Agriculture Reference
In-Depth Information
The rates of respiration, ripening and softening can be further slowed by
storage at low temperatures in controlled atmospheres. The gas composi-
tion in a regular atmosphere (RA) store is
%O
,
.
%CO
and about
% N. If the oxygen content is lowered to
% the respiration rate of apples
will decrease by
% and increasing the carbon dioxide concentration de-
creases the respiration rate of apples by
%. In practice, the O
and CO
concentrations in controlled atmosphere (CA) stores vary with cultivar, O
ranging from
.
%to
% and CO
from
.
%to
% (Hardenburg
et al.
,
). Prolonged exposure to very low oxygen concentrations may result in
anaerobic fermentation and production of alcohol. Excessive CO
concen-
trations cause internal injuries. The correct gas regime can, however, extend
the storage life of the fruit by
%, or even double it, compared with
RA cold storage. Further benefits can be obtained by rapid CA storage in
which optimum gas environments are obtained within
-
hours after sealing
the store, and by low oxygen storage with
%O
, which inhibits the de-
velopment of superficial scald, internal breakdown and fruit softening. The
retention of firmness in store of 'Golden Delicious' apples and some pears
is improved if they are exposed to
-
.
-
%CO
for
-
days before adjust-
ment to conventional CA conditions (Couey and Olsen,
; van der Merwe,
b). For some other apple cultivars this treatment is only effective if com-
bined with low-ethylene storage (Stow,
). High CO
concentrations (
-
%) can halve respiration rates (Fidler,
) and lower ethylene production
(Chavez-Franco and Kader,
), so their mode of action on firmness may be
complex.
In general early harvesting, well in advance of the respiration climacteric,
results in lower rates of respiration over the first few weeks of storage. Such
fruits are firmer and maintain this advantage during storage but may have
countervailing disadvantages in terms of size, colour, sweetness and aroma
production (Song and Bangerth,
). Picking date also has a marked effect
on physiological disorders and its optimization depends on a large number of
factors other than effects on respiration.
Respiration rates can be reduced by high fruit calcium content and by
control of ethylene production. These factors also have other major roles
regarding fruit quality.
Effects of ethylene
Ethylene has long been known to enhance fruit ripening and to increase the
activity of a number of enzymes associated with this (Abeles,
). It regu-
lates cellulase, chlorophyllase, invertase, laccase, malate dehydrogenase and
polygalacturonase. The rise of ethylene production that accompanies the cli-
macteric appears to be a key regulatory event in the development of most
