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E. coli
inoculated.
PMAP 1
PMAP 2
PMAP 3
PMAP 4
PMAP 5
PMAP 6
PMAP 7
PMAP 8
9
8
158C
88C
7
158C
6
5
48C
48C
48C
88C
4
88C
3
0
2
4
6
8
10
12
14
Storage Time (Days)
Fig. 1.2
E. coli
colonies inoculated on lettuce and stored under modifi ed atmospheres. [PMAP 1
(with steady-state atmosphere of 3-4 % O
2
/10-12 % CO
2
), for iceberg lettuce, PMAP 2 (with
steady-state atmosphere of 3-4 % O
2
/10-12 % CO
2
) for iceberg lettuce, Francis and O'Beirne
(
2001
), PMAP 3 (with oriented polypropylene as a packaging fi lm) and inoculation with
E. Coli
and
L. innocua
for razor blade cut iceberg lettuce, PMAP 4 (with oriented polypropylene as a
packaging fi lm) and inoculation with
E. coli
and
L. innocua
for razor blade cut butterhead lettuce,
Gleeson and O'Beirne (
2005
), PMAP 5 and PMAP 6 (2 % O
2
-98 % N
2
and a fi lm with OTR:
110 mL/m
2
cm
3
day) and inoculation with
E. coli O157
:
H7
strains and PMAP 7 and PMAP 8 (fi lm
with OTR: 110 mL/m
2
cm
3
day and with 40 microperforations) and inoculation with
E. coli
O157
:
H7
strains (Sharma et al.
2011
) ]
growth of inoculated
E. coli
, limiting its population down to acceptable levels, as
can be seen in Fig.
1.2
.
An investigation was also carried out on the effect of different O
2
levels from 0
to 100 kPa in conjunction with 0, 10 and 20 kPa CO
2
on the respiration metabolism
of greenhouse grown fresh-cut butter lettuce. The concluding remark is that 80 kPa
O
2
(superatmospheric conditions) must be used in MAP to prevent fermentation of
lettuce when combined with 10-20 kPa CO
2
for the reduction of their respiration
rate (Escalona et al.
2006
).
Fan and Sokorai (
2011
) investigated the effect of different irradiation doses (0.5
and 1 kGy) on quality of iceberg lettuce stored under MAP (nitrogen gas fl ush and
storage in bags with 6,000-8,000 mL/m
2
/day OTR) at 4 °C for 14 days. The irradi-
ated samples stored under MAP maintained quality over the limit of sales appeal
(the limit was set to 5), while those stored at air showed extended tissue browning
and quality degradation (Table
1.2
).
Treatment with warm water (dipping in water for 2 min in either 5 or 47 °C)
before irradiation (0, 0.5, 1 or 2 kGy) of iceberg lettuce and packaging under passive
MAP (fi lms with OTR: 4,000 mL/h m
2
) at 3 °C was studied by Fan et al. (
2003
).
Less tissue browning was reported for lettuce dipped at 47 °C and irradiated at 0.5
and 1 kGy in comparison to corresponding irradiated samples dipped at
5 °C. Irradiated lettuce had better overall physical and sensory properties than non-
irradiated lettuce dipped at either 47 or 5 °C. Application of irradiation induced
higher antioxidant content which was nulled by the 47 °C water dip effect.
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