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The small rods shown here are lactic acid bacteria which convert lactose and other sugars to lactic acid. The produts of their metabolism can have benign preservative effects.

3D stick model of nisin, a particularly effective preservative produced by some lactic acid bacteria.

BioPreservation

Biopreservation is the use of natural or controlled microbiota or antimicrobials as a way of preserving food and extending its shelf life. The bio-preservation of food, especially utilizing lactic acid bacteria (LAB) that are inhibitory to food spoilage microbes, has been practiced since early ages, at first unconsciously but eventually with an increasingly robust scientific foundation. Beneficial bacteria or the fermentation products produced by these bacteria are used in biopreservation to control spoilage and render pathogens inactive in food. There are a various mode of actions through which microorganisms can interfere with the growth of others such as organic acid production, resulting in a reduction of pH and the antimicrobial activity of the un-dissociated acid molecules, a wide variety of small inhibitory molecules including hydrogen peroxide, diacetyl, hypothiocyanate, reuterin and bacteriocins, sometimes powerfully active against pathogens and food spoilage organisms and also competition for space and essential nutrients, as well as the action of bacteriophages.

Lactic acid bacteria

Of special interest are lactic acid bacteria (LAB). Lactic acid bacteria have antagonistic properties which make them particularly useful as biopreservatives. When LABs compete for nutrients, their metabolites often include active antimicrobials such as lactic and acetic acid, hydrogen peroxide, and peptide bacteriocins. Some LABs produce the antimicrobial nisin which is a particularly effective preservative. In addition to lactic acid bacteria, yeasts also have been reported to have biopreservation effect due to their antagonistic activities relying on the competition for nutrients, production and tolerance of high concentrations of ethanol, as well as the synthesis of a large class of antimicrobial compounds exhibiting large spectrum of activity against food spoilage microorganisms, but also against plant, animal and human pathogen.

A bacterium that is a suitable candidate for use as a biopreservative does not necessarily have to ferment the food. But if conditions are suitable for microbial growth, then a biopreservative bacterium will compete well for nutrients with the spoilage and pathogenic bacteria in the food. As a product of its metabolism, it should also produce acids and other antimicrobial agents, particularly bacteriocins. Biopreservative bacteria, such as lactic acid bacteria, must be harmless to humans. These days LAB bacteriocins are used as an integral part of hurdle technology. Using them in combination with other preservative techniques can effectively control spoilage bacteria and other pathogens, and can inhibit the activities of a wide spectrum of organisms, including inherently resistant Gram-negative bacteria." Lactic acid bacteria and propionibacteria have been extensively studies for their efficacy against spoilage causing yeasts and molds in food spoilage.

Bacteriophages

Bacteriophages (Greek for 'bacteria eater') or simply phages are viruses which infect bacteria. The majority of all bacteriophages known exhibit a double stranded DNA genome inside the virion capsid and belong to the order of tailed phages (Caudovirales). The tailed phages can be further separated into three families: Podoviridae are characterized by very short tails, Myoviridae exhibit longer, straight and contractile tails, and Siphoviridae can be identified due to their long and flexible tails. Another well studied group of phages with many applications (although minor in terms of species diversity) is represented by filamentous phages which exhibit a single stranded DNA genome decorated by a helical protein layer surrounding the DNA molecule. The idea of using phages as an agent against unwanted bacteria developed shortly after their discovery. With the improvements in organic chemistry during the 1950s, exploration and development of broad spectrum antibiotics displaced interest in bacteriophage research. Several laboratories have been testing suitability of bacteriophage isolates to control certain bacterial pathogens. Tremendous amount of research was added in this field at the Bacteriophage Institute in Tbilisi, Georgia, where phage therapy is routinely applied in medicine research field. Today treatment of antibiotic resistant bacteria is a challenging task. Due to severe problems in treatment of infectious diseases caused by (multiple) antibiotic resistant pathogens, the application of antibiotics is not effectively working, therefore research on the application of bacteriophages is being reviewed intensely.

Meat Biopreservation

In meat processing, biopreservation has been extensively studies in fermented meat products and ready to eat meat products. The use of native or artificially-introduced microbial population to improve animal health and productivity, andlor to reduce pathogenic organisms, has been termed a 'probiotic' or competitive enhancement approach. Competitive enhancement strategies that have been developed include competitive exclusion, addition of a microbial supplement (probiotic) that improves gastrointestinal health and adding a limiting, non-host digestible nutrient (prebiotic) that provides an existing (or introduced) commensal microbial population a competitive advantage in the gastrointestinal tract. <ref name="Lacroix8"> Each of these approaches utilizes the activities of the native microbial ecosystem against pathogens by capitalizing on the natural microbial competition. Generally speaking, competitive enhancement strategies offer a natural 'green' method to reduce pathogens in the gut of food animals. <ref name="Lacroix8">