Oxygen and CO
2
contents were determined using an O
2
electrode Citicell CS type, City Technol- ogy Ltd., London, UK in series with a miniature
infra-red CO
2
transducer Analytical Develop- ment Company, Hoddesdon, UK with O
2
-free N
2
as carrier gas flow rate 580 mm
3
s
− 1
. Output signals were analysed using integrators Hewlett
Packard, model 3394A. Commercially prepared standards, BOC Special Gases, Wellington, NZ
were used for calibration of the gas analysers 2.05 kPa CO
2
, 5.1 kPa O
2
or 10.01 kPa CO
2
, 20.1 kPa O
2
, when held at one standard atmosphere total pressure.
2
.
4
. Data analysis For experiment 1, differences between samples
taken from flesh or cavity by direct removal and those from chambers held on to the fruit surface
with frames were analysed separately by time GLM procedure; SAS Institute, 1988. Values for
k
2
for the equilibration of both O
2
and CO
2
in chambers over wounded surface experiment 1
and intact cuticle experiment 2 were obtained by non-linear regression SAS Institute, 1988 of p
O
2
ch,t
and p
CO
2
ch,t
against time using Eq. 6. Before analy- sis, data at any given time were standardised by
dividing by the final values when equilibration was complete for these variables in chambers
over wounded surface, which were taken to repre- sent internal atmosphere composition. The same
general form of function as that in Eq. 6 was fitted to longer term data from experiment 2 to
characterise physiological drift in internal atmo- sphere estimates with time.
3. Results
3
.
1
. Experiment
1
Analysis of standardised data for equilibration of both O
2
and CO
2
in chambers adhered over wounded areas on the fruit surface revealed con-
sistent and rapid equilibration of both gases Fig. 1A and B, respectively. Values for k
2
, and corre- sponding estimates for surface permeance and t
0.99
were similar for O
2
and CO
2
. There was some indication of downward drift in CO
2
values with longer equilibration periods Fig. 1B.
Quasi-steady state levels of CO
2
in the cham- bers over wounded fruit surface underwent con-
tinuous decline from the time when the chambers were first equilibrated with the internal atmo-
sphere of the peppers Fig. 2B. On a gross scale, levels of O
2
in chambers were approximately con- stant throughout the experiment except for peri-
ods of a few hours following flushing chambers with nitrogen Fig. 2A, although the slight ap-
parent upward drift in O
2
values was consistent with the decline in CO
2
. Neither flesh nor cavity atmospheres were affected by wounding data not
Fig. 1. Changes with time in atmosphere composition within chambers adhered on the surface of pepper fruit at 20.4°C
following flushing with nitrogen at t = 0: A O
2
and B CO
2
contents for wounded surface experiment 1 and C O
2
and CO
2
contents for intact cuticle experiment 2. Values repre- sent averages of eight peppers. Data were standardised to
adjust for variation in internal atmosphere composition of individual fruit. Fitted lines were obtained by non-linear re-
gression using Eq. 6; parameter values are presented in Table 1.
Fig. 2. Long term changes with time after wounding t
aw
, h in partial pressures of A O
2
p
O
2
ch
, kPa, and B CO
2
p
CO
2
ch
, kPa in chambers adhered over wounded areas on the surface
of pepper fruit at 20.4°C. Chambers were flushed with N
2
at 16 and 64 h, denoted by arrows, and measurements made at 0,
0.5, 1, 4 and 12 h after flushing. Values represent averages of eight peppers; the line in B was obtained by fitting the
following function to data for times after flushing greater than 2 h: p
CO
2
ch
= 1.02 9 0.078 + 1.39 9 0.070 · 1 − t
aw
19.2 9 5.35 + t
aw
.
Samples of flesh atmosphere taken by direct removal consistently contained less O
2
and more CO
2
than samples similarly removed from the fruit cavity. Average values for cavity values mi-
nus flesh values were 1.1 9 0.12 kPa O
2
and −
0.68 9 0.044 kPa CO
2
S.E.M. had 46 degrees of freedom in both cases, with no effect of
wounding or time. For the final destructive sam- pling of fruit with surface chambers, flesh samples
had similar O
2
contents to those removed from chambers data not shown. In contrast, there was
a marked elevation of CO
2
level in direct removal samples relative to their chamber counterparts,
regardless of the level of CO
2
level in the fruit cavity, which ranged from 0.3 to 0.8 kPa. Average
Fig. 3. Changes with time in A O
2
and B CO
2
partial pressures in samples of cavity, flesh and chamber atmospheres
taken from in sweet pepper fruit at 20.4°C. Values represent averages for eight peppers. Chamber samples were taken re-
peatedly on the same fruit. Destructive, direct removal samples from flesh and cavity atmospheres were taken on a fresh batch
of fruit each time, combining data from fruit with and without surface wounding. Error bars are standard errors of means for
comparison of means obtained on a single occasion.
shown. The initial downward drift of CO
2
and upward drift of O
2
levels in flesh and cavity atmospheres with time, averaged over wounded
and control treatments, was similar to that in samples taken from chambers over wounded fruit
surface Fig. 3A and B. There were subsequently some apparently random deviations in the de-
structive samples from the consistent overall trends detected through analysis of chamber con-
tents. Differences between flesh and chamber con- tents became statistically significant for CO
2
after 76 h P B 0.01 on each occasion but were only
significant at one measuring time for O
2
tw = 88 h; P B 0.05.
Table 1 Values for the exponential decay constant from Eq. 6 k
2
, s
− 1
, fruit surface permeance to gases P
j
, pmol s
− 1
m
− 2
per Pa, calculated using Eq. 8 and 99 equilibration time t
0.99
, h; calculated using Eq. 7 for chambers adhered to pepper fruit surface at 20.4°C for both O
2
and CO
2
for experiments 1 and 2
a
O
2
Variable CO
2
S.E. Average
Average S.E.
Experiment
1
wounded 0.103×10
− 4
− 3.77×10
− 4
− 3.97×10
− 4
0.045×10
− 4
k
2
s
− 1
9001 P
j
pmol s
− 1
m
− 2
per Pa 234
8548 103
t
0.99
h 0.08
3.22 3.39
0.04 Experiment
2
intact k
2
s
− 1
0.358×10
− 6
− 4.23×10
− 6
− 43.6×10
− 6
3.55×10
− 6
1.95 237
P
j
pmol s
− 1
m
− 2
per Pa 19.3
23.0 24
29.3 302
2.14 t
0.99
h
a
Permeance values calculated for experiment 1 assume negligible contribution of intact cuticle to measured permeance.
elevation of CO
2
levels in flesh samples above those taken from the chambers was 0.51 9 0.051
kPa, whilst the elevation in CO
2
level in the flesh relative to samples from the fruit cavity was
0.77 9 0.057 kPa. Thus, overall difference between fruit cavity and chamber contents was slight but
statistically significant 0.26 9 0.091 kPa.
3
.
2
. Experiment
2
Rates of change of gas composition were much slower for chambers over intact cuticle than for
those over wounded surface in experiment 1 Fig. 1 and corresponding k
2
values were very much smaller Table 1. For O
2
, the absence of wound- ing decreased the magnitude of k
2
by 99 whilst that for CO
2
was reduced by 90. Val- ues for t
0.99
were correspondingly increased. Equi- libration of O
2
contents required about ten times as long as equilibration of CO
2
. Estimates of permeance to O
2
ranged between 16 and 36 pmol s
− 1
m
− 2
per Pa. Average permeance to O
2
was only 10 of that to CO
2
; similarly, the relation- ship between permeances to the two gases had a
slope of about 10 Fig. 4.
4. Discussion
