Table 1.

Tryptophan content of proteins and foods (values in g/16 g N).^a,b

Analytical method	Lysozyme	Casein	Milk powder	Soy protein	Soy flour
Acid hydrolysis
Thioglycolic	5.84	1.27	nd	0.33	nd
Mercaptoethane-sulfonic	6.69	1.26	0.09	1.24	0.31
Methanesulfonic	5.72	0.71	nd	0.65	nd
p-toluenesulfonic	6.64	1.07	nd	1.01	nd
Basic hydrolysis
Sodium hydroxide	5.65	1.01	1.26	1.01	1.07
Barium hydroxide	—	1.30	1.25	1.81	0.81
Colorimetry
Acid ninhydrinc	7.66	1.70	1.73	1.36	1.91

^aValues are averages from 3 separate determinations except for a single assay by the acid ninhydrin procedure; nd, not detected.

^bNitrogen content (~): lysozyme, 16.2; casein, 13.6; milk powder, 5.32; soybean protein, 14.0; soybean flour, 8.32.

^cThe tryptophan content of lysozyme was calculated to be 7.66 g/16 g N from its known amino acid sequence and determined nitrogen content. Observed values were corrected for contributions of tyrosine to the absorbance at 385 nm by the following formula⁹: tryptophan (observed)/tryptophan expected = 1.013 + 0.034 (tyrosine/tryptophan).