Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

ENHANCING POSTHARVEST SHELF LIFE AND QUALITY 145
7.3.2 Avocado
Unlike apples, avocados do not ripen on the tree, and the fruits begin the ripening process
after they are harvested. Avocados respond to 1-MCP in a concentration and time-dependent
manner (Feng et al., 2000; Jeong et al., 2002). An earlier study used excessive levels of
1-MCP (25 μL/L) (Hofman et al., 2001), however, because of its sensitive nature concentrations
above 0.25 μL/L inhibits ripening (Jeong et al., 2003; Adkins et al., 2005; Woolf
et al., 2005). The inhibition of ripening is associated with a delay as well as a decrease in
ethylene production and the respiratory climacteric (Feng et al., 2000, 2004; Jeong et al.,
2002, 2003; Hershkovitz et al., 2005). The treated fruits show increased firmness, delayed
softening, and change in skin color. 1-MCP also reduces the weight loss during storage
(Jeong et al., 2003).
The activities of enzymes involved in cell wall disassembly have also been evaluated
after subjecting avocado fruits to 1-MCP treatment (Feng et al., 2000; Jeong and Huber,
2005). Inhibition of both endo-β-1,4-glucanase and polygalacturonase activities was associated
with retention of firmness in avocado fruits. However, complete suppression of
polygalacturonase and inhibition of endo-β-1,4-glucanase and β-galactosidase were observed
in the later study (Jeong and Huber, 2005). However, even in the absence of any
measurable activity of polygalacturonase, 1-MCP-treated fruits lost nearly 80% of their
initial firmness after 24 days of storage at 20 ◦ C.
In the case of avocados, it is important that the 1-MCP treatment procedure does not
delay the ripening procedure excessively. A long delay in ripening is also associated with
an increase in fruit decay (Adkins et al., 2005; Wang et al., 2006). However, 1-MCP reduces
ethylene-induced storage disorders in storage (Pesis et al., 2002; Woolf et al., 2005), making
this an alternative approach for disease control.
7.3.3 Banana
Bananas are harvested at a mature green stage of maturity and ripened by the application
of ethylene. 1-MCP treatment of the fruits delayed ripening in a time- and concentrationdependent
manner (Jiang et al., 1999b; Harris et al., 2000; Bagnato et al., 2003). The
inhibition by 1-MCP was also dependent on the maturation stage. The ripening of immature
bananas is inhibited to a lesser extent than that of mature fruits by 1-MCP (Harris et al.,
2000). As well, once ripening is initiated by propylene treatment of mature green bananas,
1-MCP treatment does not inhibit the ripening processes effectively (Golding et al., 1998).
As in other fruits, a decrease in ethylene production and respiration rates and an inhibition
of softening were evident in bananas exposed to 1-MCP (Golding et al., 1998; Jiang
et al., 1999a, b; Macnish et al., 2000; Pathak et al., 2003; Pelayo et al., 2003; Lohani et al.,
2004). A lower level of soluble solids was detected in a study (Nascimento et al., 2006). As
in apples (Lurie et al., 2002), total volatile production was decreased and ester concentrations
were lower, while those of alcohols were higher in treated fruit (Golding et al., 1998).
A number of ripening-related genes were upregulated by ethylene treatment in banana, and
this increase was prevented by 1-MCP (Gupta et al., 2006). Two genes for enzymes induced
by ethylene are a fruit-specific expansin, MaExp1, and one for β-amylase. These enzymes
degrade starch into sugars, and both were inhibited by 1-MCP treatment (Trivedi and Nath,
2004; Nascimento et al., 2006). An ethylene-responsive, ripening-related expansin gene,