Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

460 POSTHARVEST BIOLOGY & TECHNOLOGY OF FRUITS, VEGETABLES, & FLOWERS
also showed the same results (Chanjirakul et al., 2007). This suggests that methyl jasmonate
treatment enhances antioxidant activity and free radical-scavenging capacity in fruits.
During inadequate antioxidant activity, free radicals cause membrane deterioration resulting
in CB in pears. Previous studies have reported the negative correlation between CB
and antioxidant metabolism. A reduction in antioxidant enzymes (SOD, POX, and CAT)
has been noticed in CB pears (Fu et al., 2007). 1-MCP treatment has shown higher CAT,
POX, and SOD activities in treated fruits compared to the control fruits during storage. Furthermore,
the incidence of CB in 1-MCP-treated fruits was 91% lower than in the control
fruits. During storage, 1-MCP-treated fruits exhibited a significant reduction in H 2 O 2 level,
which also indicates an increase in the free radical-scavenging capacity during the storage
(Larrigaudière et al., 2004). Therefore, 1-MCP enhances the activities of antioxidant enzymes
and reduces the occurrence of CB in pears. So, it eventually reduces the development
of physiological disorders during storage.
In apples, scald-susceptible fruits had higher H 2 O 2 concentration than scald-resistant
fruits during storage, and these lower H 2 O 2 concentrations were related to lower scald
development. In addition, higher activities of POX and CAT were also associated with
lower H 2 O 2 levels (Rao et al., 1998). Hence, antioxidants enhance the tolerance to environmental
stress. Lower contents of lipid-soluble antioxidants were noticed in scald-affected
apples during storage. In contrast, healthy fruits exhibited higher content of lipid-soluble
antioxidants. With 1-MCP treatment, the levels of lipid-soluble antioxidants, α-tocopherols,
and water-soluble antioxidants, ascorbic acid, phenols, and glutathione, were increased in
scald-affected apples. Moreover, 1-MCP treatment subsequently reduced the fruit scald
susceptibility during the storage (Shaham et al., 2003). Therefore, postharvest treatments
may reduce the storage stress in fruits and increase the levels of antioxidants that play an
important role in nutritional quality of the products.
21.6 Changes in sugars
Glucose, fructose, and sucrose are the main sugars in fruits. The right proportion of these
sugars attributes to the quality of the fruits. The sweetness of fructose is 1.8 times higher
than sucrose, whereas the sweetness of glucose is 3/5 of sucrose (Wang and Zheng, 2005).
The time of harvest significantly influences carbohydrate contents in fruits. The respiration
rate increases during postharvest storage at ambient temperature. An increase in respiration
enhances the consumption of sugars as substrates for several metabolic processes. The first
substrate used during respiration is sugar. A close relationship between respiration and sugar
levels was noticed in peaches during storage (Chen et al., 2006). There are several methods,
such as low temperature and CA storage and postharvest treatments, to delay postharvest
changes in the fruits and vegetables
21.6.1 Storage temperature and sugars
Low-temperature storage has been tried to maintain sugar levels in harvested fruits. Papaya
slices kept at 20 ◦ C had lower total soluble solids (TSSs) than slices kept at 5 or 10 ◦ C (Rivera-
Lòpez et al., 2005). Depletion of soluble solids at high temperature can be explained by a
high respiration rate. During storage of frozen papaya, an increase in glucose and fructose