In the method alkaline hydrolysis of proteins was used due to the destruction of tryptophan structure
during acid hydrolysis. Following alkaline hydrolysis (120 C for 12 h), hydrolysates are filtered through
ashless filter paper and pH values are adjusted with hydrochloric acid solution. Separation and detection
of tryptophan are performed on a reversed-phase column with fluorescence detection within 10 min by
using a mobile phase of acetonitrile and acetate buffer of pH 6.3 (1:9, v/v).