Oleogels: How Sonication Improves Oleogel Formulations

Oleogels are versatile materials with applications in a wide range of industries, offering unique benefits in terms of texture, stability, and functionality. Using probe-type sonicators significantly improves the synthesis and performance of oleogels, making them more suitable for various industrial applications.

What are Oleogels?

Oleogels are semi-solid systems composed of an oil phase immobilized within a three-dimensional network of structuring agents, such as oleogelators or gelling agents. These structuring agents help to create a gel-like consistency in oils, resulting in a stable, spreadable, and often transparent or translucent product. Oleogels find applications across various industries, including food, cosmetics, pharmaceuticals, and industrial lubricants, offering benefits such as texture improvement in food products, moisturization in skincare items, controlled drug delivery in pharmaceuticals, and enhanced lubrication properties in industrial and cosmetic formulations.
When oleogels are produced using powerful ultrasound waves, a process known as sonication, the synthesis of these oil-based gels is improved. Read below how the effects of sonication facilitate the formation of oleogels!

Ultrasonic homogneization facilitates and improves the formulation of oleogels.

Ultrasonic Mixing of Oleogels

Ultrasonication can improve the synthesis of oleogels by enhancing the dispersion and distribution of the structuring agents within the oil phase. When high-intensity ultrasound waves are applied to the oil mixture containing the oleogelators, they promote uniform mixing and dispersion of the structuring agents, leading to a more homogeneous gel network. Additionally, sonication can facilitate the formation of smaller and more uniform particles, resulting in finer texture and improved stability of the oleogel. The cavitation effects generated by ultrasound can disrupt larger aggregates and promote the formation of smaller, more evenly dispersed structures within the gel matrix.

Ultrasonic Direct Dispersion for Oleogel Synthesis

Dispersion-Templated Oleogel: For the direct dispersion method, sonication is used to disperse the oleogelator directly into the liquid oil at temperatures surpassing its melting point, succeeded by a cooling phase where the gelator network solidifies, encapsulating the oil within a solid framework, thus yielding the oleogel. Employing this direct ultrasonic dispersing approach, the gelation process can generate two distinct network architectures, contingent upon the nature of the structurant utilized: crystallite conformations or self-assembled networks.

Ultrasonic Emulsion for Oleogel Synthesis

Emulsion-Templated Oleogel: Ultrasonic emulsion using probe-type sonication offers several advantages for oleogel synthesis, primarily by providing efficient and consistent mixing at micron- and nano-level. High-intensity ultrasonic waves create intense sonomechanical shear forces and acoustic cavitation, which break down the oil and gelator in the aqueous phase into uniformly sized droplets. This leads to a more stable and homogenous emulsion, which is important for the formation of oleogels with desirable texture and structural properties. Additionally, the localized heating effect of sonication can enhance the dissolution and interaction of gelators within the oil phase, improving the gelation process. Consequently, ultrasonic emulsion facilitates the production of oleogels with superior stability, consistency, and performance in various applications, including food, pharmaceuticals, and cosmetics.

Ultrasonic Homogenization of Water-In-Oleogel-In-Water Emulsions

Water-In-Oleogel-In-Water (W/O/W) emulsions offer exceptional functionalities that makes them ideal for food applications. For instance, Water-In-Oleogel-In-Water emulsions have been found to be a great carrier for delivering probiotics and safeguarding food aromas. Ultrasonic emulsification efficiently blends aqueous and oily phases into double emulsions, i.e. W/O/W emulsions. Incorporating aqueous droplets within the oil globules of fatty products decreases their fat content. Gelation of the oil phase in W/O/W emulsions imparts structural integrity and mitigates destabilization events like water droplet coalescence within the oil phase.
Sonication can aid in the formulation of Water-In-Oleogel-In-Water (W/O/W) emulsions by facilitating the dispersion and homogenization of the emulsion components. High-intensity, low-frequency sonication (at frequencies of approx. 20-26kHz) can break down larger droplets into smaller, more uniform droplets, promoting the formation of stable emulsions. Additionally, sonication can enhance the incorporation of aqueous droplets into the oil phase and improve the dispersion of the oleogelator within the oil phase, leading to more efficient gelation and enhanced stability of the emulsion. Furthermore, sonication can help to control the size distribution of the emulsion droplets, resulting in emulsions with desirable properties such as improved texture, mouthfeel, and sensory attributes.

Scheme representing of different types of oleogel-based emulsion systems.
Study and image: ©Pinto et al., 2021

Scientifically Proven: The Effectiveness of Ultrasonic Dispersion of Oleogels

Noonim et al. (2022) investigated the effect of sonication using the Hielscher sonicator UP200St on physical, thermal, and structural properties and storage stability of palm oil-based oleogels prepared using different concentrations of carnauba wax (5% or 10%) were investigated and compared with oleogels prepared with a homogenizer (2000 rpm for 10 min). Sonication allowed to prepare oleogels with higher carnauba wax concentration (10%) and effectively improved the properties and stability of palm oil-based oleogel (p < 0.05).

Oleogel for Food Applications

Protocol for an Oleogel produced for a Vegan Mayonnaise
 
Vegan Culinary Cream based on Oleogel
(cf. Szymanska et al., 2024)
 
Ingredients:

• rapeseed oil
• palm oil
• linseed oil
• candelilla wax
• soy drink

The oleogels (100 g) were prepared as follows: Firstly, 3–7% candelilla wax (w/w) was dispersed in a mixture of refined rapeseed and linseed oils (1:1 w/w) by heating for 10 min at 80 ± 1 °C in a water bath and then sonication for 10 s (26 kHz, 72 W, 100% pulse, 100% amplitude) using the ultrasound homogenizer UP200St (Hielscher Ultrasonics), equipped with the titanium sonotrode S26d7. The clear, homogeneous mixture was statically cooled in a thermostatic cabinet for 24 h at 20 ± 1 °C, until the proper structure was formed. The oleogels were obtained in three repetitions.
If you are interested in the ultrasonic emulsification of mayonnaise, you will find recipe, video and detailed information here!

Preparation of Cream-Type Emulsions using the Ultrasonic Oleogel

Cream-type O/W (30/70 w/w) emulsions (100 g) were prepared according to the procedure in our preliminary research [38] with slight modifications. Both an aqueous phase (soybean drink containing 2.6% w/w protein) and a lipid phase (palm oil or oleogel) were preheated up to 55 °C and immediately homogenized by using the ultrasound homogenizer UP200St (Hielscher Ultrasonics) with a frequency of 26 kHz. The following parameters were used: 100% pulse, 80% amplitude, 15 mm immersion of the sonotrode in the central part of the beaker (200 mL capacity). The homogenization time of 2.5 min (τ) was determined on the basis of the results of technological tests and preliminary tests, taking into account the increasing temperature of the samples (for τ = 2.5 min: energy density: 69.1 ± 0.4 J∙g–1, max. temperature: 61.0 ± 0.3 °C). Sodium benzoate of 0.15% (w/w) was added to the aqueous phase as an antibacterial agent.

Most commonly used oleogelators for food-grade oleogels.
Scheme: ©Perta-Crisan et al., 2023.