3. Results
3
.
1
. Effect of heat-conditioning treatments on chilling injury and catalase acti6ity of
‘
Fortune
’
mandarins Chilling symptoms appeared by 2 weeks at 2°C
storage in the non-conditioned ‘Fortune’ fruits Fig. 1A. The CI index of these fruits increased
continuously for up to 4 weeks. The susceptibility of the ‘Fortune’ mandarins decreased consider-
ably in HAT fruit. The CI index of fruits exposed to this treatment was about 0.3 after 4 weeks
storage, whereas that of the non-conditioned fruit was 1.8. Dipping the fruits for 3 min at 53°C also
increased the tolerance of ‘Fortune’ mandarins to chilling, although this treatment was less effective.
The dip treatment delayed cold-induced peel dam- age but chilling symptoms were apparent by 3
weeks at 2°C. After 4 weeks storage, the CI index of dipped fruits was about 61 that of non-condi-
tioned fruits.
CAT activity in the flavedo of ‘Fortune’ man- darins quickly increased after the HWD treatment
at 53°C but this increase was lower than that induced by heating the fruits for 3 days at 37°C
Fig. 1B. In general, the decline in CAT activity in heat-conditioned and in non-conditioned fruits
after cold storage followed a different pattern. After 3 weeks, fruit dipped for 3 min at 53°C
showed similar CAT activity to that of non-condi- tioned fruits. However, in the 3-day conditioned
fruits the activity of the enzyme remained consid- erably higher than in non-conditioned fruits
throughout the 4 weeks of exposure to low temperature.
3
.
2
. Effect of AT on heat-induced tolerance to cold stress and on the acti6ity of the enzymes of
the antioxidant system in
‘
Fortune
’
mandarins The effectiveness of the HAT increasing chilling
tolerance of ‘Fortune’ mandarins was reduced when CAT activity was inhibited by AT. After 1
week of storage at 2°C the CI index of these fruits was even higher than that of the non-treated
fruits, which showed slight peel damage after 14 days at 2°C Sala and Lafuente, 1999. Peel dam-
age was, however, negligible in conditioned fruits treated with AT for up to 8 weeks storage at a
non-chilling temperature 12°C; Fig. 2.
AT treatment barely affected the activities of APX, GR and SOD in this citrus cultivar Fig.
3B, C and D. However, the activity of the en- zyme CAT was reduced to about 25 – 33 by AT
over the storage period studied in the HAT fruit Fig. 3A. The CAT activity in the HAT fruits
treated with AT ranged from 8.1 to 6.5 units mg protein
− 1
Fig. 3A after 2 weeks storage at 2°C;
Fig. 1. Effect of a hot-water dip treatment at 53°C for 3 min and a 3-day heat-conditioning treatment at 37°C and 90 – 95
RH on CI index A and CAT activity B of ‘Fortune’ mandarins stored for up to 4 weeks at 2°C. Each value is the
mean of three replicate samples 9 S.E.
Fig. 2. CI index of ‘Fortune’ mandarin fruits treated with AT and conditioned for 3 days at 37°C and 90 – 95 RH and stored
for up to 8 weeks at 2°C. Fruits stored at 2°C
and 12°C . Values are the mean of three replicate samples 9 S.E.
Fig. 3. Effect of AT on CAT, APX, GR and SOD of ‘Fortune’ mandarin fruits conditioned for 3 days at 37°C and stored for
up to 8 weeks at 2°C. Data are expressed as relative activity histograms calculated as the ratio of the activity of the enzymes
in the flavedo of the AT-treated fruits with respect to the non-treated ones and as absolute enzyme activity closed
circle in fruits treated with AT. Each value is the mean of three replicate samples 9 S.E.
whereas it ranged between 33.1 and 19.9 units mg protein
− 1
in the non-AT treated fruits Sala and Lafuente, 1999.
3
.
3
. Effect of AT on peel damage and on the acti6ity of the enzymes of the antioxidant system
in
‘
Clementine
’
and
‘
Clemenules
’
mandarins The fruits of ‘Clementine’ and ‘Clemenules’ cul-
tivars were chilling-tolerant. These cultivars did not show peel damage for up to 8 weeks at 2°C
but peel damage appeared after 2 weeks storage at 2°C when fruits were treated with AT Fig. 4. No
peel damage occurred during storage of the AT- treated and the non-treated fruits at 12°C data
not shown.
The effect of AT treatment on the pattern of changes in the activities of the enzymes of the
antioxidative system in non-conditioned ‘Clemen- tine’ and ‘Clemenules’ fruits is shown in Fig. 5. In
both cultivars, the activity of CAT was reduced to about the 40 – 50 and remained lower in AT-
treated fruits during storage at low temperature Fig. 5A, B. The activities of APX Fig. 5C,
Fig. 4. Peel damage of ‘Clementine’ and ‘Clemenules’ man- darin fruits stored for up to 6 weeks at 2°C. The extent of
injury was evaluated in fruits non-treated
and treated with AT
. Values are the mean of three replicate samples 9 S.E.
Fig. 5. Effect of AT on CAT, APX, GR and SOD activity of ‘Clementine’ A, C, E and G and ‘Clemenules’ B, D, F and
H mandarin fruits non-treated
and treated b with AT and stored for up to 6 weeks at 2°C. Each value is the mean
of three replicate samples 9 S.E.
D, GR Fig. 5E, F and SOD Fig. 5G, H showed, in general, little change when the fruits
were treated with AT.
4. Discussion
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