Rare synonym for 蛋白質 (たんぱくしつ). Used mainly in older or specialized texts.
See also: タンパク質
In older literature, 卵白質 is sometimes used with the same meaning as 蛋白質 (protein).
Compound of 卵白 (egg white) and 質 (substance), referring to the protein found in egg whites. The exact historical derivation is uncertain; it is now largely replaced by 蛋白質.