ABSTRACT
Hen egg white lysozyme is utilized as a food preservative with antimicrobial effects without any food toxicities. The bactericidal action of lysozyme is intensive on Gram-positive bacteria but much weaker on Gramnegative bacteria, because the former expose the cell wall consisting of peptidoglycan, while the latter has a unique cell envelope, which consists of the outer membrane, inner membrane, and peptidoglycan layer. Therefore, the perturbation of the outer membrane structure is needed to enhance the susceptibility to lysozyme of the peptidoglycan layer in Gram-negative bacteria. Despite this disadvantage, lysozyme is generally used as a food antiseptic. The antimicrobial action may be efficient on Gram-positive bacteria but ineffi-
cient on Gram-negative bacteria. Some attempts to enhance the antimicrobial action for Gram-negative bacteria have been done by our colleagues. Ibrahim et al. in 1991 found that the covalent attachment of palmitic acid residues to the lysyl residues of lysozyme
greatly enhanced the bactericidal action on E. coli (6). Nakamura et al. in 1991 reported that the Maillardtype lysozyme-polysaccharide conjugate also enhanced the bactericidal action on various Gram-negative bacteria (7). The antimicrobial action of lysozyme-dextran conjugate is shown in Figure 2. The bactericidal action is enhanced by heating at 50C. The polysaccharide attachment seems to stabilize lysozyme and to have stronger affinity to the outer membrane of Gram-negative bacteria. These modified lysozymes can be used as food antiseptics effective on various bacteria.
