05-09-2012, 10:08 AM
Bacteriocins from Lactic Acid Bacteria: Purification, Properties and use as Biopreservatives
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ABSTRACT
Biopreservation systems in foods are of increasing interest for industry and consumers. Bacteriocinogenic lactic
acid bacteria and/or their isolated bacteriocins are considered safe additives (GRAS), useful to control the
frequent development of pathogens and spoiling microorganisms in foods and feed. The spreading of bacterial
antibiotic resistance and the demand for products with fewer chemicals create the necessity of exploring new
alternatives, in order to reduce the abusive use of therapeutic antibiotics. In this context, bacteriocins are
indicated to prevent the growth of undesirable bacteria in a food-grade and more natural way, which is
convenient for health and accepted by the community. According to their properties, structure, molecular weight
(MW), and antimicrobial spectrum, bacteriocins are classified in three different groups: lantibiotics and nonlantibiotics
of low MW, and those of higher MW. Several strategies for isolation and purification of bacteriocins
from complex cultivation broths to final products were described. Biotechnological procedures including saltingout,
solvent extraction, ultrafiltration, adsorption-desortion, ion-exchange, and size exclusion chromatography
are among the most usual methods. Peptide structure-function studies of bacteriocins and bacterial genetic
advances will help to understand the molecular basis of their specificity and mode of action.
INTRODUCTION
One of the concerns in food industry is the
contamination by pathogens, which are frequent
cause of food borne diseases. Over the past
decade, recurrent outbreaks of diarrhea, combined
with the natural resistance of the causative agents,
contributed to its status as hazard.
The problem of selection of resistant bacteria to
antibiotics (Parada, 1980; Chopra et al, 1997; Rao,
1998; Kapil, 2005) and the increasing demand for
safe foods, with less chemical additives, has
increased the interest in replacing these
compounds by natural products, which do not
injure the host or the environment. Biotechnology
in the food-processing sector targets the selection,
production and improvement of useful
microorganisms and their products, as well as their
technical application in food quality.
Lactic Acid Bacteria
Lactic acid bacteria (LAB) are characterized as
Gram-positive cocci or rods, non-aerobic but
aerotolerant, able to ferment carbohydrates for
energy and lactic acid production. The metabolic
pathway from glucose may be homofermentative
or heterofermentative. In the first case two
molecules of lactate are generated (as in
Streptococcus and Lactococcus), and in the
second, lactate, ethanol and carbon dioxide are
produced, as in Leuconostoc and some lactobacilli.
Lactic acid bacteria are also able to produce small
organic substances that contribute with aroma and
give specific organoleptic attributes to the
products (Caplice and Fitzgerald, 1999).
Bacteriocin-like Substances
Lactic acid bacteria are capable of producing other
substances, known as bacteriocin-like substances
(BLS). An example of this class of molecule is
reuterin, produced by some strains of
Lactobacillus reuteri during anaerobic
fermentation of glycerol (Rodríguez et al, 2003;
Pancheniak et al, 2006). It is water-soluble, active
over a wide range of pH values and resistant to
proteolytic and lipolytic enzymes, being a suitable
compound for food biopreservation.
Lactobacillus plantarum TF711 isolated from raw
Tenerife goat’s cheese dy Hernández et al (2005)
produced a bacteriocin-like substance with a
molecular weight of 2,5 kDa, which was called
plantaricin TF711. It was shown to be active
against the Gram-positive bacteria Bacillus cereus,
Clostridium sporogenes and Staphylococcus
aureus, as well as against the Enterobacteriaceae
Shigella sonnei and Klebsiella pneumoniae.
Isolation and Purification
The first step for isolation of bacteriocins involves
a screening of lactic acid bacteria from different
sources, which may vary from plant material and
food products to human or animal isolates.
Moreno et al (1999) have isolated several strains
of lactic acid bacteria from food products as
cheese and milk. The antagonistic activity was
detected through the well diffusion assay on agar
plates (Toro, 2005). To avoid antagonism by
hydrogen peroxide, catalase was added to the
culture medium; phosphate buffer was added to
the solid medium to exclude inhibition by organic
acids. Additional tests in liquid medium are
confirmatory and allow the determination of
minimal inhibitory concentration.
Perspectives
Lactic acid bacteria have been recognized as safe,
and bacteriocins produced by these
microorganisms may be a good solution to the
problem of resurgence of resistant strains to
antibiotics.
During the last decade, a large number of LABbacteriocins
have been identified, and in some
cases, biochemically and genetically characterized.
This explosion in bacteriocin research has been
favored by the recognition of the role that these
producing bacteria may play in the hygienicquality
assurance of food and as feed supplements
(Pancheniak, 2005; Toro, 2005). However, to date
only few bacteriocins are used as biopreservatives.
This may be partially due to the fact that newly
discovered broad-spectrum bacteriocins have yet
to be fully characterized and officially approved.