Editorial Article

Antimicrobials in food and the role of Bacteriocins

Dr. Giorgia Caruso,
Contract Researcher, Istituto Zooprofilattico Sperimentale, Palermo, Italy.
Email: giorgia.cars@gmail.com
At present, the food business is compelled to tackle different challenges with relation to food safety, consumers’ demands, and new regulatory norms on the international level. In particular, the consumers’ awareness for natural healthy products has increased, but at the same time food industry has to face risks deriving from microbial contaminations.
*Corresponding author:

Dr. Giorgia Caruso
Email: giorgia.cars@gmail.com

At present, the food business is compelled to tackle different challenges with relation to food safety, consumers’ demands, and new regulatory norms on the international level. In particular, the consumers’ awareness for natural healthy products has increased, but at the same time food industry has to face risks deriving from microbial contaminations.

The toxic effect of many chemical additives has become more popular, hence research has recently been impelled to find an adequate solution. Antimicrobial packaging with natural substances and natural biodegradable polymer films is a very promising improvement, satisfying the sustainability requirement of consumers. The application of bacteriocins has allowed to overcome this disadvantage, thus it has aroused interest in the food system since bacteriocins have been provided the GRAS (Generally Regarded As Safe) status, and can be used as bio- preservatives (Cotter et al 2005). Bacteriocins are produced by the majority of groups of bacteria. Specifically, lactic acid bacteria (LAB) are present in numerous food products and have always been widely utilized in the production of fermented products, so they are considered safe for human consumption (Ameen & Caruso 2017). Bacteriocins are ribosomally synthesized antimicrobial proteins which may have evolved for space and resource competition with other bacteria in the environment. In fact, they possess an antibacterial activity consisting in various mechanisms that alter the cell membrane permeability properties, as cytoplasmic membrane pore formation and cell wall interference. These peculiar bacteriocins show a notable thermal resistance; in addition, they can operate in a wide pH range. Furthermore, for their proteinaceous nature they can be degraded by proteolytic enzymes. As a result, target microorganisms have reduced possibilities of developing antibiotic resistance in these conditions (Cotter et al 2013). Numerous bacteriocins have been tested for their application as food preservatives and some are already commercially available, like nisin, a bacteriocin of Lactobacillus lactis, lactocin produced by strain of L. curvatus and pediocin PA-1/AcH, a bacteriocin of Pedicococcus acidilactici (Tong et al 2014). They can be added in concentrated preparations, or they can be produced in situ by LAB starter cultures. It has been shown that the combination of bacteriocins with hurdle technology treatments potentiates the antimicrobial activity. Usage of non-thermal treatments, for instance Pulsed Electric Field (PEF), together with bacteriocins, has proved beneficial in controlling pathogens (Sobrino-Lopez & Martin Belloso 2006). Recently, bioactive packaging has emerged as another application of bacteriocins. Bioactive packaging can be used either incorporating bacteriocins directly into polymers or into packaging films through coating or adsorbing bacteriocins to the surface of polymers, as biodegradable protein films (Appendini & Hotchkiss 2002). The latter process may be achieved by heat press or adsorption of bacteriocin on certain polymeric materials (Zacharof & Lovitt 2012). In various types of meat, bacteriocins from L. curvatus immobilized in polyethylene film reduced the microbial counts of L. monocytogenes during shelf life storage (Ercolini et al 2006); according to Okuda et al (2013), the potent antibiotic vancomycin was found to be less effective on MRSA (methicillin-resistant Staphylococcus aureus) planktonic and biofilm cells, in respect to some bacteriocins (i.e. nisin A and lacticin Q), which had a stronger bactericidal activity. Polyvinyl alcohol films carrying nisin inactivated L. monocytogenes for 90-day storage in fermented sausages (Marcos et al 2013). Nisin coating embedded in a cellophane-based packaging decreased total aerobic bacteria counts in chopped meat for more than 10 days at refrigeration temperature (Guerra et al 2005). Antimicrobial packaging provides additional efficiency over cell fermentation in situ (increased productivity, longer stability and greater process control) and also over the direct incorporation of bacteriocin in the food product. In fact, for instance the immobilization technique in packaging allows a slower release of the antimicrobial compound in food and the protection of the antimicrobial activity when exposed to proteolysis (Bali et al 2014; Le-Tien et al 2004). Immobilization may be carried out by different methods: adsorption, which is characterized by low reproducibility, as is based on reversible weak forces, as hydrophobic interactions and van der Walls forces (Guisan 2006), ionic binding in which the molecule is charged, resulting in a more electrostatically stable complex, entrapment, which involves inclusion of bacteriocins within the pore system of the matrix and microencapsulation in a semi-permeable membrane characterized by a controlled porosity. However, the efficiency of bacteriocin and its release depend on the physico-chemical characteristics of the food matrix. Temperature, water activity and pH are crucial factors, hence different levels of microbial inhibition may be observed by using different food products (Coma 2008; Katla et al 2002). For instance release of bacteriocin from the film is affected by a higher temperature, and also food pH may influence the characteristics of bacteriocins by ionization (Mauriello et al 2005). Nisin has a higher solubility at lower pH, resulting in more diffusion from packaging material.

Lately the use of bacteriocins has also shifted, including a diverse array of applications, extending even to the biomedical field (Shin et al 2016). Different studies have reported the potential of nisin and its bioengineered variants against foodborne and nonfood-related pathogens (Field et al 2012), and also in human diseases (Balciunas et al 2013).

In conclusion, it is then extremely important to continue studying and exploring the varied field of bacteriocins, for widening our reserve of antimicrobial compounds for a better control of food and clinical pathogens. Therefore more research is needed, concerning toxicological aspects and safety evaluations of new bacteriocin molecules.

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Published: 26 June 2017


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