Heat Treatment for Enhancing Postharvest Quality - Postharvest Biology and Technology of Fruits, Vegetables, and Flowers - page 250

Table 11.1 Physiological benefit of thermal treatments to prevent chilling injury in horticultural crops

Crop Phenomenon/appearance Regime Temperature/time

HAT a 38 ◦ C/4 days or 42 ◦ C/2 days Apple Scald

38 ◦ /3-10 h then 40 ◦ /30 min Avocado Skin browning HAT then HWT

38 ◦ /60 min Internal browning, pitting HWT

38 ◦ /24hor55 ◦ /5 min Cactus pear Rind pitting, brown staining HAT or HWT

34-36 ◦ /48-72 h Citrus Rind pitting HAT

50-54 ◦ /3 min; 53 ◦ /2-3 min HWT

59-62 ◦ /15-30 s HWB

38 ◦ /2 days; 54 ◦ /20 min Mango Pitting HAT

47 ◦ /90-120 min; Persimmon Gel formation HWT

50 ◦ /30-45 min; 52 ◦ /20-30 min HAT

40 ◦ /20 h Green pepper Pitting HAT

42 ◦ /30 min Cucumber Pitting HWT

38 ◦ /2-3 days Tomato Pitting HAT

48 ◦ /2 min; 42 ◦ /60 min HWT

42 ◦ /30 min Zucchini Pitting HWT

a

HAT, hot forced-air treatment; HWB, hot spray and brush treatment; HWT, hot water treatment.

injury in “Fortune” mandarins (Martinez-Tellez and Lafuente, 1997), and reduced decay as
well as chilling injury in lemons (Rodov et al., 1995).
Both hot water and hot air treatments control chilling injury on a number of fruits. Citrus
has already been mentioned earlier. However, avocados, mangos, and persimmons can also
benefit from either hot air or hot water. Chilling injury was prevented in avocados by short
hot air treatments at 38 ◦ C (up to 10 h), or by 30 min in hot water from 39 to 42 ◦ C (Nishijima
et al., 1995; Florissen et al., 1996; Hofman et al., 2002). Persimmons, under similar hot air
or hot water treatments as avocados, also had less chilling injury (Burmeister et al., 1997;
Lay-Yee et al., 1997; Woolf et al., 1997a, b). Persimmons are an interesting case in which
the chilling-injury symptoms include a change in fruit texture to mealiness or gel, which
is related to changes in the pectin polysaccharide component of the cell walls of the fruit.
Two enzymes of pectin, pectin esterase and polygalacturonase, when they work in concert,
metabolize pectin to smaller moieties and lead to fruit softening. When polygalacturonase
is inhibited, but pectin esterase is still active, pectin polysaccharides can swell into a gel-
like structure. The high-temperature treatment of persimmons prevents low-temperature
inactivation of polygalacturonase and prevents the deleterious fruit texture changes.
Superficial scald is a low-temperature physiological disorder of certain apple and pear
cultivars that develops during prolonged low-temperature storage. Typically, early-harvested
and less mature fruits are most susceptible, but scald may also develop on fully mature
fruit. The disorder appears as browning of the skin as a result of damage to the hypodermal
cells. Scald development results from production of -farnesene and its auto-oxidation to

conjugated trienols. Generally, correlations between conjugated triene concentration and
scald occurrence are strong, but those between

α

α -farnesene and scald are variable (Meir and

Bramlage, 1988). -Farnesene typically increases rapidly during storage and then declines,

while conjugated trienes continue to increase (Watkins et al., 1995).
Prestorage heat treatments have been found to be effective in controlling scald for the
first 4 months of regular air storage, and for much longer if the fruits are held in controlled
atmosphere storage (Lurie et al., 1990). Hot air treatment has been effective in controlling

α