Natural antimicrobials as additives and ingredients for the preservation of foods and beverages - Natural Food Additives, Ingredients and Flavourings - page 140

The activity of lysozyme against several food-borne pathogens and spoilage
bacteria has been demonstrated in vitro in laboratory media for L. monocytogenes,
C. botulinum, T. thermosaccharolyicum, G. stearothermophilus and S. aureus
(Hughey and Johnson 1987; Osa et al. 1990; Johansen et al. 1994; Pellegrini et al.
1997). However, the anti-listerial and anti-staphyloccal effects were strain-
specifi c and not as pronounced in milk as in laboratory media (Carminati and
Carini 1989; Johnson 1994). Other pathogens such as B. cereus, C. perfringens,
Campylobacter jejuni, E. coli 0157:H7, Salmonella typhimurium and Yersinia
enterocolitica have been found to be resistant in laboratory media (Hughey and
Johnson 1987).
Lysozyme is the only antimicrobial enzyme that has achieved commercial
application as a food preservative. Hen egg lysozyme is classifi ed as GRAS in the
US and is approved in Europe where it has the food additive number E1105. It is
also approved in Japan and Australia. A major application is in the control of 'late
blowing' (the formation of unsightly holes and unpleasant odours during
maturation) in cheeses such as Edam and Gouda due to growth of C. tyrobutyricum
(Scott et al. 1987; Fox and Grufferty 1991). In this application, lysozyme attacks
the vegetative cells at the start of outgrowth from the endospore. Lysozyme is
added to the milk used for cheese production at a level of 25 mg/l to give a fi nal
concentration in the cheese of 300 mg/kg (Carminati et al. 1984). Although
lysozyme has been reported to interfere slightly with the growth of some lactic
acid bacteria in cheese, this problem can be prevented by using lysozyme-resistant
starter cultures (Carminati and Carina 1989). It was estimated that, in 1984, 100
tonnes of lysozyme were used in cheese in Europe (Scott et al. 1987).
Recently it has been realised that lysozyme can reduce the heat resistance of
non-proteolytic C. botulinum spores and this has caused a degree of caution in
the possible use of lysozyme in refrigerated, processed foods with a long shelf
life. Mild heat treatments can sub-lethally damage spores of non-proteolytic
C. botulinum by inactivating the germination system. Damaged spores cannot
germinate and outgrow on some nutrient media, but if lysozyme is present, it can
diffuse through the spore coat of some spores and induce germination by
hydrolysing peptidoglycan in the spore cortex thus reviving dormant spores
previously regarded as dead (Gould 1989; Stringer and Peck 2008). This concern
highlights the need for thorough research and vigilance on unsuspected
consequences from the use of natural preservatives when applied to reduced heat-
processed products. Another potential problem is the development of resistance of
some Bacillus spp. to lysozyme and other biocides (Knott et al. 1995).

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6.3.4 Protamine
Protamine is a cationic antimicrobial peptide extracted from the sperm cells of
vertebrates including fi sh. Protamine sulphate from fi sh milt has been used in
medicine for many years mainly to retard the release of insulin and as an antidote
to heparin (Jaques 1973; Brange 1987). Protamine has antimicrobial activity
against a range of Gram-positive and negative bacteria, yeasts and moulds (Islam