Agriculture Reference
In-Depth Information
where it is ripened and then distributed to consumers
(post-climacteric phase). The duration of the pre-climacteric
phase is the green-life of the fruit when it is firm and is
characterized by a low respiration rate and a green peel.
Ripening begins with autocatalytic ethylene (C
2
H
4
) produc-
tion and the climacteric rise in respiration. This phase is
noted for its high respiration rate and large changes in fruit
chemistry and physical attributes. The peel changes from
green to yellow, starch in the pulp changes to sugars and
flavour and aroma compounds are produced. The fruit sof-
tens and becomes ready to eat. The shelf life of the fruit is
best defined as the time between two different stages of
yellowing of the peel and is distinct from green-life. At the
end of shelf life the processes of senescence dominate and
the fruit becomes over-ripe. These definitions of green-life
and shelf life are not used consistently through the litera-
ture as some authors include green-life with shelf life.
'Green-life' and 'shelf life' are descriptive terms used
for convenience and do not have any underlying physiological
meaning. For marketing and transport, it is often desirable
to extend the green-life of the fruit and a considerable
amount of empirical research has been conducted to deter-
mine the factors that influence green-life. At the retail
level, it can be desirable to extend shelf life. Empirical
knowledge is gained by subjecting the fruit to various
treatments with the objective of changing the green-life,
shelf life or both. Empirically we know that the magnitude
of green-life is affected by the conditions under which the
fruit were grown, the maturity of the fruit (often expressed
as its age or size), the presence of exogenous ethylene,
temperature, light, mechanical damage and fungal infec-
tions. The ripening phase begins with the autocatalytic
production of ethylene. We don't yet know the precise
connections between the external factors listed above and
when ripening begins, except that exposure of the fruit to
C
2
H
4
will stimulate autocatalytic C
2
H
4
production and
initiate the ripening process. In commerce, this knowledge
is used to end green-life in preparation for ripening and
distribution to consumers. The external factors present
during fruit growth influence either the internal production
of C
2
H
4
in the pre-climacteric phase, the sensitivity of the
fruit to C
2
H
4
, or both.
Complementing this empirical approach there is a need
to know about the processes and mechanisms that influ-
ence the growth, development and ripening of the fruit at a
physiological level. Sound management practices used
after harvest depend on knowledge of how the fruit works.
Progress in research on the post-harvest aspects of
bananas and plantains has been regularly reviewed (Gore
1914; von Loesecke 1949; Palmer 1971; Simmonds 1959,
1966; Stover & Simmonds 1987; Hassan & Pantastico 1990;
Seymour 1993; John & Marchal 1995; Robinson 1996;
Turner 1997; Muirhead & Jones 2000). The reviews of
Palmer (1971), Seymour (1993) and John and Marchal
(1995) emphasise the biochemical aspects of ripening, while
those of Stover and Simmonds (1987) and Robinson (1996),
which are topic chapters, take an industry perspective.
Muirhead and Jones (2000) provide an excellent coverage
of post-harvest diseases.
Our purpose here is to draw attention to the unique
features of the banana fruit after harvest and discuss
progress in published research on post-harvest physiology
and management of bananas and plantains.
Manipulation of green-life
Green-life and fruit growth
The banana fruit increases in size as it grows and its green-
life decreases exponentially as it matures (Peacock &
Blake 1970; Turner & Rippon 1973; Srikul & Turner
1995). Indeed, green-life can be taken as a quantitative
measure of the immaturity of the fruit (Peacock & Blake
1970). In any given situation, the link between green-life
and growth is close, but there is sufficient separation to
cause problems in transport when some fruit ripen while
others remain green ('mixed ripe' or 'premature ripe'),
even though the fruit may be the same size or age. The
work of Turner and Rippon (1973) and Srikul and Turner
(1995) shows that management practices can change the
rate of growth independently of the rate at which green-life
changes during development. For example, increased N
supply and soil water deficit promote tendency to ripen
(i.e. reduce green-life), but N supply increases fruit growth
rate while soil water deficit reduces it. Experiments on the
effect of management practices on green-life usually only
measure the green-life of the fruit at the end of the experi-
ment and don't account separately for changes in fruit
growth and green-life. In these experiments the impact
of the treatment on the growth rate and green-life is
confounded (Ramsay
et al
. 1990). This may not be too
much of a problem, depending on one's objectives.
If the 'mixed ripe' problem is seasonal, harvesting fruit
that is less mature reduces the problem. In this case it
is necessary to sacrifice some yield, because the fruit is
thinner, but it ensures that fruit are more likely to reach the
market in a hard green condition.
Temperature
Low temperature during storage extends fruit green-life
(Blake & Peacock 1971) and is the main strategy used
commercially, although it is expensive. The temperature
