolates, ice cream, shortening and margarine and even as a deep-frying medium. They satisfy not only the current trends of consumers for healthy food products (free of trans fat and low in saturated fat) but also provide viscoelastic solid- and gel- like properties to structure high fat food products. More importantly, recent studies showed that oleogels tend to be metabolized differently from conventional fats and oils giving them an additional advantage in improving the nutritional value of high-fat foods. Therefore, this review aims to provide an overview that captures the latest studies on oleogels from their production via direct dispersion and indirect dispersion methods, processing conditions that influence the physical properties, metabolism and health attributes as well as recent application in food products.