Natural Antimicrobial Agents

Based on the origins, natural antimicrobials can be further classified as animal, plant, and microbial sources. There activity against bacteria and fungi was summarized in Table 5.2.

Animal Sources

Chitosan

Chitosan, a linear polysaccharide, is the N-deacetylation product of chitin, the byproduct of shellfish processing. Chitosan comprises a series of polymers with differing ratios of glucosamine and N-acetyl glucosamine units via в (1—4) linkage. Chitosan has been reported to have antimicrobial activities against foodborne fungi and bacteria, with minimum inhibition concentration (MIC) varying from 0.01% to 5%, depending on the source of chitosan, charge density, the molecular weight, degree of deacetylation, pH, temperature, ionic strength, concentration, derivatives of chitosan, complex with certain materials, type of microorganisms, and food components (Hosseinnejad and Jafari, 2016; Kong et al., 2010). Up to now, four models have been proposed to explain the antimicrobial activity of chitosan (Goy et al., 2009; Hosseinnejad and Jafari, 2016; Kong et al., 2010): (1) the electrostatic interaction between positively charged chitosan molecules and negatively charged microbial cell membranes, causing the change of membrane permeability and hydrolysis of peptidoglycans in the microorganism wall. This is the most acceptable one. (2) The penetration of chitosan into

TABLE 5.2 Antimicrobial Spectrum of Selected Natural Antimicrobial Agents

Sources

Compound

Bacteria Inhibited

Fungi Inhibited

Gram-positive

Bacteria

Gram-negative

Bacteria

Animal

Chitosan

L. monocytogenes Bacillus cereus Staphylococcus aureus

E. coli

E. coli O157:H7

Salmonella

typhimurium

Zygosaccharomyces

bailii

Lysozyme

B. stearothermophilus B. cereus Lactobacillus spp.

L. monocytogenes

C. jejuni E. coli

E. coli O157:H7 Pseudomonas aeruginosa S. enteritidis Y. enterocolitica

Aspergillus

Candida

Fusarium

Graminearum

Paecilomyces

Penicillium

Saccharomyces

Lactoferrin

B. subtilis

B. stearothermophilus, L. monocytogenes

E. coli

E. coli O157:H7 S. enteritidis

Plant

Basil oil

Shigella sonnei Bacillus Enterococcus Staphylococcus

S. flexneri E. coli S. enteritidis Pseudomonas Vibrio

parahaemolyticus

Aspergillus

Candida

Geotrichum

candidum

Thyme oil

Shigella sonnei S. aureus

L. monocytogenes Lactic acid bacteria

S. flexneri E. coli

E. coli O157:H7 S. enteritidis S. typhimurium Y. enterocolitica

Botrytis cinerea C. albicans P. digitatum Rhizopus stolonifer

Clove bud oil

L. monocytogenes S. epidermidis S. aureus

C.jejuni E. coli S. enteritidis

C. albicans

Trichophyton

mentagrophytes

Oregano oil

L. monocytogenes B. subtilis

S. aureus (methicillin- resistant)

S. aureus

E. coli

E. coli O157:H7 P. aeruginosa S. enterica S. enteritidis S. typhimurium

C. albicans P. digitatum S. cerevisiae

Tea tree oil

B. cereus,

S. aureus (methicillin resistant);

L. monocytogenes B. subtilis

Acinetobacter baumannii E. coli

E. coli O157:H7 S. flexneri S. choleraesuis

A. flavus C. albicans Cryptococcus neoformans

Rosemary

extract

Streptococcus agalactiae L. monocytogenes, Lactococcus lactis S. aureus

P. putida E. coli Klebsiella pneumoniae

Aspergillus Saccharomyces cerevisiae C. albicans

(Continued)

TABLE 5.2 (Continued)

Sources

Compound

Bacteria Inhibited

Fungi Inhibited

Gram-positive

Bacteria

Gram-negative

Bacteria

B. megaterium B. subtilis

Enterococcus faecalis

Proteus mirabilis

P. pastoris

Arrowroot tea extract

L. monocytogenes S. aureus

E. coli O157:H7 S. enterica

Grapefruit seed extract

B. subtilis Micrococcus flavus S. aureus

Serratia marcescens

E. coli P. mirabilis

C. maltose

Olive leaf extract

S. aureus B. cereus B. subtilis E. faecalis Kocuria rhizophila Lactobacillus acidophilus L. casei

L. spp.

L. innocua L. monocytogenes Micrococcus luteus S. aureus (methicillin resistant)

S. capitis S. epidermidis S. hominis

E. coli

Acinetobacter calcoaceticus C. jejuni Helicobacter pylori

K. pneumoniae P. aeruginosa S. enterica Serratia marcescens

C. albicans C. glabrata C. parapsilosis C. oleophila Schizosaccharomyces pombe

Microbial

Nisin

Listeria

Staphylococcus

Bacillus

Clostridium

Enterococcus

Lactococcus

Spores formed by

bacteria such as Bacillus

and Clostridium

No effect

Natamycin

No effect

No effect

Penicillium candidum A. flavus S. cerevisiae Byssochlamys nivea Hemerocallis fulva Zygosaccharomyces bailii

the nuclei of microorganisms results in the binding of chitosan with microbial DNA and thereof prevents the RNA transformation and protein synthesis. (3) The chelation of chitosan with metals, the suppression of spores and binding to essential nutrients inhibit the microbial growth. (4) chitosan forms a polymer membrane on the surface of the cell. This membrane could prevent nutrients from entering the cell or block oxygen from the cells which can inhibit the growth of aerobic bacteria. Chitosan is a great polymer candidate for biofilm formation. Therefore, it has been widely used for biofilm formation. The films consisting of chitosan have been evaluated to extend the shelf life of ground meat (Dehnad et al., 2014), fish fillets (Kakaei and Shahbazi, 2016), fruits (Jongsri et al., 2016), and vegetables (Bilbao-Sainz et al., 2016).

 
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