Enzymic Modification of Feather Keratin Hydrolysates with Lysine Aimed at Increasing the Biological Value

The lysine content of feather protein hydrolysate was modified via activation with alkaline proteinase and trypsin at pH 6·2 and 8·3, respectively. Lysine was used as the hydrochloride and the diacetyl derivative in the first case and as the methyl ester in the trypsin modification. The results indicate a lysine content of 26–35 g kg-1 and 59–64 g kg-1 after alkaline proteinase activation and 52–65 g kg-1 after trypsin activation. Considerable changes in the molecular mass profile of peptides were observed. Thus, enzyme modification is a way to raise the nutritive value of feather protein hydrolysate by increasing its lysine content (the main limiting essential amino acid).