Heat Treatment for Enhancing Postharvest Quality - Postharvest Biology and Technology of Fruits, Vegetables, and Flowers - page 248

Chilling injury symptoms
Heated fruit
Fig. 11.2 Chilling injury symptoms in control fruit after storage at 2 ◦ C and normal ripening in fruit held at 38 ◦ C
before 2 ◦ C storage.
et al., 1997). Therefore, the inhibition of ripening may also be a consequence of a general
inhibition of gene expression at heat stress inducing temperature.
11.3 Effects on senescence
Broccoli senesces vary rapidly and the florets turn yellow after harvest as a result of chloro-
phyll degradation. Yellowing is one of the most important factors in quality degradation in
this and many other green vegetables. Reproductive structures within the florets produce
high amounts of ethylene, which play a role in broccoli senescence (Tian et al., 1994).
High-temperature treatment with 45 ◦ C hot water for 10 min (Tian et al., 1996, 1997), 45 ◦ C
for 14 min (Kazami et al., 1991a, b), 50 ◦ C for 2 min (Forney, 1995), or 50 ◦ C hot air for 2 h
(Terai et al., 1999) delayed yellowing of harvested broccoli florets and reduced the rate
of ethylene production. The different times and temperatures that were successful in this
crop may be due to the fact that each study used different broccoli cultivars. The hot water
treatments also slowed the loss of soluble proteins and ascorbic acid (Kazami et al., 1991b;
Tian et al., 1997). The enzymes that promote chlorophyll degradation, chlorophyllase and
peroxidase, were inhibited in the hot air-treated broccoli, while they increased in nonheated
florets during storage (Funamoto et al., 2002, 2003) (Fig. 11.3).
In a similar manner, hot moist air at 40 or 45 ◦ C from 30 to 60 min reduced the senescence
of harvested kale and collard leaves (Wang, 1998). Yellowing of the leaves was delayed,
losses of sugars and organic acid were slower, and turgidity was maintained during storage