emulsifier

An emulsifier is a substance that stabilizes an emulsion, a mixture of two immiscible liquids, by reducing interfacial tension and by forming a protective layer around droplets. By lowering the surface tension, emulsifiers facilitate the dispersion of one liquid as droplets within another and help prevent coalescence. Emulsions can be oil-in-water or water-in-oil, depending on the relative affinities of the phases and the emulsifier's properties.

Emulsifiers can be synthetic surfactants or natural ingredients. Common food-grade emulsifiers include lecithin (phospholipids), mono- and diglycerides, and polysorbates. Natural emulsifiers include egg yolk, casein, gum arabic, and certain proteins and starches. Chemically, emulsifiers are often surfactants belonging to anionic, cationic, nonionic, or amphoteric classes. A useful guideline for selecting a stabilizer is the hydrophilic-lipophilic balance (HLB) value: high HLB favors oil-in-water emulsions, low HLB favors water-in-oil.

Applications span foods (mayonnaise, dressings, ice cream), cosmetics (creams, lotions), pharmaceuticals (drug suspensions, topical formulations), and industrial products (paints, lubricants). Mechanisms beyond simple surfactancy include Pickering stabilization by solid particles.

Stability considerations include droplet size, phase separation, creaming; emulsions are sensitive to pH, ionic strength, temperature, and interactions with electrolytes and other ingredients, which can alter stability. Safety and regulation vary by jurisdiction; many emulsifiers used in foods and cosmetics carry regulatory status such as GRAS or approved classifications.