Agriculture Reference
In-Depth Information
(a)
20
15
10
5
0
(b)
35
30
25
20
15
0
0
10
20
30
40
Days at 5°C
Figure 13.7
Changes in firmness (N) and crude fibre (%) in passive and semi-active MA-packaged prickly
pear cactus stems stored at 5
°
C for up to 35 days. Nonpackaged (●), 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).
firmness is caused by losses in fibre resulting in the
softening of the cladodes.
The retention in firmness of cladodes maintained in
passive MAP or in semi-active MAP with an initial con-
centration of 20% CO
2
might be due to the positive effects
of MA with intermediate CO
2
concentrations.
Weight loss was least in cladodes that were packaged in
passive MAP and in semi-active MAP with an initial con-
centration of 20% CO
2
, and the rest of the conditions
showed a high weight loss of more than 25% (Figure 13.8).
There was a close relation between weight loss and the
overall quality (Figure 13.8). Overall quality of the clad-
odes as judged subjectively was highest in cladodes that
were package in semi-active MAP with an initial 20% CO
2
,
followed by those packaged in passive MAP. Levels < 20%
CO
2
can decrease the rates of respiration and transpiration,
resulting in low weight loss. On the other hand, high CO
2
concentrations (over 20%) result in changes in cell perme-
ability and increased metabolic processes. Elevated CO
2
concentrations inactivate glycolytic and tricarboxylic
enzymes (malate dehydrogenase, succinic dehydrogenase
and cytochrome oxidase), generate an accumulation of
succinic acid, malate, acetaldehyde and ethanol, and reduce
cytochrome activity.
The decrease in chlorophyll content (total, a and b)
(Figure 13.9) during most of the storage period was the
least in cladodes that were maintained in passive MAP and
in semi-active MAP with an initial of 20% CO
2
, followed
by those packaged in semi-active MAP with initial concen-
trations of 40% and 80% CO
2
, and in those kept without
packaging (Guevara
et al
. 2003). Total chlorophyll and
chlorophyll a of cladodes kept in passive MAP and in
semi-active MAP with 20% CO
2
decreased about 23 and
35%, respectively, while elevated CO
2
concentrations
(40% and 80%) caused a decrease of about 53% and 63%,
respectively. Chlorophyll b content decreased about 57%,
58%, 37%, 80% and 99% in cladodes that were not
packaged, packaged in passive MAP, or packaged in semi-
active MAP with initial 20%, 40% or 80% CO
2
, respectively,
after 35 days in storage.
