Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

254 POSTHARVEST BIOLOGY & TECHNOLOGY OF FRUITS, VEGETABLES, & FLOWERS
Table 11.2 Response of fruits to various exposure times and temperatures with respect to phytotoxic effects
and aspects of ripening such as softening, skin color changes, sugar, and acidity
Phytotoxic
Fruit Method a Time Temperature ( ◦ C) symptoms Softening Color
Apples HA 96 h 38 N Firmer Increased
HA 96 h 43 Y Firmer Increased
Oroblanco citrus HA 4 h 46 N Softer Increased
HA 4 h 47 Y Softer Increased
Mango VH 15 min 46 N No effect No effect
VH 30 min 46 N Softer Increased
VH 30 min 47 Y Softer Increased
Lurie (unpublished).
a HA, hot air; VH, vapor heat.
(Ortega-Zaleta and Yahia, 2000). This is true of other fruits as well (Table 11.2). Hot water
treatments can also result in damage to the epidermis of the commodity. Red ginger flowers
heated in water at 49 ◦ C for 12–15 min had some damage to the inner bracts that resulted in
necrotic tissue (Hara et al., 1996). The authors also found that hot water treatment caused an
intensification of mechanical injury in flowers, emphasizing the importance of careful handling
of materials destined for heat treatment. Surface browning of peaches exposed to hot
water treatments increased with both time (1.5–5 min) and temperature (50–55 ◦ C) (Phillips
and Austin, 1982). Fruit differed in susceptibility because of seasonal and maturity effects.
Many researchers have shown that heating in moist forced air was less damaging to
the fruit than heating in hot water or vapor-heated air. Shellie and Mangan (2000) closely
monitored fruit surface temperatures during heating with hot water, moist forced air, and
water vapor-saturated air (vapor forced air) (Fig. 11.7). The temperature of the fruit surface
varied according to the heating medium used. Fruit surface temperature was coolest when
heated with moist forced air and reached only 81% of the temperature of the heating medium
after 5 min of exposure. The surface of the fruit heated with vapor-saturated air or hot water
reached 96% of the temperature of the heating medium within 5 min. During heating with
vapor-saturated air, the surface temperature of the fruit exceeded the air temperature after
about 20 min of heating and remained 1 ◦ C higher, while the surface temperature of fruit
Temperature (C)
50
49
48
47
46
45
44
43
42
41
40
0
50 100
Surface-HAT
Below surface-HAT
Surface-VH
Below surface-VH
Surface-HW
Below surface-HW
Time (min)
Fig. 11.7 Rate of heating of fruit at surface of 2 mm below the surface when heated in 48 ◦ C moist, forced-air
treatment (HAT), vapor-saturated, forced air (VH), or hot water (HW).