496 ◾ Fundamental Food Microbiology
Polylysine
Polylysine is produced by Streptomyces actinomycetes and is inhibitory to gram-positive and gramnegative bacteria including Lis. monocytogenes, Salmonella, Esc. coli O157:H7 and fungi. It is thermostable (100°C for 100 minutes or 120°C for 20 minutes), active in a wide range of pH, and
water soluble and does not affect food flavor. It is widely used in Japan as a food preservative.
Antimicrobials of Animal origin 1,3
Chitosan
Chitosan, a polycationic polymer [poly (β-1,4)-2-amino-2-deoxy-d-glucopyranose], is obtained
by alkaline hydrolysis of chitin from the shells of Crustaceans, such as shellfish and arthropods.
It is inhibitory against bacteria, yeasts, and molds and causes destabilization of the cell wall and
cell membrane functions. It is safe for human consumption. It has many applications in foods,
including direct application into product formulations to improve shelf-life and also into packaging film to prevent microbial growth on the surface of products. It has low solubility in water;
thus, it is dissolved in organic acids (acetic or lactic acid) for use during food processing. Acidic
conditions may hydrolyze chitosan, so modified water-soluble stable derivatives have been developed. Chitosan coating on eggs prevented Salmonella Enteritidis, Esc. coli, and Lis. monocytogenes
growth. Chitosan-based edible packaging films prepared in combination with essential oils and
nisin protected the meat surface from growth of Lis. monocytogenes and Esc. coli O157:H7.
Lysozyme
The enzyme lysozyme (a muramidase) is present in large quantities in some foods, such as egg
whites and shellfish (oysters and clams), as well as in small amounts in milk and some plant tissues.
It is also abundant in human saliva and other body fluids. It hydrolyzes the peptidoglycan (β-1,4
linkage between N-acetylmuramic acid and N-acetyl-glucosamine) layer present in the cell wall of
gram-positive and gram-negative bacteria. In gram-negative bacteria the cell wall is located in the
middle layer and lysozyme is effective only after the barrier function of the outer membrane (OM)
is destabilized by chemical (e.g., EDTA) and physical (e.g., freezing or heating) stresses. The antimicrobial effect is manifested by the lysis of cells. Lysozyme is most effective at pH 6.0–7.0 and
at concentrations of approximately 0.01%–0.1%. It can be used directly to control gram-positive
bacteria and with EDTA and other similar compounds to control gram-negative bacteria. It has
been used in wine (sake, a Japanese beverage) to prevent growth of undesirable lactic acid bacteria
and in tuna and salmon products to control Lis. monocytogenes.
Lactoferrin
Lactoferrin, an iron-binding glycoprotein is naturally present in milk and also in human and animal tissues and body fluids. It a has broad-spectrum antimicrobial effect against bacterial and viral
pathogens. Besides, in humans and animals, it regulates immune function, intestinal proliferation,
and facilitates iron adsorption. Its antimicrobial action depends on binding to the surface of bacteria, such as the outer membrane of gram-negative bacteria leading to damaged OM. Lactoferrin
has a strong affinity for iron, rendering it unavailable for bacterial metabolism and thus preventing
bacterial growth. It is now approved by USDA-FSIS for use on a variety of meat products.
Polylysine
Polylysine is produced by Streptomyces actinomycetes and is inhibitory to gram-positive and gramnegative bacteria including Lis. monocytogenes, Salmonella, Esc. coli O157:H7 and fungi. It is thermostable (100°C for 100 minutes or 120°C for 20 minutes), active in a wide range of pH, and
water soluble and does not affect food flavor. It is widely used in Japan as a food preservative.
Antimicrobials of Animal origin 1,3
Chitosan
Chitosan, a polycationic polymer [poly (β-1,4)-2-amino-2-deoxy-d-glucopyranose], is obtained
by alkaline hydrolysis of chitin from the shells of Crustaceans, such as shellfish and arthropods.
It is inhibitory against bacteria, yeasts, and molds and causes destabilization of the cell wall and
cell membrane functions. It is safe for human consumption. It has many applications in foods,
including direct application into product formulations to improve shelf-life and also into packaging film to prevent microbial growth on the surface of products. It has low solubility in water;
thus, it is dissolved in organic acids (acetic or lactic acid) for use during food processing. Acidic
conditions may hydrolyze chitosan, so modified water-soluble stable derivatives have been developed. Chitosan coating on eggs prevented Salmonella Enteritidis, Esc. coli, and Lis. monocytogenes
growth. Chitosan-based edible packaging films prepared in combination with essential oils and
nisin protected the meat surface from growth of Lis. monocytogenes and Esc. coli O157:H7.
Lysozyme
The enzyme lysozyme (a muramidase) is present in large quantities in some foods, such as egg
whites and shellfish (oysters and clams), as well as in small amounts in milk and some plant tissues.
It is also abundant in human saliva and other body fluids. It hydrolyzes the peptidoglycan (β-1,4
linkage between N-acetylmuramic acid and N-acetyl-glucosamine) layer present in the cell wall of
gram-positive and gram-negative bacteria. In gram-negative bacteria the cell wall is located in the
middle layer and lysozyme is effective only after the barrier function of the outer membrane (OM)
is destabilized by chemical (e.g., EDTA) and physical (e.g., freezing or heating) stresses. The antimicrobial effect is manifested by the lysis of cells. Lysozyme is most effective at pH 6.0–7.0 and
at concentrations of approximately 0.01%–0.1%. It can be used directly to control gram-positive
bacteria and with EDTA and other similar compounds to control gram-negative bacteria. It has
been used in wine (sake, a Japanese beverage) to prevent growth of undesirable lactic acid bacteria
and in tuna and salmon products to control Lis. monocytogenes.
Lactoferrin
Lactoferrin, an iron-binding glycoprotein is naturally present in milk and also in human and animal tissues and body fluids. It a has broad-spectrum antimicrobial effect against bacterial and viral
pathogens. Besides, in humans and animals, it regulates immune function, intestinal proliferation,
and facilitates iron adsorption. Its antimicrobial action depends on binding to the surface of bacteria, such as the outer membrane of gram-negative bacteria leading to damaged OM. Lactoferrin
has a strong affinity for iron, rendering it unavailable for bacterial metabolism and thus preventing
bacterial growth. It is now approved by USDA-FSIS for use on a variety of meat products.