Agriculture Reference
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Jacxsens et al (
2002b
) also investigated packaged minimally processed mixed
lettuce under various temperatures (from 5 to 20 °C) in a simulated cold distribution
chain, typical of commercial practice, on the microbial quality of EMA (3 % O
2
and
5 % CO
2
). The internal atmosphere in the packages remained in its aerobic range
during storage in the chain. However, yeasts were shown to be the shelf life limiting
group (day 4). Finally, color limited sensorial shelf life down to 5 days.
Jacxsens et al. (
2003
) attempted to evaluate the quality of mixed lettuce (mixture
of endive, curled endive, radicchio lettuce,
lollo rosso
and
lollo bionta
lettuces) with
an initial atmosphere of 3 % O
2
and 2-5 % CO
2
and two types of fi lms (low and high
permeability). Lettuce stored under EMA (equilibrium modifi ed atmosphere) (high
permeability fi lm) had a shelf life of 6 days (limited by growth of psychrotrophs and
yeasts) whereas anaerobic conditions in packages of low permeability fi lm resulted
in limited shelf life up to 3 days (due to ethanol production release).
Salmonella enteritidis
and
L. monocytogenes
was inoculated to fresh lettuce that
was afterwards stored under MAP with initial head-spaces of 4.9 % CO
2
/2.1 %
O
2
/93 % N
2
and 5 % CO
2
/5.2 % O
2
/89.8 % N
2
, respectively. Total aerobic counts and
lactic acid bacteria (LAB) were lower (0.4 and 0.5 log CFU/g, respectively) in the
treated samples. However, both studied pathogens survived but showed no growth
regardless of the packaging system applied (Kakiomenou et al.
1998
).
Romaine lettuce leaves were sliced, washed, dried and packaged in fi lms with
oxygen transmission rates (OTR) of 8.0 and 16.6 pmol s
−1
m
−2
Pa
−1
, and with initial
O
2
headspace of 0, 1, 2.5, 10 and 21 kPa and stored at 5 °C. Ethanol accumulation
in 16.6 OTR packages was less than half of that in 8.0 OTR packages fl ushed with
≤
10 kPa O
2
. For both package types, the onset and the intensity of off-odors was
further delayed when fl ushed with 21 kPa O
2
than fl ushing with <10 kPa O
2
. Samples
fl ushed with 0 or 1 kPa O
2
displayed higher electrolyte leakage than those fl ushed
with higher concentrations of O
2
(Kim et al.
2005
).
Romaine lettuce was stored under passive MAP (an LDPE and a medium density
PE fi lm was used) under 0 or 5 °C for a storage period of 14 days. Ascorbic acid was
better preserved in LDPE packages at 0 °C (81.1 and 77.5 mg/100 g at 0 and 5 °C,
respectively). The best visual quality was recorded for samples stored in LDPE bags
at 0 °C (Manolopoulou et al.
2010
).
The impact of cutting method and packaging fi lm [BOPP and a polyolefi n (PO)]
on sensory quality of butterhead lettuce stored at 5 °C was studied by Martinez et al.
(
2008
). In comparison with the fresh sample, dark stains signifi cantly developed on
the 8th storage day for the lettuce stored in the BOPP fi lm and cut manually with a
knife, on the 10th day for the lettuce stored both in the BOPP and PD-961 fi lms
when cut, and on the 17th day in the PD-961 fi lm and cut manually.
Winter harvested iceberg lettuce was vacuum-cooled and stored under PMAP
(perforated PP, PP 25, 30 and 40
m) and AMAP (5 % O
2
and 0 % CO
2
), while
brown stain and heart leaf injury were only detected on heads packaged in unperfo-
rated bags. The best treatments for ensuring visual quality were the passive MAP in
40 mm PP and A MAP in 30 mm PP. Pink rib and heart-leaf injury were both
reduced by vacuum cooling but the effect only showed up during their shelf-life
period (Martinez and Artes
1999
).
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