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Bacteriocins and HurdleTechnology

Gagandeep Singh

M.Tech Bio-techUIET,KURUKSHETRA UNIVERSITY2510819


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Bacteriocins

Bacteriocins are ribosomally-synthesizedpeptides or proteins with antimicrobial activity.

Many lactic acid bacteria (LAB) producebacteriocins with rather broad spectra of

inhibition Bacteriocins can be regarded as antibiotics,

but they differ from antibiotics in severalcritical ways:

Ribosomally synthesized Host cells are immune to them


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Bacteriocins

Mode of action is different from antibiotics

Target cell wall

Producers: Gram-positive and Gram-negativebacteria

Have narrow bactericidial spectrum andusually are active against closely relatedspecies .


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Bacteriocins and food systems

Foods can be supplemented with ex situproduced bacteriocin preparations, orinsitubacteriocin production.

Ex situ produced bacteriocins can also beadded in the form of raw concentratesobtained by cultivation of the producerstrain in a food-grade substrate (such asmilk or whey). The resulting preparations

may be regarded as food additives oringredients from the legal point of view.


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Bacteriocins and foodsystems

Ex situproduced bacteriocins can also beapplied in the formof immobilized

preparations, in which the partially-purifiedbacteriocin or the concentrated cultured

broth is bound to a carrier.

The carrier acts as a reservoir and diffuserof the concentrated bacteriocin moleculesand also protect the bacteriocin from

inactivation by interaction with foodcomponents and enzymatic inactivation.

Bacteriocinogenic strains can be used Insitu either directly as starter cultures, as

adjunct or co-cultures in combination witha starter culture or as rotective cultures


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Bacteriocins and food

systemsIn situ bacteriocin production

offers several advantagescompared to ex situ production

regarding both legal aspects andcosts


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Bacteriocins and Hurdle

technologyHurdle technology is a method of ensuring thatpathogens in food products can be eliminated orcontrolled by combining more than oneapproach.

The concept of hurdle technologybegan to apply in the food industry ina rational way after the observationthat survival of microorganismsgreatly decreased when they wereconfronted with multiple antimicrobialfactors.


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Need of Hurdle technology

After exposure of a bacterialpopulation to a single antimicrobialfactor there is often a heterogeneousresponse, A fraction of the population

may receive a lethal dose of theantimicrobial factor, leading to celldeath. The remaining fraction maysurvive due to several reasons:

receiving a sub-lethal dose.showing an increased resistance

because of its physiological state (e.g.stationary phase cells, or cells alreadystressed in response to otherunfavourable environmental


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Cells naturally resistant to the antimicrobialagent.

Sub-lethally injured cells as well as cells withincreased resistance may repair the damage

caused by the antimicrobial agent and survive.On the other hand the probabilities for survival

and proliferation for cells confronted withmultiple hurdles are very low.

In addition, the synergy between different

antimicrobial factors may allowthe use of lowerdoses compared to their individual application.


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Hurdle technology include1. Combination of bacteriocins with chemical

substances and natural antimicrobials.

2. Bacteriocins and heat treatments.

3. Bacteriocins and modified atmospherepackaging.

4. Bacteriocins and pulsed electric fields.

5. Bacteriocins and high hydrostatic pressure

(HHP)


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Combination of bacteriocins with chemicalsubstances and natural antimicrobials

The presence of NaCl enhanced theantimicrobial action of bacteriocinssuch as nisin,leucocin F10, enterocinAS-48 and others.

The protective effect of sodiumchloride may be due to interferencewith ionic interactions betweenbacteriocin molecules and charged

groups involved in bacteriocin bindingto target cells.


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Combination of bacteriocins withchemical substances and natural

antimicrobials

Sodium chloride may also induceconformational changes of bacteriocins orchanges in the cell envelope of the targetorganisms.

Addition of nitrite also increased the anti-listeria activity of bacteriocinogeniclactobacilli in meat and the activities ofenterocin EJ97 against

L.monocytogenes,Bacillus coagulans andBacillus macroides and enterocin AS-48againstB. cereus.


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Organic acids and their salts can potentiatethe activity of bacteriocins greatly, whileacidification enhances the antibacterialactivity of both organic acids and

bacteriocins.The increase in net charge of bacteriocins

at low pH might facilitate translocation ofbacteriocin molecules through the cell wall.

The solubility of bacteriocins may alsoincrease at lower pH, facilitating diffusionof bacteriocin molecules.


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The sensitivity ofL. monocytogenes tonisin (400 IU/ml) increased in combinationwith lactate.

