Biomedical Engineering Reference
In-Depth Information
Addition of nisin in deli-type salads reduced the concentrations of viable
Listeria
following bacteriocin treatment, but it did not prevent overgrowth of survivors dur-
ing storage (Schillinger et al.
2001
). In vegetable salads (containing a mayonnaise-
blended mixture of ingredients such as boiled potato, carrots, peas, olives, egg and
tuna) complete inactivation of
L. monocytogenes
population was achieved by add-
ing enterocin AS-48 at 60
g/g in combinations with a variety
of antimicrobial substances such as essential oils or their bioactive compounds,
and chemical preservatives (Cobo Molinos et al.
2009a
). Synergistic effects were
also reported in salads against a cocktail of
S. enterica
serovars for AS-48 and
p
- hydroxybenzoic acid methyl esther or 2-nitropropanol (Cobo Molinos et al.
2009b
). In vegetable sauces, inactivation of
S. aureus
improved considerably when
combinations of enterocin AS-48 and hydrocinnamic acid or carvacrol were added
(Grande et al.
2007a
).
In cooked vegetable foods, most vegetative cells can be inactivated during the
heat processing. However, endospores surviving heat treatments can proliferate in
the fi nished product unless additional hurdles (such as bacteriocins) are included.
Enterocin AS-48 added in a concentration range of 20-35
ʼ
g/g singly or at 30
ʼ
g/g to boiled rice and in
a commercial infant rice-based gruel dissolved in whole milk and inoculated with
vegetative cells and endospores of
B. cereus
, completely suppressed the bacilli dur-
ing storage in a temperature range of 6-37 °C for up to 15 days and prevented
enterotoxin production (Grande et al.
2006b
). Bacteriocin activity was improved by
adding sodium lactate, decreasing the bacteriocin concentration to 8-16
ʼ
g/g with-
out compromising inactivation of the bacilli. Application of AS-48 in combination
with heat treatments decreased the thermal death
D
values for endospores (Grande
et al.
2006b
). In desserts and bakery ingredients, the effi cacy of AS-48 (added in a
concentration range of 5-50
ʼ
g/g) against
S. aureus
,
B. cereus
, and
L. monocyto-
genes
depended to a great extent on the food substrate and the target bacteria
(Martínez-Viedma et al.
2009a
,
b
,
c
). Bacteriocin activity in chocolate cream
increased markedly when tested in combination with eugenol, 2-nitropropanol or
Nisaplin (Martínez-Viedma et al.
2009c
).
L. monocytogenes
has been reported to grow on tofu stored at refrigeration
temperatures (Schillinger et al.
2001
). Nisin showed limited effi cacy against
L. monocytogenes
Scott A in tofu. Following an initial reduction of viable counts by
nisin, regrowth of survivors was observed during further incubation (Schillinger
et al.
2001
). To improve microbial inactivation, nisin was tested in combination with
bacteriocinogenic strains
Enterococcus faecium
BFE 900-6a or
L. lactis
BFE 902 as
protective cultures, resulting in a complete suppression of listerial growth in home-
made tofu stored at 10 °C for 1 week (Schillinger et al.
2001
).
Canning and cooking processes of vegetables destroy most of the vegetative bac-
terial forms. Yet, due to the high thermal resistance of endospores and the frequent
endospore contamination of raw materials, endospore-forming bacteria represent
the main risk for spoilage of foods prepared in this way. Additional hurdles such as
refrigeration, acidifi cation, addition of salt or chemical preservatives are often
required to avoid proliferation of sporeformers in the processed products. Several
studies support the practical application of bacteriocins in this category of
ʼ
