2.2. Methods
Nitrogen and available lysine determinations were performed after dialysis to remove free amino acids commonly added to infant formulas. The defatted samples were dialyzed against distilled water through dialysis tubing, 12 000 MW, with constant stirring at 4°C for 72 h.
Total nitrogen was determined in duplicate by the Kjeldahl method using a digestor Büchi 430 and a N2 distillation unit Büchi 320 (Büchi Laboratoriums-Technik AG, Flawil, Switzerland).