Agriculture Reference
In-Depth Information
(a)
4000
3000
2000
1000
0
(b)
20000
15000
10000
5000
0
(c)
10000
8000
6000
4000
2000
0
0
5
10
15
20
25
30
35
Days at 5 °C
Figure 13.6
Changes in total microbial counts (yeast and moulds, mesophilic aerobic micro-organisms,
mesophilic anaerobic micro-organisms) in
Opuntia
cactus stems (cladodes) held for up to 30 d at 5
°
C. (
●
):
without packaging, (
):
packaging in modified atmospheres. Vertical bars indicate standard error of the mean (From Guevara
et al
.
2001 with permission).
❍
): packaging in polyethylene bags with holes (high relative humidity), MAP (
▼
The application of passive or semi-active MA (CO
2
≤ 20%) to cladodes using RS425 Cryovac films increased
the shelf life even further to up to 35 days (Guevara
et al
.
2003). The oxygen concentration in passive MA packaging
decreased and reached about 8% after 35 days in storage,
while the CO
2
concentration increased to about 7.5% in the
same period of time.
In the semi-active MA, where 20% CO
2
is added to the
package, the oxygen level decreased to about 13%, and
the CO
2
level decreased to about 13.5% after 35 days in
storage. On the other hand, the CO
2
level in semi-active
MAP with an initial CO
2
level of 40% and 80%,
decreased to about 15 and 25%, respectively, and the
oxygen level slightly increased to about 15%, at the end
of the storage period (Guevara
et al
. 2003). The CO
2
lev-
els created in the semi-active MAP with initial of 40%
and 80% were higher than the minimum tolerated levels
for many fresh horticultural crops (Yahia 1998) and yet
did not appear to have a significant deleterious effect on
Opuntia
.
Firmness decreased in all cladodes, but the decrease was
faster in those that were kept in semi-active MAP with ini-
tial concentrations of 40% and 80% CO
2
, and cladodes that
were maintained without packaging, and the least firmness
loss was observed in the passive MAP and in semi-active
MAP with an initial 20% CO
2
(Figure 13.7, Guevara
et al
.
2003). The trends in changes in fibre content were similar
to those for firmness. The highest loss in fibre was observed
in cladodes maintained in semi-active MAP with initial
concentrations of 40% and 80% CO
2
, and in cladodes that
were maintained without packaging, and the lowest loss
was observed in the cladodes maintained in passive
MAP and in semi-active MAP with an initial concentration
of 20% CO
2
(Figure 13.7). It is possible that the loss in
