Proteins soluble in water or dilute salt solutions and coagulable by heat — a classical solubility class occurring widely in foods, including conalbumin and ovalbumin in egg, lactalbumins in milk and leucosin in wheat. They foam, emulsify and gel, underpinning meringue structure, consommé clarification and bread crumb texture. Nutritionally they supply high-quality amino acids with good digestibility, and clinically, serum albumin levels serve as an indicator of protein status — linking food protein to medical nutrition. Heat coagulation, the property that firms an egg white, defines the class.