Biomedical Engineering Reference
In-Depth Information
Staphylococcus aureus
) by enterocins has been reported in lettuce juices, soy milk,
and sport and energy drinks with lower acidity (Galvez et al.
2008
; Abriouel et al.
2010
). Since freshly-made fruit juices have been implicated in transmission of
enteric pathogens, bacteriocins (such as nisin and enterocin AS-48) have been tested
in combination with other agents to increase the bacterial outer membrane perme-
ability. The combined treatments of bacteriocins and PEF greatly increased the bac-
tericidal effects and decreased the risks of survivor proliferation in the treated
samples (Liang et al.
2002
; Mosqueda-Melgar et al.
2008
).
In fruit juices, the thermophilic endospore former
A. acidoterrestris
can with-
stand pasteurisation temperatures commonly applied during food processing, and
spoil freshly-made juices as well as processed juices. Even moderate growth of this
bacterium can confer an unpleasant medicinal taste to fruit juices, due to the pro-
duction of guaiacol. Some bacteriocins (mainly nisin and enterocin AS-48) have
been suggested as possible hurdles against this bacterium. Nisin (1.25-100 IU/ml)
was able to inhibit
A. acidoterrestris
in orange juice, grapefruit juice and apple juice
(Komitopoulou et al.
1999
) as well as in orange and fruit-mixed drinks (Yamazaki
et al.
2000
). Nisin was also able to inhibit spore germination at 25-50 IU/ml in
orange and mixed fruit drinks, but not by 600 IU/ml in clear apple juice, probably
because of a competitive effect of phenols (Yamazaki et al.
2000
). Addition of nisin
to orange juice (0, 50, 75, and 100 IU of nisin/ml juice) increased the thermal death
of
A. acidoterrestris
spores, with reported decrease in the D value up to 27 % heat
resistance as the nisin concentration was increased (Peña et al.
2009
). Enterocin
AS-48, added at low concentrations of 2.5
g/ml in fruit juices artifi cially contami-
nated with vegetative cells and endospores of
A. acidoterrestris
caused complete
bacterial inactivation and afforded protection for up to 14 days in freshly made
orange and apple juices and for up to 60-90 days in several commercial fruit juices
(Grande et al.
2005
). Electron microscopy examination of bacteriocin-treated veg-
etative cells revealed substantial cell damage and bacterial lysis. Treatment of endo-
spores with enterocin AS-48 caused inhibition of germination and disorganisation
of endospore structure.
Another heat-resistant bacterium in fruit juices is the non-sporeformer
Propionibacterium cyclohexanicum
, implicated in the spoilage of orange juice
(Kusano et al.
1997
). One study showed that addition of nisin (500 and 1,000 IU/ml)
to orange juice signifi cantly reduced the viable population of
P. cyclohexanicum
for
up to 15 days, but did not prevent regrowth of the bacterium during higher storage
periods (Walker and Phillips
2008
).
Fruit juices may also be spoiled by bacteria producing exopolysaccharides
(EPS), acrolein, or simply by growth causing turbidity. In apple juice and apple
ciders, added enterocin AS-48 (2.5-5
ʼ
g/ml) was very effective against EPS-
producing bacterial strains (including
B. licheniformis
LMG 19409,
Lactobacillus
collinoides
,
Lactobacillus diolivorans
and
Pediococcus parvulus
) as well as
3-hydroxypropionaldehyde -producing
L. collinoides
strains (Grande et al.
2006b
;
Martínez-Viedma et al.
2008a
). In coconut juice and coconut milk, addition of
enterocin AS-48 (at a fi nal concentration as low as 1.75
ʼ
g/ml) completely sup-
pressed
G. stearothermophilus
for at least 30 days of incubation at 45 °C (Martínez-
Viedma et al.
2009b
).
ʼ
