Agriculture Reference
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2002; Saftner et al., 2003; Defilippi et al., 2004; Bai et al., 2005; Kondo et al., 2005).
During ripening, the aliphatic alcohols are used for the biosynthesis of esters, and this
process is inhibited by 1-MCP. Ester volatile biosynthesis is mediated by alcohol acyl CoA
transferase (AAT). The expression and activity of apple alcohol transferase gene (
MdAAT2
)
was inhibited in 1-MCP-treated apples during storage (Li et al., 2006). In response to 1-MCP
treatment, the rapidly ripening summer apple “Anna” showed less fruity, ripe, and overall
aromas which resembled that from a less ripe apple (Lurie et al., 2002). This was due to
an inhibition of volatile ester biosynthesis and maintenance of alcohol levels in the treated
fruit.
Improvement or preservation of nutritional quality is a key aspect of any postharvest
technology. There are conflicting reports on the effect of 1-MCP on apple antioxidants.
In Granny Smith (Shaham et al., 2003) and Golden Smoothee apples (Vilaplana et al.,
2006), total antioxidant activity and ascorbate levels were not affected by 1-MCP. 1-MCP-
treated apples were under lower oxidative stress, having lower levels of hydrogen peroxide
and peroxidative markers. In another study, the total oxyradical scavenging capacity of
both “Delicious” and “Empire” apples was higher in storage when treated with 1-MCP
(MacLean et al., 2003). MacLean et al. (2006) also found that the flavonoid content of
the apple fruit was slightly higher in 1-MCP-treated fruit, and the anthocyanin levels were
preserved during storage. However, chlorogenic acid, a major apple flavonoid, was 24%
lower in 1-MCP-treated apples. Shaham et al. (2003) found no difference in flavonoid levels
between control and 1-MCP-treated apples during storage.
Ethylene production by apple fruit occurs both on and off the tree when the ripening is
initiated. Therefore, the effectiveness of 1-MCP application is influenced by the maturity/
ripening stage at harvest and by the period the fruits are held in cold storage before treatment.
These two factors are interrelated, as more mature fruit at the time of harvest produce
autocatalytic ethylene sooner than earlier harvested less mature fruit. The effect of any
delays between harvest and application of 1-MCP is influenced by the cultivar as well as
the type and length of storage (Mir et al., 2001; Watkins and Nock, 2005). In a comparative
study of two apple cultivars “Orin” and “Fuji” that show differences in ethylene production,
ethylene was inhibited by 1-MCP in “Fuji” apples even when treatment was delayed for
a week after storage (Tatsuki et al., 2007). The expression levels of two ethylene receptor
genes,
MdERS1
and
MdERS2
, and the ACC-synthase gene
MdACS1
were also inhibited in
“Fuji” apples by 1-MCP, while ACC-oxidase
MdACO1
was inhibited slightly. However, in
a high ethylene-producing apple, “Orin,” the later the 1-MCP application after harvest, the
lesser was the suppression of ethylene production and the expression of these genes. In a
comparison of apple peel and pulp and the responses of the ethylene biosynthetic pathway
to 1-MCP, it was found that ACC synthase and ACC levels were decreased in both peel and
pulp (Vilaplana et al., 2007). ACC oxidase was also inhibited but not totally. However, high
levels of malonyl ACC were found in 1-MCP-treated tissue.
Controlled atmosphere storage can prolong the effect of 1-MCP on both physical and
sensory qualities of apple fruit (Rupasinghe et al., 2000; Watkins et al., 2000). However,
1-MCP treatment and short-term air storage may replace the requirement for CA storage,
especially for maintaining quality of summer apples (Pre-Aymard et al., 2003), and of those
cultivars that show enhanced deterioration after 2-3 months of storage (Watkins et al., 2000;
Dauny and Joyce, 2002; Bai et al., 2005). In addition, 1-MCP treatment can be effective in
many places where CA rooms are not available.
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