蛋白 alone usually means egg white. For 'protein' the full word is 蛋白质 (dànbáizhì), though 蛋白 is used as shorthand in casual speech and compounds like 蛋白粉 (protein powder).
memory
Picture cracking an egg: the white (白) part of the egg (蛋) = 蛋白. From there, scientists named the molecule found in it 'protein' (蛋白质).
