Quantification of amino acid
Sericin powder was hydrolyzed with 6 M hydrochloric acid at 110 °C for 24 h under vacuum. Tryptophan was determined following alkaline hydrolysis. The hydrolysate was submitted to automated online derivatisation with o-phthalaldehyde and reversed phase high performance liquid chromatography (RP-HPLC) analysis in Agilent 1100 (Agilent Technology, Palo Alto, CA, UAS) assembly system using a Zorbax 80A C18column (4.6 i.d. × 180 mm), running at 0.5 ml/min. The results acquired were analyzed with the aid of ChemStation for LC 3 D software (Agilent Technology, Palo Alto, CA, USA).