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Studies on Apple
MODELING RESPIRATION OF APPLE SLICES IN MODIFIED-ATMOSPHERE PACKAGES Modified-atmosphere packaging was used to provide
respiratory data for apple (Malus xdomestica Borkh.) slices at 0, 5, 10 and
15 °C. The maximum rate of O2 uptake increased with increasing temperature.
The lowest O2 partial pressure to which fruit could be exposed without
fermentation also increased with increasing temperature. A mathematical model of film
permeability data characterized the effect of fruit mass, film permeability to O2,
activation energy of O2 permeation, temperature, and the film type, area, and
thickness on O2 partial pressure for hermetically packaged apple slices. The
model identified a minimum (fruit mass x film thickness)/(film area) ratio for apple
slices, which would simplify package design calculations. Hexanal vapor inhibited hyphae growth of Penicillium
expansum and Botrytis cinerea on PDA media and on apple (Malus domestica
Bork.) slices. After 48 h exposure to 4.1 µmol·L-1 (100 ppm) hexanal, the
hyphae growth of both fungi was approximately 50% that of untreated controls. At a
concentration of 10.3 µmol·L-1 (250 ppm), neither fungi grew during the
treatment period, however, some growth of both fungi occurred 120 h after treatment. At
concentrations of hexanal vapor of 18.6 µmol·L-1 (450 ppm) or more, the
growth of both fungi ceased and the organisms were apparently killed, neither showing
regrowth when moved to air. When fungi were allowed to germinate and grow for 48 h in
hexanal-free air, a subsequent 48-h exposure to 10.3 µmol·L-1 hexanal slowed
colony growth relative to controls for several days and a 48-h exposure to 18.6 µmol·L-1
stopped growth completely. Concentrations of hexanal that inhibited fungal growth on PDA
also retarded decay lesion development on 'Golden Delicious' and on 'Jonagold' apple
slices. Hexanal was actively converted to aroma volatiles in 'Jonagold' and 'Golden
Delicious' apple slices, with hexanol and hexylacetate production strongly enhanced after
20-30 h treatment. A small amount of butylhexanoate and hexylhexanoate production was also
noted. Within 16 h after treatment, no hexanal could be detected emanating from treated
fruit. Since hexanal was metabolized to aroma-related volatiles by the fruit slices, the
possibility of hexanal being an essentially residue-less antifungal agent seems likely.
The possibility of developing a system for treating apple slices with hexanal in
modified-atmosphere packages was also examined. The permeability of LDPE film to hexanal
and hexylacetate was, respectively, approximately 500- and 1000-fold higher than LDPE
permeability to O2. The permeability of both compounds increased exponentially
with temperature, with hexanal permeability increased 6-fold while hexylacetate increased
only 2.5-fold between 0 and 30 EC. CHANGES IN CHLOROPHYLL FLUORESCENCE OF APPLE FRUIT DURING MATURATION, RIPENING AND SENESCENCE Trends in chlorophyll fluorescence for ‘Starking
Delicious’, ‘Golden Delicious’ and ‘Law Rome’ apple (Malus xdomestica
Borkh.) fruit was examined during the harvest season, during refrigerated-air (RA) storage
at 0 °C, following RA and controlled-atmosphere (CA) storage and during a post-storage
holding period at 22 °C. Fluorescence parameters of minimal fluorescence (Fo), maximal
fluorescence (Fm), and quantum yield (Fm-Fo)/Fm; otherwise denoted as (Fv/Fm) were
measured. During ‘Starking Delicious’ fruit maturation, Fv/Fm declined with
time, with the sharpest decline occurring 7 days after the ethylene climacteric. During RA
storage, all fluorescence parameters remained constant for approximately 2 weeks then
declined with time for ‘Starking Delicious’ fruit. After Fv/Fm had declined to
approximately 0.7, scald development was initiated. When "high quality" (CA) and
"low quality" (RA) ‘Law Rome’ fruit were combined, Fv/Fm was used to
re-segregate fruit from the two storage regimes. Re-segregation was achieved with 75%
accuracy using a threshold Fv/Fm value of 0.685, with only 5% RA-stored fruit incorrectly
identified as high quality. The Fv/Fm value was consistently higher for CA stored fruits
than for RA stored fruits. During a post-storage holding period, Fo, Fm and Fv/Fm were
found to correlate well with firmness for ‘Starking Delicious’, but not for
‘Golden Delicious’ fruit. Fo and Fm were linearly correlated with hue angle for
‘Golden Delicious’ fruit. The accuracy, speed of assessment and light-based
nature of fluorescence suggests that it may have some practical use as a criterion to
assist in sorting apple or other chlorophyll-containing fruit or vegetables on commercial
packinglines. CHLOROPHYLL FLUORESCENCE AND WHOLE FRUIT SENESCENCE IN GOLDEN DELICIOUS APPLE Chlorophyll fluorescence was used as a non-invasive probe
to study senescence in refrigerated air-stored apple fruit. 72% of variable fluorescence
was quenched when the fruit surface was excited by a continuous source of light. Most of
the quenching was photochemical. DCMU completely prevented the quenching of variable
fluorescence in the whole fruit and photosynthetic O2 evolution in the peel
discs. Under air storage conditions, all fluorescence parameters studied generally
declined over time; the rate of reduction was maximal from day 3 to 12. While the Chl
content ·g-1 FW had a decreasing trend similar to that of fluorescence, the
ratio of Chl a/b remained unchanged during the entire period of air storage.
The capacity of peel discs to generate O2, via photosynthesis, declined as the
fruit aged. The trend of the decline in O2 evolution was similar to the trend
for Chl degradation. In contrast, variable fluorescence quenching was found to be
independent of chloroplast photosynthetic activity in the later stages of fruit
senescence. A Mehler type O2 reaction is suggested to account for large amounts
of variable fluorescence quenching in apple fruit. Chlorophyll fluorescence appears to be
a promising tool for estimating whole fruit senescence. Randolph M. Beaudry |
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