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The enzyme lysozyme can be used as a preservative in cheese to prevent late gas blowing caused by Clostridia and provides an alternative to nitrate or the bacteriocin nisin. Lysozyme acts against Gram-positive bacteria by hydrolysing the peptidoglycan layer between the sugar derivatives N-acetylglucosamine and N-acetylmuramic acid. For the use as food additive, it is produced from hen egg white, which contains the highest natural amounts of this enzyme (about 3.5% of the total protein content). However, lysozyme entails allergy risks representing one of the egg allergens besides the major hen egg white proteins ovalbumin, ovotransferrin (conalbumin) and ovomucoid. Different investigations addressing possible allergic reactions to lysozyme-containing cheese by skin prick tests, radioallergosorbent tests and double-blind, placebo-controlled food challenges came to controversial conclusions. Some studies found correlations between the consumption of lysozyme-containing cheese and acute allergic reactions, whereas in a recently published work, egg allergic patients did not show allergy symptoms after the oral intake of cheese containing lysozyme. In summary, it cannot be excluded that sufferers from an egg allergy show adverse reactions to lysozyme used as preservative in cheese. Therefore, the declaration of lysozyme on the packaging of lysozyme-containing cheese is mandatory.