Mango - Crop Post-Harvest: Science and Technology - page 112

proteins for the Aox and Ucp increased in a similar pattern
which suggested that their expression was not controlled in
a reciprocal manner but may be active simultaneously
(Considine et al . 2001).
During the maturation process, ethylene production
decreases and becomes undetectable for a short span of
time and then reappears upon ripening (Akamine & Goo
1973). Ethylene biosynthesis is an essential feature of
mango fruit ripening. The ethylene peak may precede,
coincide or lag behind the respiratory peak during mango
fruit ripening. According to Burg and Burg (1962), ethyl-
ene peak may precede or coincide with the respiratory
peak. While Biale and Young (1981) categorised mangoes
among the fruits in which ethylene rises after the respira-
tory peak. The temporal variation in the respiratory and
ethylene peaks is a very complex phenomenon and still
remains unfolded. Ethylene production is peaked at the
onset of climacteric phase of fruit ripening and the small
amount of ethylene present in the fruit at harvest is
sufficient to initiate ripening (Burg & Burg 1962; Mattoo
& Modi 1969). Ethylene is either directly or indirectly
involved in ripening associated changes. Post-harvest
handling conditions such as storage at chilling tempera-
tures impair the capacity of fruit to produce sufficient
ethylene to initiate normal ripening (Nair et al . 2004b).
The skin and pulp tissue of mango fruit also behave
differently with regard to ethylene production. The pulp
tissue is found to produce only about one eighth of the
ethylene and responded much less to exogenously applied
ACC than skin tissue in 'Keitt' mango during low
temperature storage (Lederman et al . 1997). The successful
manipulation of respiration and ethylene production rates
to delay ripening constitutes the hub of the post-harvest
management of mango fruit.

galactanases, arabinanases and pectin lyases (PL)
(Abu-Sarra & Abu-Goukh 1992; Ali et al . 1995; 2004;
Ashraf et al . 1981; Chaurasia et al . 2006; Mitcham &
McDonald 1992; Prasanna et al . 2003, 2005; Roe &
Bruemmer 1981). PG can exist in two forms either as exo-
PG or endo-PG. In mango, mainly exo-PG seems to act
and the activity of exo-PG increases as the fruit ripening
proceeds (Abu-Sarra & Abu-Goukh 1992; Ali et al . 2004;
Mitcham & McDonald 1992; Prasanna et al . 2003; Roe &
Bruemmer 1981). The differential rate of fruit softening in
mango is mainly due to the higher PG activity in the inner
mesocarp than the outer tissue (Mitcham & McDonald
1992). However, there are some contradictory reports
which suggested weak correlation between PG activity
and fruit softening (Abu-Sarra & Abu-Goukh 1992;
Lazan et al . 1986). Pectin esterases (PE) activity shows
either a declining or constant trend during ripening (Ali
et al . 2004; Ashraf et al . 1981; El-Zoghbi 1994; Prasanna
et al . 2003; Roe & Bruemmer 1981). Contrarily, an increase
in PE activity during ripening of African mango
'Irvingiagabonensis' has also been reported (Aina &
Oladunjoye 1993). The role of PE in softening of mango
fruit is still not well defined and understood. Despite high
pectin solubilization during softening of fruit, the changes
in the activities of PG and PE are not much higher in
mango unlike other fruits. Therefore, the implication of
other hydrolases in excessive softening cannot be ruled
out. Cellulases also show enhanced activities during
ripening (Abu-Sarra & Abu-Goukh 1992; El-Zoghbi 1994;
Lazan et al . 1986; Prasanna et al . 2003; Roe & Bruemmer
1981). The role of other hydrolases such as β-galactosidases,
galactanases, arabinanases (Ali et al . 2004; Lazan & Ali
1993; Prasanna et al . 2003, 2005) in mango fruit softening
has also been observed. The activity of β-galactosidase
increases seven fold during ripening of mango (Ali et al .
2004). Recently, the role of pectin lyase in ethylene-induced
softening in mango has also been established at the gene
level (Chaurasia et al . 2006). It is, therefore, the concerted
action of various hydrolases which bring about mass scale
changes in the content and properties of the cell wall com-
ponents. The fruit texture is an integral component of
quality and determines the consumer acceptance. For
extension of shelf life the post-harvest approaches should
be focused on maintaining the activities of these enzymes
at the lowest possible levels. The role of cell wall hydro-
lases in other growth and developmental processes cannot
be denied. It further requires a deeper understanding of the
sequence of events in the cell wall disassembly of mango
fruit so that some genetic engineering approaches can be
applied to have desirable genotypes.

Softening
Mango fruit undergoes extensive textural changes during
ripening. Fruit softening involves the degradation or modi-
fications of cell wall polymers by the synergistic action of
various cell wall hydrolases. Cell wall polymers such as
pectin, cellulose and hemicellulose undergo substantial
transformation and solubilization during ripening of fruit
which result in cell wall disintegration and cause softening
of fruit. There is a rapid increase in water soluble pectin
(WSP), chelator-soluble polyuronides, chelator soluble
carbohydrates and a decrease in total polyuronides in
mango during ripening (Ali et al . 2004; Chaurasia et al .
2006). The cell wall hydrolases implicated in pectin depo-
lymerization in mango are polygalacturonases (PG),
pectinesterases (PE), β-1,4-glucanases, β-galactosidases,