After precolumn
derivatizing with phthalic dicarboxaldehyde (OPA), the
filtrate was subjected to a reversed-phase high performance liquid
chromatography SYKAM Amino Acid Analyzer S 433D (Sykam
GmbH; Kleinostheim, Germany) with PEEK column (4.6 150 mm,
7 mm,10% crosslink) to determine the free amino acid compositions