Table 1.

Natural antimicrobials for food bio-preservation.

	Antimicrobials	Source	Food bio-preservation
Antimicrobial substances derived from bacterial cell metabolism	Organic acids	Main end products of fermentation.	Decrease the pH of surrounding environment, creating a selective barrier against non-acidophiles. Lactic acid exerts antimicrobial effect by disruption of the cytoplasmic membrane and interference with membrane potential.
	CO2	Heterofermentative LAB produces CO2 as a byproduct of sugar fermentation.	Creation of an anaerobic environment and antagonistic effects specifically against aerobic bacteria and produce carbonic acid.
	Diacetyl (2,3-butanedione)	LAB as a by-product of metabolic activity	Antibacterial activity against Listeria, Salmonella, Escherichia coli, Yersinia, and Aeromonas.
	Hydrogen peroxide	Produces by LAB in presence of oxygen and action of flavoprotein oxidases or NADH peroxidase.	Antibacterial effect through oxidative damage of proteins and increase of membrane permeability.
	Reuterin	Low molecular- weight antimicrobial compound produced by Lactobacillus reuteri and some other LAB.	Antimicrobial activity against bacteria as well as yeasts and molds by inhibiting DNA synthesis.
	Reutericyclin	Reutericyclin-producing strains of LAB.	Reutericyclin acts as a proton ionophore and dissipation of the proton motive force against gram-positive bacteria including Lactobacillus spp., Bacillus subtilis, Bacillus cereus, Enterococcus faecalis, Staphylococcus aureus and Listeria innocua.
Antifungal compounds	Natamycin (pimaricin)	Produced from Streptomyces natalensis	Broad-spectrum antifungal biopreservative for foods and beverages by binding irreversibly to the cell membrane of fungi and causes membrane hyperpermeability leading to rapid leakage of essential ions and peptides and ultimately cell lysis.
Antimicrobials from Animal Sources	Lysozyme	Naturally found as part of defense system of living organisms.	Generally recognized as safe (GRAS) for direct addition to foods.
	Lactoferrin	Natural protein found in milk and other secretions.	Antimicrobial activity due to its iron-binding capacity and polycationic nature against a wide range of bacteria including foodborne pathogens like Carnobacterium, Listeria monocytogenes, Escherichia coli, Klebsiella and viruses (Lönnerdal, 2011; Gyawali and Ibrahim, 2014).
	Lactoperoxidase	Antimicrobial system that originated from milk.	Effective against gram-negative bacteria.
	Ovotransferrin	Produced by hydrolysis of natural proteins.	Inhibits bacterial growth due to iron deprivation.
	Protamine	Naturally present in spermatic cells of fish, birds and mammals.	Broad antimicrobial activity against gram-positive bacteria, gram-negative bacteria, and fungi. Used as preservative in wide variety of foods ranging from confection items to fruits and rice.
	Pleurocidin	Present in myeloid cells and mucosal tissues of many vertebrates and Invertebrates.	Antimicrobial activity against several foodborne bacteria such as L. monocytogenes and E. coli O157:H7, and pathogenic fungi.
	Chitosan	Polycationic biopolymer naturally present in exoskeletons of crustaceans and arthropods.	Considered as safe food additive and has antibacterial activity against both Gram-positive and Gram-negative bacteria such as Staphylococcus aureus, Listeria monocytogenes, Bacillus cereus, E. coli, Shigella dysenteria, and Salmonella typhimurium (Gyawali and Ibrahim, 2014). Used in biodegradable edible coatings, singly or dosed with other antimicrobial substances (Elsabee et al., 2013).
Antimicrobials derived from plants	Essential oils such as saponins, flavonoids, carvacrol, thymol, citral, eugenol, linalool, terpenes, and their precursors	Plant material like flowers, buds, seeds, leaves, twigs, bark, herbs, wood, fruits and roots.	The concentration of 0.05–0.1% of essential oils has demonstrated activity against pathogens, such as Salmonella typhimurium, E. coli O157:H7, L. monocytogenes, B. cereus and S. aureus in food systems.