brated, using distilled water, for measurement at 20°C. Titratable acidity was measured on each
fruit from an accurately weighed sample of de- canted juice free of pulp residue usually a volume
of 1 – 5 ml diluted to 40 ml using distilled water. Each sample was titrated against 0.1 M sodium
hydroxide to pH 8.2 using a Mettler DL20 com- pact titrator. Results were expressed as percentage
anhydrous citric acid. The two major diseases were anthracnose Colletotrichum gloeosporioides
Penz. Penz. and Sacc. and stem end rot Doth- iorella dominicana Petrak and Cif., Lasiodiplodia
theobromae Griff. and Maubl.. The severity of disease was assessed 4 days after treatment ac-
cording to the percentage skin area affected by either one or both diseases per fruit, and then the
percentage scores were related to a 5-point scale where 0 = 0 skin area affected; 1 = 1 – 5; 2
mild = 6 – 15; 3 moderate = 16 – 30; and 4 severe = 31 – 100 skin area affected.
Data were examined by analysis of variance using the QDPI BALF.9106 software package.
The analysis examined the effect of conditioning treatment, with variation between fruit within
treatments being used as the error term. Graphs of variables against conditioning temperature
were assessed before deciding whether it would be useful to partition the temperature portion of the
treatment effect into polynomial components. However, these graphs did not indicate any useful
relationships. Instead pairwise comparisons be- tween means were made using the protected least
significant difference procedure. All testing was carried out at P = 0.05.
3. Results
3
.
1
. Experiment
1:
optimum temperature for
8
h to generate heat tolerance
The average internal pulp colour rating of fruit was 4 and total solids level 15.3 9 0.24, indi-
cating that fruit were commercially mature. There were no differences in weight loss between fruit
conditioned at the different temperatures, but un- treated fruit 1.7 lost significantly less weight
than treated fruit from 2.17 to 2.29 Table 1. Skin colour, reflectance, chroma and hue angle
values before or after HWT data not shown did not differ. Conditioning treatments, except for
30°C, decreased fruit firmness by 25 – 40 com- pared to untreated fruit 19.1 N 4 days after
HWT Table 1. Fruit conditioned at 30°C 21.7 N were the firmest, followed by untreated fruit
19.1 N. There were no significant differences from the other conditioning treatments.
Untreated fruit Tables 2 and 3 had no exter- nal or internal injuries, and there were no external
injuries on any fruit for 24 h after HWT data not shown. Fruit conditioned at 38 – 42°C did not
show skin scalding. However, fruit conditioned at 30°C before being heated to 47°C core tempera-
ture for 15 min had the highest incidence and severity of skin scalding followed by fruit condi-
tioned at 22°C Tables 2 and 3. Cavitation only occurred in fruit from these two treatments Table
2. All conditioned fruit displayed lenticel spotting 4 days after HWT, that decreased with increasing
conditioning temperature, especially above 40°C Tables 2 and 3. Fruit conditioned at 40 and
42°C had the lowest incidences and severities of lenticel spotting.
Table 1 Weight loss and firmness of ‘Kensington’ fruit either given an
8 h conditioning treatment and then a HWT 47°C fruit core temperature held for 15 min before storage at 22°C, or placed
directly at 22°C after harvest untreated
a
Fruit firmnessN Weight loss
Treatment
b
19.12
ab
1.69
b
Untreated 2.26
a
14.20
bc
22°C for 8 h+HWT
2.17
a
30°C for 8 21.70
a
h+HWT 14.26
bc
2.24
a
38°C for 8 h+HWT
12.79
c
40°C for 8 2.29
a
h+HWT 11.43
c
42°C for 8 2.20
a
h+HWT SEM
c
1.89 0.09
a
Means within a column not followed by a bold superscript common letter are significantly different PB0.05.
b
All measurements were made after 4 days of storage at 22°C; values presented are the means of 14 fruit.
c
Standard error of mean.
Table 2 The incidence of external and internal injuries of ‘Kensington’ fruit either given an 8 h conditioning treatment and then a HWT
47°C fruit core temperature held for 15 min before storage at 22°C, or placed directly at 22°C after harvest untreated
a
Treatment External
External External
Internal Internal
External cavities Lenticel spotting
Starch layer Skin scalding
Starch layer Untreated
12.5 100
50 50
22°C for 8 h+HWT 62.5
62.5 30°C for 8 h+HWT
12.5 100
75 87.5
38°C for 8 h+HWT 100
12.5 87.5
40°C for 8 h+HWT 62.5
25 42°C for 8 h+HWT
a
All measurements were made after 4 days of storage at 22°C; values presented are the percentages of fruit showing injury from a total of eight fruit.
Fruit conditioned at 38 – 42°C did not have starch layers Tables 2 and 3, while fruit condi-
tioned at 30°C prior to HWT had the highest incidence and severity, followed by fruit condi-
tioned at 22°C. Fruit conditioned at 40°C prior to HWT were the only heated fruit not to possess
starch spots Tables 2 and 3.
3
.
2
. Experiment
2:
increased heat tolerance deri6ed from conditioning treatments
The average internal pulp colour rating for fruit was 4 and total solids level 15.7 9 0.31, indi-
cating that fruit were commercially mature. Un- treated fruit had significantly lower weight loss
2.8 than the other treatments and there were no significant differences in weight loss between
fruit conditioned at the different temperatures Table 4. There were no significant differences
between treatments in skin colour rating, reflec- tance brightness, chroma colour intensity and
hue angle skin yellowness before and 4 days after treatment data not shown. Four days after
transfer to 22°C, the untreated fruit were firmer, but not significantly firmer than fruit conditioned
at 22, 30, or 38°C Table 4. There was a trend towards increased fruit softness with higher condi-
tioning temperature 30 – 42°C. Fruit conditioned at 42°C prior to HWT and then stored at 22°C
for 4 days had the highest brix levels 14.44°, but this was not significantly different from untreated
fruit or fruit conditioned at 38 – 42°C Table 4. Titratable acidity tended to decrease with increas-
ing conditioning temperature Table 4. Untreated fruit did not exhibit any skin scald-
ing or cavitation, but had a high incidence of lenticel spotting Tables 5 and 6. The incidence of
skin scalding was severe for fruit conditioned at 22 and 30°C, followed by fruit conditioned at 40,
38 and 42°C Tables 5 and 6. The optimum temperature for the reduction of skin scalding was
42°C Tables 5 and 6. All conditioned fruit had some incidence of external cavitation. The fruit
conditioned at 30°C had the highest incidence of cavitation, followed by the fruit conditioned at 38
and 42°C. Fruit conditioned at 40 and 22°C had the lowest incidence of cavitation. All fruit condi-
tioned prior to HWT had a significantly higher severity of lenticel spotting compared with the
untreated fruit Table 6. Untreated fruit had no internal injuries Tables 5 and 7. Fruit condi-
tioned at 40°C had the least and fruit conditioned at 22 and 30°C the highest starch layer injury
Table 7. Fruit conditioned at 38 and 40°C had no starch spot injury, while 100 of fruit condi-
tioned at 22 and 30°C and 10 of fruit condi- tioned at 42°C had starch spots Tables 5 and 7.
Fruit conditioned at 22 and 30°C had the highest disease severity Table 6. Fruit in all other treat-
ments displayed either no disease or had ex- tremely low disease severity.
4. Discussion
