albumen

Albumen, from the Latin albus meaning white, is a term used in biology, botany, and photography to denote a viscous, protein-rich substance that surrounds or constitutes nourishing tissue.

In eggs, albumen is the white surrounding the yolk. It cushions and nourishes the developing embryo and makes up most of the egg’s mass. Fresh albumen is about 90 percent water and 10 percent proteins, with ovalbumin as the dominant protein, followed by ovotransferrin, ovomucoid, ovomucin, and lysozyme. It occurs as a thick inner layer and a thinner outer layer. The pH of fresh albumen is near neutral to slightly alkaline and increases as carbon dioxide escapes during storage, aging the white.

In botany, albumen denotes the endosperm, the nutritive tissue of seeds that surrounds the embryo. It can be rich in starch, oils, or proteins. Some seeds remain albuminous after maturation, while others are exalbuminous, having little or no endosperm left to feed the germinating embryo. Examples include maize, which retains prominent endosperm, and many legumes that lose it.

In photography, albumen printing was a prominent 19th-century process. Paper was coated with a thin layer of egg white (albumen) and salts, then sensitized with a silver nitrate solution. The albumen layer helped bind the light-sensitive compounds and produced a smooth, glossy surface with fine detail. The technique declined with the advent of gelatin-based papers and other processes in the late 19th and early 20th centuries.

Etymology traces to albus, white, reflecting the original association with the white of the egg.