Control by Antimicrobial Preservatives and Bacteriophages ◾ 495
antimicrobial property of this lipophilic compound is enhanced with lactate, sorbate, ascorbate,
and nisin but may be reduced by starchy and proteinaceous compounds. In combination with
monolaurin, the fungistatic activity of several antifungal compounds is enhanced. The antimicrobial activity of monolaurin is produced through its ability to destabilize the functions of the
membrane. At lower concentrations, it is bacteriostatic by interfering with the uptake of nutrients.
It can be used up to 500 ppm without affecting the taste of the food.
Ethylene-Diamine-Tetraacetate (EDTA)
The sodium and calcium salts of EDTA at 100 ppm are approved for use in foods to chelate
trace metals in order to prevent their adverse effect on food quality. At a low dose (5000 ppm),
EDTA appears to have no toxic effect and mostly passes through the GI tract unabsorbed. By
itself, EDTA may not have much antimicrobial effect, but because of its ability to chelate divalent
cations, it can destabilize the barrier functions of the outer membrane of gram-negative bacteria
and, to some extent, the cell wall of gram-positive bacteria. In this way, it enhances antibacterial
action of other chemicals, especially those that are membrane acting, such as surface-active compounds, antioxidants, lysozymes, and bacteriocins. EDTA is also inhibitory for germination and
outgrowth of spores of Clo. botulinum. In the presence of divalent cations in the food environment
(e.g., dairy products), the effectiveness of EDTA is greatly reduced.
Antimicrobials of Microbial origin 1–4
Bacteriocins of Lactic Acid Bacteria
Bacteriocins of food-grade lactic acid bacteria, with special reference to nisin, pediocin AcH, and
reuterine and their application as food preservatives, are discussed in Chapter 17.
Natamycin
Natamycin, a microlid produced by Streptomyces natalensis, is a broad-spectrum antifungal agent.
It is amphiphilic; thus it has a lower solubility in water than bacteriocins. Its use as a dip or
spray to prevent growth of molds and formation of mycotoxins on the surface of some cheeses,
sausages, and in raw peanuts has been approved by the Expert Committee of the World Health
Organization (WHO). It is customarily used at 500 ppm, which leaves detectable but safe levels
of the antibiotic on the product surface. It is also effective against fungal growth on fruits such
as strawberries, cranberries, and raspberries. Natamycin binds to ergosterol on the fungal cell
membrane and increases membrane permeability, leakage of essential ions and cell lysis. Because
bacteria do not have sterol on their membrane, natamycin is ineffective against them.
Tylosin
Tylosin, a microlid produced by Streptomyces, inhibits protein synthesis, is a bactericidal antibiotic
that is more effective against gram-positive than gram-negative bacteria and also inhibits outgrowth of germinated endospores. Because of its high heat resistance, it has been studied at a low
concentration (1 ppm) to determine its effectiveness in controlling the growth of spore formers in
low-acid canned products.
antimicrobial property of this lipophilic compound is enhanced with lactate, sorbate, ascorbate,
and nisin but may be reduced by starchy and proteinaceous compounds. In combination with
monolaurin, the fungistatic activity of several antifungal compounds is enhanced. The antimicrobial activity of monolaurin is produced through its ability to destabilize the functions of the
membrane. At lower concentrations, it is bacteriostatic by interfering with the uptake of nutrients.
It can be used up to 500 ppm without affecting the taste of the food.
Ethylene-Diamine-Tetraacetate (EDTA)
The sodium and calcium salts of EDTA at 100 ppm are approved for use in foods to chelate
trace metals in order to prevent their adverse effect on food quality. At a low dose (5000 ppm),
EDTA appears to have no toxic effect and mostly passes through the GI tract unabsorbed. By
itself, EDTA may not have much antimicrobial effect, but because of its ability to chelate divalent
cations, it can destabilize the barrier functions of the outer membrane of gram-negative bacteria
and, to some extent, the cell wall of gram-positive bacteria. In this way, it enhances antibacterial
action of other chemicals, especially those that are membrane acting, such as surface-active compounds, antioxidants, lysozymes, and bacteriocins. EDTA is also inhibitory for germination and
outgrowth of spores of Clo. botulinum. In the presence of divalent cations in the food environment
(e.g., dairy products), the effectiveness of EDTA is greatly reduced.
Antimicrobials of Microbial origin 1–4
Bacteriocins of Lactic Acid Bacteria
Bacteriocins of food-grade lactic acid bacteria, with special reference to nisin, pediocin AcH, and
reuterine and their application as food preservatives, are discussed in Chapter 17.
Natamycin
Natamycin, a microlid produced by Streptomyces natalensis, is a broad-spectrum antifungal agent.
It is amphiphilic; thus it has a lower solubility in water than bacteriocins. Its use as a dip or
spray to prevent growth of molds and formation of mycotoxins on the surface of some cheeses,
sausages, and in raw peanuts has been approved by the Expert Committee of the World Health
Organization (WHO). It is customarily used at 500 ppm, which leaves detectable but safe levels
of the antibiotic on the product surface. It is also effective against fungal growth on fruits such
as strawberries, cranberries, and raspberries. Natamycin binds to ergosterol on the fungal cell
membrane and increases membrane permeability, leakage of essential ions and cell lysis. Because
bacteria do not have sterol on their membrane, natamycin is ineffective against them.
Tylosin
Tylosin, a microlid produced by Streptomyces, inhibits protein synthesis, is a bactericidal antibiotic
that is more effective against gram-positive than gram-negative bacteria and also inhibits outgrowth of germinated endospores. Because of its high heat resistance, it has been studied at a low
concentration (1 ppm) to determine its effectiveness in controlling the growth of spore formers in
low-acid canned products.