Agriculture Reference
In-Depth Information
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
L/L) (Hofman et al., 2001), however, because of its sensitive nature concen-
trations above 0.25
μ
L/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-
μ
-1,4-glucanase and polygalacturonase activities was as-
sociated with retention of firmness in avocado fruits. However, complete suppression of
polygalacturonase and inhibition of endo-
β
-galactosidase were ob-
served 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.
β
-1,4-glucanase and
β
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 concentration-
dependent 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 inhi-
bition 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 concentra-
tions 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
-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,
β
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