S-(2-Carboxyethyl)-L-cysteine (S-Carboxyethylcysteine) is a non-protein (modified) sulfur amino acid. S-(2-Carboxyethyl)-L-cysteine is present in Acacia seed. S-(2-Carboxyethyl)-L-cysteine can affect the seed’s protein use in rats. S-(2-Carboxyethyl)-L-cysteine suppresses the methionine-induced growth rate, and has a negative effect on the plasma amino acid levels in rats.