The production of Ricotta-type cheeses, thecombination of nisin with acetic acid andsorbate controlledL.monocytogenescontamination over a long period storage(70 days) at 68C

Other antimicrobial compoundssuch as ethanol can actsynergistically with nisin to reducethe survival ofL. monocytogenes


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Bacteriocins and heat

treatmentsBacteriocins can be used to reduce the

intensity of heat treatments in foodswithout compromising microbial

inactivation. Nisin and heat actsynergistically against L. plantarum andL.monocytogenes.

Bacteriocins can also provide an additional

protection during food storage againstproliferation of endospores surviving heattreatments.

saving costs in the heat treatment and

decreasing the impact of heat on the food.


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Bacteriocins and modified

atmosphere packagingModified atmosphere packaging (MAP) is

frequently used in the food industry toprolong the shelf life of perishable foodproducts.

It has been reported that nisin and CO2atmosphere acted synergistically on thecytoplasmic membrane ofL.

monocytogenesby enhancing membranepermeabilization.

Growth ofL. monocytogenes wascompletely inhibited on pork immersed in

10 IU/ml nisin and packed in 80%


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Bacteriocins and pulsed

electric fieldsPulsed electric field (PEF) technology is a non-

thermal process where microbial inactivation isachieved by application of high-voltage pulses

between a set of electrodes.

PEF could also be applied to extend theantimicrobial spectrum of bacteriocins, sincePEF disrupts the bacterial outer membrane

allowing bacteriocin molecules to reach thebacterial cytoplasmic membrane target


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Bacteriocins and highhydrostatic pressure

(HHP)High hydrostatic pressure (HHP) is

an innovative food processing and

preservation method that causesinjury and killing of microbial cells.

But during pressurization, the disruption ofH-bonds, ionic bonds and hydrophobic

interactions of the macromoleculesadversely affects their structures andfunctions.

Since most bacteriocins act on thebacterial cytoplasmic membrane itcan be hypothesized that the


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Bacteriocins and high

hydrostatic pressure (HHP)

Nisin in combination with HHPshowed strong synergistic effects

against L. plantarum, E. coli and L.monocytogenes.


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ADVANTAGES

an extended shelf life of foods.

provide extra protection duringtemperature abuse conditions.

decrease the risk for transmission offoodborne pathogens through thefood chain.

reduce the economic losses due tofood spoilage.

reduce the application of chemicalpreservatives.


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ADVANTAGES

Permit the application of less severeheat treatments withoutcompromising food safety: betterpreservation of food nutrients and

vitamins, as well as organolepticproperties of foods.

Permit the marketing of novel foods(less acidic, with a lower salt content,

and with a higher water content.they may serve to satisfy industrial

and consumers demands.


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Conclusions

A large number of bacteriocinsfrom LAB have been characterizedto date, and many differentstudies have indicated thepotential usefulness ofbacteriocins in food preservation.

Since the efficacy of bacteriocinsin foods is dictated byenvironmental factors, there is aneed to determine more preciselythe most effective conditions forapplication of each particular

bacteriocin


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Conclusions

The use of novel preservationtechnologies offers newopportunities for application ofbacteriocins as part of hurdletechnology, as has beendemonstrated for PEF and HHP.However, the combinedapplication of many other

technologies (such asultrasonication, irradiation,microwave and ohmic heating, orpulsed light) still remains

unexplored.


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References

Aasen, I.M., Markussen, S., Mretr, T.,Katla, T., Axelsson, L., Naterstad, K.,2003. Interactions of the bacteriocinssakacin P and nisin with food constituents.

International Journal of Food Microbiology87, 3543.

Abriouel, H., Valdivia, E., Glvez, A.,Maqueda, M., 1998. Response of

Salmonella choleraesuis LT2 spheroplastsand permeabilized cells to the bacteriocinAS-48. Applied and EnvironmentalMicrobiology 64, 46234626.

Abriouel, H., Maqueda, M., Glvez, A.,Martnez-Bueno M. Valdivia E. 2002.


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References

Gallo, L.I., Pilosof, A.M.R., Jagus, R.J.,2007. Effect of the sequence of nisin and

pulsed electric fields treatments andmechanisms involved in the inactivation of

Listeria innocua in whey. Journal of FoodEngineering 79, 188193.

Hauben, K.J.A., Wuytack, E.Y., Soontjens,C.C.F., Michiels, C.W., 1996. High

pressure transient sensitization ofEscherichia coli to lysozyme and nisin bydisruption of outer membrane permeability.Journal of Food Protection 59, 350355.

Szabo E A Cahill M E 1998 Thebi d ff t f difi d t h

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