Mechanical Injury of Fresh Produce 93
Golden Delicious apple slices continued to respire intensely until at least day 4,
when there was a peak in CO 2.^122 Longitudinally cut green-tip bananas have higher
respiration rates during storage than those sliced into transverse or obtuse sections.^123
Maturity may also influence respiration rate of damaged plant tissues. Allong et
al.^124 reported that in mature-green Julie and Graham mangoes, respiration rates are
highest in cut fruit immediately after slicing, decrease significantly within the first
12 h of storage at both 5 and 10°C, and remain at levels above that of intact fruit
throughout the storage period. The effect of slicing on half-ripe and firm-ripe fruit
was an initial increase in respiration rate followed by a decline to levels equal to
that of intact fruit. 1-Aminocyclopropane-1-carboxylic acid (ACC) increases in cut
mangoes relative to the whole fruit.^125
Respiration rates of cut produce generally increase with an increase in storage
temperature and ripeness.61,117,126 The Q10 in several fresh-cut commodities stored
at 0 to 10°C are usually higher; only a few are lower than in the whole product.^115
The Q10 is greater in the 10 to 20°C temperature range for most cut fruits and
vegetables, apparently because of the rapid deterioration at these temperatures.
Respiration in mechanically damaged apricots varies depending on storage temper-
ature and fluctuations in temperature.^127 Forced-air cooling may be used to reduce
the respiration rate of mechanically damaged fruit. Damaged plums before precool-
ing showed a respiration rate double that of damaged fruit after precooling during
storage.^83 Respiration rates are reported to increase with storage time in fresh-cut
tomatoes^128 and melons.^129 Fresh-cut pears maintained respiration activity over a
period of 15 days at 3°C.^130 Reduction of storage temperature of damaged lettuce
from 37 to 10°C caused a decrease in respiration rate, but reducing the temperature
further to 4°C did not affect the respiration rate.^131 Lowering atmospheric oxygen
concentration reduced respiration rate. Storage in a low-oxygen atmosphere will
generally decrease respiration rate.125,126,132
The increase in respiration rate in freshly wounded plant tissue appears to be
accompanied by rapid cell expansion. Asparagus cells respond to wounding and to
the culture medium by rapid cell expansion on day 3 postisolation, which precedes
cell division by 24 h.^133 Cell expansion was accompanied by a large rise in respiration
rate and a massive increase in RNA synthesis through the generation of wound-
enriched mRNA populations.
4.8.2 ETHYLENE
Ethylene is synthesized naturally during plant development, fruit ripening, leaf
senescence, and responses to stress and pathogens. Synthesis is by reactions involv-
ing a cycle in which the amino acid methionine participates in the formation of
ACC, ACC synthase being a key enzyme in this pathway. Ethylene production is
stimulated when plant tissues are injured. Wounding increases activity of ACC
synthase and results in the accumulation of ACC that is subsequently oxidized to
ethylene. Wound ethylene is believed to be involved in the increased respiration of
tissues,^134 which differs among fruit products.^58
Ethylene exerts its action through^ a complex regulation of its own biosynthesis,
perception, and^ signal transduction135,136 that leads to dramatic changes in gene