Mango - Crop Post-Harvest: Science and Technology - page 127

the high temperatures necessary to kill all stages of the life
cycles of fruit fly species have been found to be injurious
to the fruit (Jacobi & Wong 1992). However, the HWT
technology is a more cost effective alternative to vapour
heat treatment which is presently in use in Australia. The
HWT also offers certain additional advantages, such as
ease- of-use less time consuming, reliable, and it gives fruit
surface sanitation to exclude plant debris and disease
control (Couey 1989, Jacobi et al . 2001b). Disinfestation
protocols approved for use in mango consist of immersing
fruit in hot water held at 43-46°C for 65-90 min depending
upon the fruit size and shape whereas temperatures above
46°C may cause excessive damage to fruit (Sharp 1986;
Sharp et al . 1988, 1989; Sharp & Spalding 1984). For
large-size mangoes weighing up to 900 g, HWT at 46.1°C
for 110 minutes provided Probit 9 level quarantine security
against Mexican fruit fly ( Anastrepha ludens Loew)
without adversely affecting fruit quality (Shellie & Mangan
2002). However, certain pests such as the stone weevil
Sternochetus mangiferae (Fabricius) were not killed by
hot-water immersion treatment at 48-52°C for up to 90 min
and 54-70°C for up to 5 min (Shukla & Tandon 1985).

(1997), there is differential response of mango fruit tissue
to VHT with inner mesocarp tissue affected more than the
outer tissue when the fruit were treated either at 46°C for
160, 220 or 280 min or at 50°C for 120, 180 or 240 min.
Colour development and softening were reduced more in
inner than in outer mesocarp tissue. Although VHT is an
established quarantine treatment for mangoes it needs fur-
ther modifications to reduce the heat damage with minimal
effects on the ripening process. The retardation of heat pro-
moted fruit ripening is a challenging area of research and
needs some basic investigations to elucidate the underlying
mechanisms.

Heat treatments and fruit physiology
Ethylene biosynthesis is reversibly inhibited by the heat
treatments in mangoes (Ketsa et al . 1999a; Mitcham &
McDonald 1997). The heat treatment of mangoes (cv. Nam
Dokmai) at 38°C for 3 days suppressed and delayed the
ethylene peak by 5 days compared to control during ripen-
ing at 25°C. There was a partial recovery of ACC synthase
activity during ripening while ACC oxidase recovered fully
following heat treatment. However, sufficient ethylene
synthesis was recorded to cause fruit ripening (Ketsa et al .
1999a). Respiratory metabolism is also strongly influenced
by heat treatments in mangoes. Mitcham and McDonald
(1993) observed 3.5- and fivefold increases in respiration
rates of mangoes during heat treatment at 46°C for 3 or 4 h
and 48°C for 5 h, respectively. However, respiration rates
fell below that of control fruit after a subsequent 4 or 6
days at 20°C. This transient increase in respiration during
and after heat treatment could be related to heat-induced
stress (Mitcham & McDonald 1993).

Vapour heat treatment (VHT)
Vapour heat treatment involves the use of heated air
saturated with water vapour to heat the fruit to a specified
temperature and hold that temperature for a specified
period to ensure that all target pests are destroyed (Jacobi
et al . 2001b). The temperature of mango fruit at or below
the dew point causes the condensation of air moisture on
the fruit surface and thus heat transfer takes place by
conduction. Vapour heat has proven to be a very effective
quarantine treatment in mango. It has been adopted on a
large scale in many countries like Australia, Japan,
Philippines, Thailand and the United States (Jacobi et al .
2001b). However, disinfestation protocol requirements
depend upon the cultivar and the importing country. Vapour
heat treatment of 'Kensington' mangoes to a core tempera-
ture of 47°C maintained for 15 min has been shown to
exceed the Probit 9 security level for a quarantine
disinfestation treatment against major species of fruit flies
in Australia (Heather et al . 1997). The 47°C schedule is the
requirement for Australian mangoes to enter Japan. Jacobi
and Giles (1997) treated 'Kensington' mangoes with
vapour heat at 47°C for 15 min or a HWT at 53°C for 5 min
prior to VHT combined with either storage at 10°C for 5
days followed by 22°C for 5 days or storage at 22°C for 10
days. The HW-VHT combination with continuous storage
at 22°C produced better quality fruit with better skin colour
and sensory ratings. According to Mitcham and McDonald

Heat treatments and fruit quality
The development of an effective quarantine treatment is a
very difficult task with dual goals of achieving insect
mortality without adversely affecting the fruit quality. The
heat tolerance in mango fruit is governed by several factors
such as cultivar, harvest maturity, fruit size, pre-harvest
factors, method of heat application and pre-heat treatment
conditioning, etc. (Jacobi et al . 2001b). However, heat
treatments are known to accelerate the fruit ripening pro-
cesses which leads to uniform and better skin colour devel-
opment and softening in mangoes (Esguerra & Lizada
1990; Jacobi & Wong 1992; McGuire 1991; Mitcham &
McDonald 1993; Pesis et al . 1997; Spalding et al . 1988).
There is always a potential risk of heat injury in mango
fruit when subjected to heat treatments. The symptoms of
heat injury included peel pitting, lenticel darkening, skin
scalding, uneven skin colour development, starch retention