Postharvest Biology and Technology 21 2000 39 – 49
Effects of hot air conditioning of ‘Kensington’ mango fruit on the response to hot water treatment
Keryl K. Jacobi
a,
, Elspeth A. MacRae
b
, Suzan E. Hetherington
c
a
Queensland Horticulture Institute, Gatton Research Station, Locked Mail Bag
7
MS
437
, Gatton,
4343
. Queensland, Australia
b
Posthar6est Science Group, HortResearch, Mt Albert Research Centre, Pri6ate Bag
92 169
, Auckland, New Zealand
c
School of Land and Food, The Uni6ersity of Queensland, St Lucia,
4072
. Queensland, Australia Received 6 March 2000; accepted 19 August 2000
Abstract
Hot air conditioning treatments of mature ‘Kensington’ mango fruit Mangifera indica Linn. were optimised by incubating fruit at temperatures from 22 to 42°C for 4 – 16 h, prior to a hot water treatment HWT of 45°C for 30
min or 47°C for 15 min, before ripening at 22°C. Hot water injuries were reduced, and in some cases, eliminated, by conditioning the fruit at 40°C for 8 h. The conditioning temperature was more important than the duration of the
HWT in injury alleviation. Conditioning at 40°C prior to HWT accelerated the ripening of fruit, increased weight loss, reduced fruit firmness, increased brix and lowered titratable acidity compared to untreated fruit and fruit
receiving other heat treatments. These treated fruit were also more resistant to postharvest diseases. © 2000 Elsevier Science B.V. All rights reserved.
Keywords
:
Heat treatments; Thermotolerance; Mango; Mangifera indica; Postharvest storage; Fruit; Ripening www.elsevier.comlocatepostharvbio
1. Introduction
Conditioning ‘Kensington’ mango fruit at 40°C increases heat tolerance through a reduction or
elimination of heat injuries Jacobi et al., 1995, 1996. Previously, Joyce and Shorter 1994 had
demonstrated that the severity of cavitation and retention of starchy regions within heat-damaged
mesocarp of ‘Kensington’ fruit, could be reduced by a slow 7-h heating of the fruit to a 37°C core
temperature. These authors maintained fruit at 37°C for 5 12 h prior to a HWT of 47°C core
temperature held for 25 min. For avocado Woolf et al., 1995 and tomato Hakim et al., 1996
temperatures in the range 25 – 46°C applied for 0.5 – 72 h have also proved effective in raising fruit
heat tolerance.
In previous research reported by Jacobi et al. 1996, injuries to fruit not conditioned before
HWT, included accentuated lenticel spotting, ex- ternal and internal cavities and starchy layers
beneath the skin. A conditioning treatment of 40°C for 8 – 12 h was found to minimise these heat
injuries to the fruit. This paper reports on the
Corresponding author. Tel.: + 61-7-54623223; fax: + 61- 7-54623223.
E-mail address
:
jacobikdpi.qld.gov.au K.K. Jacobi. 0925-521400 - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S0925-52140000163-0
potential to achieve different levels of heat toler- ance in ‘Kensington’ fruit using a range of condi-
tioning treatments and HWT. The optimum conditions for the development of fruit heat toler-
ance were also determined.
2. Materials and methods
2
.
1
. Plant material and common procedures Mango fruit Mangifera indica Linn. cv Kens-
ington were harvested and desapped in the field. Maturity was assessed in the field on a sample of
ten fruit that were similar in size and skin colour to those selected for the experiments using the
mango picking guide Holmes et al., 1990. The total solids TS levels of the fruit were deter-
mined in the laboratory according to AOAC methods AOAC, 1984. Upon arrival at the labo-
ratory, fruit were immediately transferred to 23°C for sorting and evaluation of initial skin colour.
Uniform unblemished fruit of size 380 – 440 g were selected for each treatment. All conditioning
treatments were carried out in a darkened cham- ber Jacobi et al., 1996. Fruit core temperature
was raised to the required conditioning tempera- ture during the first 2 h within the chamber and
subsequently maintained at this temperature for the duration. Immediately after conditioning, fruit
were transferred from the chamber directly to the bath for hot water treatment HWT. After HWT,
fruit were stored at 22°C together with untreated control fruit.
2
.
2
. Experiment
1:
optimum temperature for
8
h to generate heat tolerance
Green ‘Kensington’ mangoes were obtained from
a commercial
orchard near
Eumundi 26°28S, 152°58E around 0700 h on the 6th
February 1995 and transferred to the Brisbane laboratory within about 1h. Fruit were randomly
distributed to each treatment 14 fruittreatment. Treatments were: 1 untreated control fruit
were held continuously at 22°C; 2 conditioning for 8 h at 22°C followed immediately by a HWT,
where the fruit core temperature was raised to 47°C and held for 15 min using 48°C water, total
HWT time was 90 min; 3 conditioning for 8 h at 30°C followed immediately by HWT as described
above in 2, total HWT time was 85 min; 4 conditioning for 8 h at 38°C followed immediately
by HWT as described above in 2, total HWT time was 75 min; 5 conditioning for 8 h at 40°C
followed immediately by HWT as described above in 2, total HWT time was 65 min; and 6
conditioning for 8 h at 42°C followed immediately by HWT as described above in 2, total HWT
time was 60 min.
All evaluations were made 4 days after HWT, when the maximum differences between treat-
ments occurred. Fruit weight loss, skin colour objective and subjective, and the incidences and
severities of external and internal injuries were measured as described by Jacobi et al. 1996.
Fruit firmness was measured in Newtons N us- ing an Instron Universal Testing machine.
2
.
3
. Experiment
2:
increased heat tolerance deri6ed from conditioning treatments
Green ‘Kensington’ mangoes were obtained from an orchard near Kandanga 26° 23S, 152°
41E around 0600 h on the 7th February 1996 and transferred to the Brisbane laboratory within
3 h. Each treatment had ten fruit assigned to: 1 untreated control fruit were held continuously at
22°C; 2 conditioning for 8 h at 22°C followed immediately by a hot water treatment HWT
where the fruit core temperature was raised to 47°C and held for 15 min using 48°C water, total
HWT time was 110 min. This HWT time was then used as the standardised time for the remaining
treatments described below; 3 to 6 condition- ing for 8 h at 30, 38, 40 or 42°C followed immedi-
ately by HWT as described above in 2. The standardised HWT time was 110 min.
All evaluations were made as described for Experiment 1. Additionally, total soluble solids
TSS or brix and titratable acidity were measured on each fruit 4 days after treatment. TSS was
determined in the undiluted decanted juice from the macerated mesocarp of individual fruit using
an Abbe benchtop refractometer model 3T, Atago Co., Ltd., Itabashi-Ku, Tokyo, Japan cali-
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
