Digestibility and peptide patterns of modified lysozyme after hydrolyzing by protease

In this study, lysozyme was modified by glucose in the dry state (50 degrees C, RH 75%) and the peptide patterns were investigated using HPLC after hydrolyzing by the pepsin-pancreatin system. Native or modified lysozyme was also administered to rats to clarify digestibility and absorbability in vivo. The digestibility of lysozyme modified by glucose decreased depending on reaction time. In vitro, when lysine residue of lysozyme was modified by glucose at a level of about 50%, the generated peptide patterns with molecular weights (MW) below 3,000 Da were similar to that of native lysozyme, and the yields of peptides from modified lysozyme were lower than those of native lysozyme. However, there are some differences between the hydrolysate patterns of native and modified lysozymes of MW over 10,000 Da, and the yields of these peptides from modified lysozyme are higher than those from native lysozyme. In vivo, the percentage of 30 d-modified lysozyme remaining in rat digestive tracts after 90 min of administration was 11% of the dosage as compared with 0.4% for native lysozyme. However, the digestive peptide patterns of native or modified lysozymes in the rat small intestine were also similar to those of the control. Consequently, it is estimated that modified lysozyme was digested as easily as native lysozyme when the degree of modification of lysine residue by glucose was about 60% even in vivo.