Microemulsions are thermodynamically stable, isotropic mixtures of oil, water, and surfactants, often with a co-surfactant. They are typically in the size range of 10–100 nm, making them transparent or slightly opalescent. Unlike regular emulsions, which are kinetically stable but thermodynamically unstable, microemulsions form spontaneously when the components are mixed in the right proportions.
There are three primary types:
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Oil-in-water (O/W): Oil droplets dispersed in a continuous water phase.
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Water-in-oil (W/O): Water droplets dispersed in oil.
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Bicontinuous: Both oil and water form continuous domains, stabilized by a surfactant film.
Their unique characteristics include:
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High surface area
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Solubilization of both hydrophilic and lipophilic compounds
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Enhanced bioavailability for poorly soluble drugs
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Controlled release potential
Gut Taste Receptors
The gut contains taste receptors similar to those in the oral cavity, primarily located on enteroendocrine cells lining the gastrointestinal (GI) tract. These receptors can detect:
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Sweet (T1R2/T1R3)
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Umami (T1R1/T1R3)
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Bitter (T2Rs)
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Fat (CD36, GPR120)
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Other nutrient sensors like amino acid, salt, and microbial metabolites
Gut taste receptors are involved in:
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Nutrient sensing
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Hormone release (e.g., GLP-1, PYY, ghrelin)
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Satiety signaling
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Glucose homeostasis
Interaction Between Microemulsions and Gut Taste Receptors
Microemulsions may influence gut taste receptor activity in several ways:
1. Enhanced Delivery of Ligands
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Microemulsions can increase the solubility and stability of taste receptor ligands (like fatty acids, sweeteners, or bitter compounds).
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This may lead to more potent or prolonged receptor activation, affecting hormone release or satiety.
2. Targeted Release
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They can be designed to release contents at specific pH ranges (e.g., in the small intestine), optimizing interaction with localized receptors.
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Coatings or encapsulation can modulate the timing and location of ligand presentation.
3. Modulation of Receptor Sensitivity
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Certain surfactants or lipid components in microemulsions may interact with membranes, potentially altering receptor conformation or membrane microdomain organization.
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This could affect the sensitivity or signal transduction of taste receptors.
4. Synergistic or Antagonistic Interactions
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Microemulsions might co-deliver multiple compounds that either synergize or compete for the same receptors.
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E.g., fatty acids with GPR120 or bitter compounds with T2Rs.
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5. Influence on Microbiota
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Gut microbes also interact with taste receptors indirectly (e.g., via SCFAs).
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Microemulsions could alter microbiota composition or metabolic output, thereby influencing gut chemosensory pathways.
Applications and Implications
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Functional Foods: Enhancing nutrient sensing or satiety signals for appetite control.
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Pharmaceuticals: Targeting gut hormone release (like GLP-1) for metabolic diseases.
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Nutraceuticals: Improving bioavailability and activity of plant-derived bitter compounds or polyphenols.
References
Amiri-Rigi, A., Abbasi, S., & Emmambux, M. N. (2023). Background, limitations, and future perspectives in food grade microemulsions and nanoemulsions. Food Reviews International, 39(8), pp. 5048-5086.
Bellocq, A. M., Biais, J., Bothorel, P., Clin, B., Fourche, G., Lalanne, P., … & Roux, D. (1984). Microemulsions. Advances in Colloid and Interface Science, 20(3-4), pp. 167-272.
Flanagan, J., & Singh, H. (2006). Microemulsions: a potential delivery system for bioactives in food. Critical Reviews in Food Science and Nutrition, 46(3), pp. 221-237.
Paul, B. K., & Moulik, S. P. (1997). Microemulsions: an overview. Journal of Dispersion science and Technology, 18(4), pp. 301-367.
Rao, J., & McClements, D. J. (2011). Food-grade microemulsions, nanoemulsions and emulsions: Fabrication from sucrose monopalmitate & lemon oil. Food Hydrocolloids, 25(6), pp. 1413-1423.
Tenjarla, S. (1999). Microemulsions: an overview and pharmaceutical applications. Critical Reviews™ in Therapeutic Drug Carrier Systems, 16(5).
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