Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

184 POSTHARVEST BIOLOGY & TECHNOLOGY OF FRUITS, VEGETABLES, & FLOWERS
(Amanatidou et al., 2000), and strawberries (Wszelaki and Mitcham, 2000). Deng et al.
(2005) observed that decrease in firmness of grapes under different oxygen storage was
accompanied by a dramatic decrease in hemicellulose and moderate decrease in cellulose
and total pectins, which indicates that the softening in grapes is due to increased depolymerization
and degradation of cell wall polysaccharides. At higher oxygen storage, grapes
maintained firmness, which coincided with higher retention of cell wall polysaccharides.
The lower levels of water-soluble pectins in high-oxygen atmosphere were correlated with
delayed softening, and the activities of PG, PE, β-GAL increased to lower extent than air
storage, which indicates that higher oxygen might have inhibited relative enzyme activities,
reducing the degradation and depolymerization of pectin substances.
Cellulase activity in grapes increased slightly over time, and its activity was slightly
lower in high oxygen compare to air (Deng et al., 2005). In controlled atmosphere (CA)-
stored apples, ripening-related softening was inhibited after an initial loss of firmness.
However, softening resumed after transfer of apples to normal atmosphere storage at 8 ◦ C
(Ingham et al., 1998).
The retardation of carambola fruit softening by MAP and/or LT, which correlates closely
with delayed solubilization and depolymerization of the chelator-soluble polyuronides, may
partly be attributed to suppression of the increase in activity of the major wall hydrolases.
Suppression of the enzyme activities in fruit under MAP also appears to contribute to
increased tolerance of the carambolas to CI incidence (Ali et al., 2004).
Delayed (2 days at 20 ◦ C before storage) and controlled atmosphere (fruits stored at
10% CO 2 ,3%O 2 ) storage of nectarines fruits prevented wooliness during ripening of fruits
after 4- to 6-week storage at 0 ◦ C compared to fruits stored immediately in 0 ◦ C, 95% RH air
(Zhou et al., 2000). At the time of removal, the delayed stored fruits exhibited similar levels
of PG and PE transcripts but higher PG and lower PE activities compared to control fruits.
CA-repressed transcript levels of both PG and PE and activity of PG, but the PG activity
recovered during the 7-day ripening period. Whereas the endoglucanase activity declined
during ripening in all fruits, control fruits retained more activity than DS or CA fruits. On
the basis of these results, Zhou et al. (2000) have suggested that the ratio between PG/PE
at the time of removal of the delayed stored fruits or during ripening of CA stored fruits
plays a significant role in the development of fruit wooliness.
A hydrophobic coating formulated with maltodextrins, carboxymethylcellulose, propyleneglycol,
and a mixture of sorbitan esters was applied to preclimacteric “Manila” mangoes.
The fruit treated with the coating suffered less mesocarp softening along with concomitant
reductions of PG and cellulase (Cx) activities than did control fruit. After the initial storage
period, activity of PG increased steadily during further ripening of coated fruit (Diazsobac
et al., 1997).
Coating citrus with low-molecular-weight chitosan (LMWC, Mw = 15 kDa) improved
firmness and exhibited greater antifungal resistance than 2-(4-thiazolyl)benzimidazole
(TBZ), and its quality was maintained for longer (Chien et al., 2007).
8.12.6 Pathogen attack
In apple and tomato fruits, Penicillium expansum infection caused reduction in the molecular
mass of hemicelluloses, particularly in the xyloglucan. Xyloglucan endotransglucosylase/hydrolase
(XTH)-specific activity decreased drastically during the infection process