Biomedical Engineering Reference
In-Depth Information
natural antimicrobials for food biopreservation. LAB may produce a wide variety of
active antagonistic metabolites such as organic acids (lactic, acetic, formic, propi-
onic, butyric, hydroxyl-phenyllactic acid, and phenyllactic acid), diverse antago-
nistic compounds (carbon dioxide, ethanol, hydrogen peroxide, fatty acids, acetoin,
diacetyl, reuterin, reutericyclin), antifungal compounds (propionate, phenyl-lactate,
hydroxyphenyl-lactate, cyclic dipeptides, phenyllactic acid and 3-hydroxy fatty
acids), and bacteriocins (such as nisin, pediocins, lacticins, enterocins and many
others) (Muhialdin et al.
2011
; Reis et al.
2012
; Oliveira et al.
2014
). Other bacterial
groups (especially those from genus
Bacillus
) are also attracting attention because
of the diversity of antimicrobial peptides they produce, some of which could also be
exploited as biopreservatives.
2.1.1
Antimicrobial Substances Derived from Bacterial
Cell Metabolism
Organic acids.
Fermentation is an oxido-reductive process in which organic acids
are the main end products. Lactic acid is the main organic acid produced during
fermentation. Organic acids decrease the pH of the surrounding environment, creat-
ing a selective barrier against non-acidophiles. In addition, organic acids also have
antibacterial activity. The antimicrobial effect of lactic acid is exerted by disruption
of the cytoplasmic membrane and interference with membrane potential (Axe and
Bailey
1995
) and/or reduction in intracellular pH (Shelef
1994
).
CO
2
.
Heterofermentative LAB produce CO
2
as a byproduct of sugar fermenta-
tion. The production of CO
2
creates an anaerobic environment has antagonistic
effects specifi cally against aerobic bacteria (Adams and Nicolaides
1997
). It also
dissolves in water, generating carbonic acid.
Diacetyl.
Certain LAB may produce diacetyl (2,3-butanedione) is a by-product
of the metabolic activity (Jay
1982
). Diacetyl exhibits antibacterial activity against
Listeria, Salmonella, Escherichia coli, Yersinia,
and
Aeromonas
(Jay
1982
). Gram-
negative bacteria are generally more sensitive than gram-positive bacteria to diace-
tyl (Adams and Nicolaides
1997
)
.
However, since the high concentrations of
diacetyl required to achieve inhibition of spoilage bacteria also affect the sensory
properties of the food (Helander et al.
1997
), the use of diacetyl-producing cultures
for protective purposes should be limited to foods where diacetyl is an essential
component of the food sensory properties (Jay
1982
).
Hydrogen peroxide.
LAB are defi cient in catalase activity. Hydrogen peroxide is
produced in the presence of oxygen as a result of the action of fl avoprotein oxidases
or NADH peroxidase (Ammor et al.
2006
)
.
Hydrogen peroxide is thought to elicit
an antibacterial effect through oxidative damage of proteins, but it also may increase
membrane permeability (Kong and Davison
1980
).
Reuterin.
Also known as 3-hydroxypropionaldehyde (3-HPA), reuterin is a low-
molecular-weight antimicrobial compound produced by
Lactobacillus reuteri
