Controlling oleogel crystallization using ultrasonic standing waves

Abstract

Oleogels are lipid-based soft materials composed of large fractions of oil (> 85%) developed as saturated and hydrogenated fat substitutes to reduce cardiovascular diseases caused by obesity. Promising oleogels are unstable during storage, and to improve their stability careful control of the crystalline network is necessary. However, this is unattainable with state-of-the-art technologies. We employ ultrasonic standing wave (USSW) fields to modify oleogel structure. During crystallization, the growing crystals move towards the US-SW nodal planes. Homogeneous, dense bands of microcrystals form independently of oleogelator type, concentration, and cooling rate. The thickness of these bands is proportional to the USSW wavelength. These new structures act as physical barriers in reducing the migration kinetics of a liposoluble colorant compared to statically crystallized oleogels. These results may extend beyond oleogels to potentially be used wherever careful control of the crystallization process and final structure of a system is needed, such as in the cosmetics, pharmaceutical, chemical, and food industries. Abbreviations USSW Ultrasonic standing wave HIU High-intensity ultrasound Oleogels are lipid-based materials that contain 85%-99.5% liquid oil trapped in a network of structuring molecules called oleogelators 1. Oleogels were developed during the last 15 years as saturated and hydrogenated fat substitutes 2. Saturated fats are used in the food, cosmetics, and pharmaceutical industries due to their ability to form solid and crystalline structures at room temperature. These crystalline structures are employed as delivery and protective systems and structuring agents 3. However, excessive consumption of saturated fats correlates with obesity that in turn causes cardiovascular diseases, metabolic syndrome and type-2 diabetes 4-6. Obesity is a global problem. In 2014, 2.5 billion adults and 41 million children worldwide were overweight or obese; these numbers have doubled since 1980 7. The annual healthcare costs related to treating diseases caused by/related to obesity is 60 billion euros in Europe 8 and 210 billion dollars in the USA 9. Lowering the intake of saturated fats, for example, by using oleogels rich in polyunsaturated fatty acids can help reduce cardiovascular diseases caused by obesity. Oleogels can be prepared using direct 1 and indirect 10 methods. Indirect methods are foam, emulsion and solvent exchange and aerogel templating where proteins or polysaccharides are used to prepare the scaffold in which oil is absorbed/retained 10. The direct method makes use of self-assembling molecules (e.g. monoglycerides, waxes, fatty acids, fatty alcohols, ethyl cellulose, phytosterols, phytosterol esters, etc.) to gel the oil 1. Structuring agents are dispersed into the oil, and then a heating and a cooling step are successively applied. The oleogelators rearrange themselves during the cooling step to form a crystalline/polymeric network. The network entraps the oil and gels the system 11. The direct method is...

Application of Analytical Methods for the Comprehensive Analysis of Oleogels—A Review

“…By implying GC, Moghtadaei [82] concluded that the cooling temperature or the concentration of the structuring agent, namely beeswax, did not influence the fatty acid profiles of the oleogel sample, which was abundant in linoleic acid. High-intensity ultrasound application on a high oleic sunflower oil structured with myverol monoglicerides did not statistically affected the main composition [31].…”

“…Using synchrotron light X-ray diffraction, microcrystals of monoglycerides were revealed in the structure of an oleogel developed under ultrasonic standing waves, while in oleogels which crystallized in statical conditions, the microcrystals were absent. The monoglycerides in the sample treated with ultrasounds of 1 MHz, exhibited the triclinic β-form, and a lamellar thickness of 48 Å-49 Å was observed, while for the rest of the samples the thermodynamically stable form was observed, namely the hexagonal α-form with a slightly bigger lamellar thickness dimension [31].…”

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

“…The viscosity was higher for 12HSA organogels than that of the CW ones, which corroborated the microscopy findings earlier described. A more densely packed crystal network, such as seen for 12HSA organogels, can reduce the mobility of the components inside the organogels by increasing the tortuosity of the system [ 29 ]. Crystals acted as barriers against the organogel flow during the viscosity analysis.…”

Automated image analysis method for oil-release test of lipid-based materials

“…Images were saved in a temporary folder of Windows and should be transferred to the destination folder after completion of analysis. A 10% monoglyceride-based oleogel was selected here as an example of LBM (more information about the oleogel preparation procedure can be found in [7] ). After preparation, the oleogel was cut into cylinders (diameter: 20 mm, height: 7-10 mm, mass: 3.25 ± 0.5 g) using a metallic cylindrical shaper with thin walls and was placed on a filter-paper disk (Whatman filter paper #2 disk, material: cellulose, pore size: 8 µm, thickness: 190 µm, diameter: 15 cm), which was then placed on the tripod.…”

“…The full sequence of images is presented in the supplementary material as a gif file (Oil Release GIF). Data were then fitted using a power law equation ( , where y is the total oil stain area, K is the rate constant, x is time, and n is the exponent; the procedure used is described in [7] ). The large number of data points coupled with the quality of the data yielded low-fitting errors on the estimated parameters ( Fig.…”