Agriculture Reference
In-Depth Information
0.18
(a)
(b)
0.12
0.16
0.14
0.10
0.12
0.08
0.10
0.08
0.06
0.06
0.04
0.04
0.00
0.00
0.030
0.04
(c)
(d)
0.025
0.03
0.020
0.015
0.02
0.010
0.01
0.005
0.000
0.00
0
10
20
30
40
0
10
20
30
40
Days at 5°C
Days at 5°C
Figure 13.9
Changes in chlorophyll content (total, a and b) and chlorophyllase activity in passive and
semi-active MA-packaged prickly pear cactus stems stored at 5
°
C for up to 35 days. Non packaged (●),
passive MAP (❍), 20% CO
2
(▼), 40% CO
2
(
∇
) and 80% CO
2
(■). Vertical bars represent standard error of the
mean (Guevara
et al
. 2003, with permission).
humidity in the atmosphere (Guevara
et al
. 2001; Yahia
et al
. 2005). On the other hand, elevated CO
2
levels (≥ 40%)
caused injury in cladodes in comparison with nonpackaged
cactus stems. There were no big differences in the quality
of prickly pear cactus stems packaged in passive MAP or
in semi-active MAP with an initial CO
2
concentration of
20%. The relative limit of tolerance of prickly pear cactus
stems to CO
2
is 20%. The storage life of the cactus stems
can be up to 32 days in passive MAP or in semi-active
MAP with an initial CO
2
concentration of 20%.
Several models have been used to describe the modified
atmosphere in packages of horticultural products; never-
theless, none of them integrate the effects of temperature
and the relative humidity as system variables. A model has
been generated and applied to describe the gas profile of
prickly pear cactus stems in passive and semi-active MAP
(Yahia
et al
. 2005; Guevara
et al
. 2006a, 2006b). The model
describes the gas exchange in nonsteady state, taking in
consideration the effect of temperature at 5°C, 14°C, 20°C
and 25°C and the relative humidity from 65-90% RH
(at intervals of 5 %) on film permeability characteristics,
respiration rate and tissue permeance of prickly pear cactus
stems. The model suitably describes the changes in CO
2
concentration and overestimates the O
2
concentration in
passive (no addition of gases) MAP of prickly pear cactus
stems. However, when a concentration of >20% CO
2
is
added to the packages, the model adequately describes
the changes in O
2
but sub-estimates the changes in CO
2
.
This might be due to high CO
2
concentration alterations in
tissue metabolism. The temperature and RH integration
and the small number of the measurable parameters in the
proposed model may help the model to be easily used for a
