Agriculture Reference
In-Depth Information
Francis and O'Beirne (
1997
) studied the effect of temperature, antimicrobial
dips (100 ppm chlorine solution or 1 % citric acid solution for 5 min) and gas atmo-
sphere (initial gas fl ush with 100 % N
2
or passive MAP) on
L. innocua
and
L. mono-
cytogenes
inoculated on iceberg lettuce. Nitrogen fl ushing favored the
Listeria
growth more than in unfl ushed packages while the use of antimicrobial dips led to
better survival of
L. innocua
at 3 °C.
Francis and O'Beirne (
2001
) investigated shredded iceberg lettuce during stor-
age at 4 and 8 °C and under PMAP in regard to the survival and growth of inocu-
lated
L. monocytogenes
and
E. coli O157
:
H7
[oriented PP (OPP) fi lm used].
L.
monocytogenes
populations rose by approximately 1.5 log cycles during the 12-day
storage period at 8 °C, whereas fi nal population densities of
E. coli O157
:
H7
varied
in the range 6.5-7.0 log CFU/g.
Gleeson and O'Beirne (
2005
) analyzed the effects of different slicing methods
during storage (8 °C) on subsequent growth and survival of inoculated
L. innocua
and
E. coli
on passive MAP (PMAP) preserved vegetables (sliced iceberg and but-
terhead lettuce). The slicing instrument is of great importance since slicing with a
blunt knife resulted in consistently higher
E. coli
and
L. innocua
counts during stor-
age than slicing with a razor blade (1.2 log CFU/g lower for
L. innocua
and 0.6 log
CFU/g for
E. coli
on butterhead lettuce).
Gomez-Lopez et al (
2005
) focused on the impact of intense light pulses decon-
tamination on the shelf-life of minimally processed lettuce stored at 7 °C in equilib-
rium MAP (fi lms with OTR: 2,290 mL/kg h). Five days of experimentation made
evident that the psychrotrophic count of treated samples was kept lower (0.46 log
CFU/g reduction) than that for the controls whilst yeasts counts amount to 1.8 log
CFU/g at day 5 for treated lettuce were higher, but still at low levels.
Iceberg lettuce was treated with gaseous chlorine oxide and cysteine (0.5 % solu-
tion) and stored under MAP at 7 °C (initial atmosphere of 2-4 % O
2
and 9 % CO
2
)
conditions. Microorganisms (mesophiles and psychrotrophs) surviving decontami-
nation grew more rapidly than those present in non-decontaminated samples, as
reported by Gomez-Lopez et al. (
2008
). Therefore, decontamination can consider-
ably accelerate the spoilage rate.
Fresh-cut lettuce, washed with chlorinated water and stored under PMAP (poly-
olefi n laminated fi lm used) was irradiated at a mean dosage of 0.19 kGy. The result-
ing product had, 8 days after irradiation, microbial population of 290 CFU/g and
yeast population of 60 CFU/g, compared with values of 220,000 and 1,400 CFU/g,
respectively, for the non-irradiated control. Lettuce irradiated at 0.81 kGy required
a mean force of 1,236 N compared to 1,311 N for control (Hagenmaier and Baker
1997
).
Jacxsens et al (
2002a
) used active atmosphere modifi cation (AAM) (3 % O
2
and
5 % CO
2
) in order to assess temperature dependence of shelf life of mixed lettuce
(mixture of 20 % endive, 20 % curled endive, 20 % radicchio lettuce, 20 %
lollo
rosso
and 20 %
lollo bionta
lettuces) as affected by microbial proliferation. The
result of the temperature rise was a decrease of the lag-phase of spoilage micro-
organisms (105 h reduction from 2 to 4 °C). Lettuce retained its organoleptic char-
acteristics best at a storage temperature of 4 °C.
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