Bacteriocin-based Strategies for Food Biopreservation

In this review, antimicrobials from a range of plant, animal, and microbial sources are reviewed along with their potential applications in food systems. Chemical and biochemical antimicrobial compounds derived from these natural sources and their activity against a range of pathogenic and spoilage microorganisms pertinent to food, together with their effects on food organoleptic properties, are outlined. Factors influencing the antimicrobial activity of such agents are discussed including extraction methods, molecular weight, and agent origin. These issues are considered in conjunction with the latest developments in the quantification of the minimum inhibitory (and noninhibitory) concentration of antimicrobials and/or their components. Natural antimicrobials can be used alone or in combination with other novel preservation technologies to facilitate the replacement of traditional approaches. Research priorities and future trends focusing on the impact of product formulation, intrinsic product parameters, and extrinsic storage parameters on the design of efficient food preservation systems are also presented.

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Application of Natural Antimicrobials for Food Preservation

Antimicrobials are classified as traditional when they (i) have been used for many years, (ii) are approved by many countries for inclusion as antimicrobials in foods (e.g., lysozyme and lactoferrin, which are naturally occurring but regulatory-agency approved), or (iii) are produced by synthetic means (as opposed to natural extracts). Many organic acids are used as food additives, but not all have antimicrobial activity. Research suggests that the most active are acetic, lactic, propionic, sorbic, and benzoic acids. Acetic acid was the most effective antimicrobial in ground roasted beef slurries against Escherichia coli O157:H7 growth in comparison with citric or lactic acid. Sorbate is applied to foods by direct addition, dipping, spraying, dusting, or incorporation into packaging. The mechanism by which dimethyl dicarbonate (DMDC) acts is most likely related to inactivation of enzymes. A related compound, diethyl dicarbonate, reacts with imidazole groups, amines, or thiols of proteins. Lysozyme is most active against gram-positive bacteria, most likely because the peptidoglycan of the cell wall is more exposed. The primary use for sodium nitrite as an antimicrobial is to inhibit Clostridium botulinum growth and toxin production in cured meats. Sulfites may be used to inhibit acetic acid-producing bacteria, lactic acid bacteria, and spoilage bacteria in meat products. In the future, traditional food antimicrobials will continue to play an important role in food preservation.

Chemical Preservatives and Natural Antimicrobial Compounds

Over the last 2 decades, a variety of bacteriocins, produced by bacteria that kill or inhibit the growth of other bacteria, have been identified and characterized biochemically and genetically. This review article focuses on the ecology of bacteriocins, determination of bacteriocin activity, biosynthesis of bacteriocins, and mode of action. Bacteriocin production and modeling are discussed in the article. Nisin is discussed in some detail in this article since it is currently the only purified bacteriocin approved for food use in the U.S. and has been successfully used for several decades as a food preservative in more than 50 countries. For activity spectra and food applications, the review article focuses primarily on class I and class IIa bacteriocins produced by lactic acid bacteria (LAB) given their development as food preservatives.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1541-4337.2003.tb00016.x

Bacteriocins and their Food Applications

Nisin is a natural preservative for many food products. This bacteriocin is mainly used in dairy and meat products. Nisin inhibits pathogenic food borne bacteria such as Listeria monocytogenes and many other Gram-positive food spoilage microorganisms. Nisin can be used alone or in combination with other preservatives or also with several physical treatments. This paper reviews physicochemical and biological properties of nisin, the main factors affecting its antimicrobial effectiveness, and its food applications as an additive directly incorporated into food matrices.

Nisin as a Food Preservative: Part 1: Physicochemical Properties, Antimicrobial Activity, and Main Uses

The effects of nisin and monolaurin, alone and in combination, were investigated on Bacillus licheniformis spores in milk at 37 degrees C. In the absence of inhibitors, germinated spores developed into growing vegetative cells and started sporulation at the end of the exponential phase. In the presence of nisin (25 IU ml-1), spore outgrowth was inhibited (4 log10 reduction at 10 h). Regrowth appeared between 10 and 24 h and reached a high population level (1.25 x 10(8) cfu ml-1) after 7 d. Monolaurin (250 micrograms ml-1) had a bacteriostatic effect during the first 10 h but thereafter, regrowth occurred slowly with a population level after 7 d (4 x 10(5) cfu ml-1) lower than that of nisin. Different combined effects of nisin (between 0 and 42 IU ml-1), monolaurin (ranging from 0 to 300 micrograms ml-1), pH values (between 5.0 and 7.0) and spore loads (10(3), 10(4), 10(5) spores ml-1) were investigated using a Doehlert matrix in order to study the main effects of these factors and the different interactions. Results were analysed using the Response Surface Methodology (RSM) and indicated that nisin and monolaurin had no action on spores before germination; only pH values had a significant effect (P < or = 0.001), i.e. spore count decreased as the pH value increased in relation to germination. Sublethal concentrations of nisin (30 IU ml-1) and monolaurin (100 micrograms ml-1) in combination acted synergistically on outgrown spores and vegetative cells, showing total inhibition at pH 6.0, without regrowth, within 7 d at 37 degrees C.

Inhibition of Bacillus licheniformis spore growth in milk by nisin, monolaurin, and pH combinations

Inhibitory combinations of nisin, sodium chloride, and pH on Listeria monocytogenes ATCC 15313 in broth by an experimental design approach.

An inhibitory synergistic effect of a nisin–monolaurin combination on Bacillus sp. vegetative cells in milk

Combined efTects of nisin, Iactic acid, and potassium sorbate on Baeil/us liche- niformis spores in milk. The inhibitory activities of nisin and/or potassium sorbate on Bacillus licheniformis spores were studied in milk acidified with lactic acid, at 37 oc.Three experimen- tal plans were realized using the Doehlert uniform shell design. Spore germination, pH-dependent, was enhanced as the pH increased. Nisin had no sporicidal effect, but inhibited the growth of ger- minated spores. Its bactericidal activity increased with the concentration of nisin and as the pH and the initial spore load decreased. Potassium sorbate was not sporicidal but disturbed the spore germination at high concentrations and low pH values. Its bactericidal effect was favoured at aci- dic pH values. Nisin and sorbate potassium in association enhanced the bactericidal effect with an important inhibition at high pH values. © Inra/Elsevier, Paris. Bacil/us licheniformis / spore / nisin / potassium sorbate / lactic acid

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Marianne Mansour

Papers

Inhibition of Bacillus licheniformis spore growth in milk by nisin, monolaurin, and pH combinations

Inhibitory combinations of nisin, sodium chloride, and pH on Listeria monocytogenes ATCC 15313 in broth by an experimental design approach.

An inhibitory synergistic effect of a nisin–monolaurin combination on Bacillus sp. vegetative cells in milk

Effets combinés de la nisine, de l'acide lactique et du sorbate de potassium sur les spores de Bacillus licheniformis dans le lait