Produce Degradation Pathways and Prevention

Packaging and Produce Degradation 129

50% reduction in C 2 H 4 production was obtained at 1% O 2. This condition is attained
in ultra-low oxygen (ULO) storage of apples. Low oxygen partial pressure, also
generated in hypobaric storage, inhibits the activity of ACC oxidase [46] and, more
surprisingly, stimulates that of ACC synthase [47,48]. Hypoxia also reduces the
expression of genes involved in the maturation process and regulated by ethylene
[49]. Carbon dioxide, at an optimal concentration of 2%, sustains the in vivo activity
of ACC oxidase [50,51]. High CO 2 concentrations competitively inhibit ethylene’s
effects, preventing the autocatalytic induction of ACC synthase [52].

5.2.2.3 Effect of Other Gases

Some gases, including nitric oxide (NO) or nitrous oxide (N 2 O), were investigated
for reduction of ethylene production and expression.
Short exposure (2 to 24 h) to high NO^ concentration in anoxia can extend the
shelf life of climacteric and nonclimacteric plant tissues [53]. Nitric oxide, a natural
plant growth regulator, markedly delays senescence and maturation [54]. These
authors postulated a possible role of NO as a natural senescence-delaying plant
growth regulator agent regulating ethylene emission. Nitrous oxide at 80% with 20%
oxygen delayed maturation of tomatoes and avocados [55]. In both cases an inhibi-
tion of ethylene synthesis and action was noted, but the effects of N 2 O were not
reproducible.
Ethanol vapor also inhibits tomato maturation [56]. Ethanol reduces both eth-
ylene production and action [57]. This beneficial effect of ethanol vapor has not
been confirmed on numerous other fruits, including bananas, honeydew and canta-
loupe melons, peaches, pears, and plums [58]. These authors found that exposing
fruit to ethanol vapor resulted in either an accelerated or a reduced maturation rate.
Atmospheric relative humidity may also interfere with ethylene production and
maturation. Postharvest partial dehydration of avocados [59] and bananas [60] favors
ethylene production (for more information see Chapter 10).

FIGURE 5.8Ethylene production rate in broccoli as a function of atmosphere composition.
(From Zagory, D. and Kader, A.A., Food Technol., 42, 70, 1988. With permission.)

21

5

2

0

5

12

1

1.5

2

2.5

3

3.5

4

Ethylene production

(nmole/kg.h)

O^2 (%)

CO

2 (%)