Abstract
M.Sc.
Bananas are climacteric fruit which are characterised by a low rate of ethylene
production and respiration during the pre-climacteric phase, followed by a
sudden burst in ethylene production and respiration during ripening. Ethylene
is a gaseous plant hormone that accelerates the ripening of climacteric fruit.
In order to extend the shelf life of bananas the action or synthesis of ethylene
must be inhibited or delayed. Examples of such inhibitors are 1-
methylcyclopropene (1-MCP) an inhibitor of ethylene action, and
aminoethoxyvinylglycine (AVG), an inhibitor of ethylene synthesis. The
purpose of this research was to compare the effect of these two inhibitors on
ripening of bananas. 1-MCP acts by blocking the ethylene receptors
permanently. The results of this study indicated that 500 nL.L-1 1-MCP is
more effective in delaying ripening of banana than AVG, although AVG
delivered a better quality fruit in terms of colour. To be effective, bananas
must be pre-treated with 1-MCP before they exposed to ethylene. The results
also indicated that, the effectiveness 1-MCP to delay ripening decreases with
storage time. The results show that ethylene binding to its membrane bound
receptors is reversible if the exposure time to ethylene is less than 8 hours.
Exposure to ethylene for 8 hours or more results in irreversible binding.
However, binding only becomes permanent when exposure to ethylene
exceeds 16 hours. For this reason treatment with 1-MCP becomes ineffective
after exposure to ethylene for 24 hours due to the fact that ethylene has
bound irreversibly and permanently to its binding sites and cannot be
displaced by 1-MCP.