Abstract:
In the UK, consumers and retailers demand that there be a continuous
supply of
onions all
year round. To meet this demand, prehavest and postharvest methods are
used to
improve onion quality and storage life. Onions are currently cured at 28°C for
3-6 weeks to seal the neck of the bulbs
thereby reducing disease incidence and esh
moisture loss. Onions are then transferred to
long term storage in ambient conditions or
cold
storage with controlled atmosphere 'storage or continuous ethylene depending on
their intended
storage duration. This study aimed to review and improve current UK
curing and storage
practises by investigating the biochemical, physiological and
molecular effects these
postharvest regimes have on the esh and skins of onion bulbs.
Reducing curing temperatures from 28°C to 20°C was found to reduce the oxidation and
degradation of avonols and anthocyanins, respectively, resulting in paler brown skins
and more intense red skins.
Following curing, onions intended for long term storage
can be stored in continuous
ethylene. This said, both ethylene and the ethylene binding
inhibitor, l-methylcyclopropene (1-MCP), applied for just 24 h before or after curing
reduced orion
sprout growth for up to four months storage. However, onion sprout
suppression beyond four months cold storage would still require continuous ethylene
treatment. To elucidate the mechanisms
by which ethylene and l-MCP reduce sprout
growth, the rst onion microarray was developed. A cluster ofprobes were found to be
down
regulated in response to ethylene alone or in combination with 1-MCP. This,
along with biochemical and physiological results, suggested ethylene and 1-MCP may
both reduce
sprout growth via different mechanisms by binding different ethylene
receptors.
