Agriculture Reference
In-Depth Information
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
Method a
Temperature ( C)
Fruit
Time
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Lurie (unpublished).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 han-
dling 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
50
49
48
47
46
45
44
43
42
41
40
Surface-HAT
Below surface-HAT
Surface-VH
Below surface-VH
Surface-HW
Below surface-HW
0
50
100
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).
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