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ABSTRACT
In Italy, "Golden Delicious" apples are stored in
controlled atmosphere (CA) until May; but, CA apples suffer
from a lack of flavour at the end of storage. Improved fruit
quality and extended storage life can be achieved by storing
apples in ultra-low oxygen (ULO) atmosphere. The aim of this
work is to study the feasability of ULO storage for 'Golden
Delicious' apples, which is not a well-established technique
in Italy for this cultivar. Apples were harvested at the commercial
maturity in Val di Non Valley (600 m a.s.l.) and were stored
in 3500 q commercial storage rooms at 1°C (R.H. 97%) in
CA (1.5 % O2; 2.0 % CO2) and in ULO (0.9% O2; 1.2% CO2) for
seven months. At harvest and at the end of storage, apples
were analysed for flesh firmness, color (L*, a*, b*), titratable
acidity, soluble solids, sugars and organic acids by HPLC,
and ethylene and volatile composition (headspace cGC on intact
fruits) during ripening at 20°C. Quality parameters soon
after removal from CA and ULO storage rooms, defined ULO apples
as less ripe than CA fruits; total volatiles and volatile
compositions were similar for the two storage modes. With
the post-storage ripening, ULO stored apples produced more
total volatiles than CA; ULO atmosphere delayed maximum ethylene
and volatile productions, as well as the development of selected
volatiles. At tasting, ULO apples were firmer, more juicy
and sour and had a good distinct flavour. key words: Golden
Delicious apples, ULO, quality parameters, volatile composition.
INTRODUCTION
Controlled atmosphere (CA) storage is a well-established technique
used to extend the storage life of apples (Gorini, 1987).
Firmness, acidity, color and other quality parameters are
maintained in CA, whereas the ability of apples to produce
volatile compounds is suppressed during and after CA storage.
The aroma suppression depends on both the atmosphere composition
and the length of storage time (Yahia, 1994). Improved fruit
quality and extended storage life are achieved by lowering
the oxygen concentration to less than 1%, i.e. storing in
ultra-low oxygen (ULO) atmosphere (Brackmann et al., 1993).
The lower limit for oxygen, at which no accumulation of anaerobic
respiration products (acetaldehyde, ethanol, lactate) occurs,
.is connected to the cultivar, growing area conditions and
climate (Blanpied and Jozwiak, 1993; Meheriuk, 1993). In Italy
ULO storage is used to reduce physiological disorders in Red
Delicious and Granny Smith apples, but it is not widely used
for Golden Delicious apples (Eccher Zerbini et al., 1996;
Nardin, 1994). Therefore, the aim of this work is to study
the feasability of ULO storage for 'Golden Delicious' apples
in Italy, by evaluating physical and chemical characteristics
of stored fruits and ethylene and volatile composition during
ripening at ambient temperature.
MATERIALS AND METHODS
Apples (Malus domestica Borkh., cv 'Golden Delicious') from
11 year old trees, grafted on M9 rootstock were harvested
on 6th october 1994 at the commercial maturity in Val di Non
Valley (600 m a.s.l.) and stored in 3500 q commercial storage
rooms at 1°C (RH 97 %) in CA (1.5 % O2; 2.0 % CO2) and
in ULO (0.9 % O2; 1.2 % CO2) for seven months. The storage
conditions were obtained pulling down oxygen from 21% to 5%
over 8-10 hours. At harvest and at the end of storage, 30
apples were analysed for flesh firmness (11 mm plunger), color
(in reflectance with Minolta Chroma-Meter- CR-300, L*, a*,
b*), titratable acidity (TA) and soluble solids (SS). Then,
apples were pooled into six replications of five fruits and
each replication was analysed for sugar (sucrose, glucose,
fructose, sorbitol) and organic acid (malic, citric, succinic
and quinic acids) composition by HPLC on the aqueous extract
from the pulp (Forni et al., 1992; Vanoli et al., 1995). Other
3 replications of 8 fruits were put into glass flow-through
systems, and analysed for ethylene (Eccher Zerbini et al.,
1996) and volatile compounds during the ripening at 20°C
by dynamic headspace/capillary gas chromatography on intact
fruits (Rizzolo et al., 1992). At the end of the post-storage
ripening, fruits from each replication were analysed for flesh
firmness, TA, SS and, after being pooled into two groups of
4 fruits, for sugar and organic acid compositions. Data were
submitted to analysis of variance and the means compared by
Tukey test.
RESULTS
At harvest Quality parameters and organic acid and sugar compositions
of 'Golden Delicious' apples at harvest are shown in Tables
1 and 2, respectively. Ethylene and total volatile evolutions
during the fifteen-day postharvest ripening at 20°C (Figure
1) had a maximum between 11 and 13 days, reaching 53 mL L-1
kg-1 h-1 of ethylene and 41.5 mg kg-1 h-1 for total volatiles.
Maximum production of volatiles coincided with maximum production
of butyl acetate (20.73 mg kg-1 h-1), hexyl butanoate (0.31
mg kg-1 h-1), 2-methyl-propyl hexanoate (0.73 mg kg-1 h-1),
hexanol (0.35 mg kg-1 h-1), hexyl propanoate (0.50 mg kg-1
h-1), hexyl acetate (7.88 mg kg-1 h-1), butyl butanoate (1.05
mg kg-1 h-1), pentyl acetate (0.36 mg kg-1 h-1) and butanol
(2.88 mg kg-1 h-1).
After CA and ULO storage At the end of storage there were
differences between the fruit stored in the two atmospheres
(Table 3): ULO apples had higher L* value, were firmer and
contained lower quantities of succinc acid, citric acid, malic
acid, sorbitol, fructose and glucose.CA apples developed similar
amounts of total volatiles to ULO fruits (CA: 0.55 mg kg-1
h-1; ULO: 0.73 mg kg-1 h-1), having similar compositions,
with hexyl acetate and butyl acetate the main compounds.
With the post-storage ripening (Table 3), citric acid, malic
acid, quinic acid, fructose, glucose, sucrose, L*, a* and
b* increased, while TA and firmness decreased. Only for firmness
the interaction between storage atmosphere and days of post-storage
ripening was significative (F ratio = 5.066; P< 0.05 %).
After eleven days of post-storage ripening, ULO apples showed
a firmness not statistically different from that of CA apples
just removed from storage rooms; moreover, at the end of post-storage
ripening the firmness of the apples from the two storage modes
was not different. Just as at harvest, total volatile and
ethylene evolution coincided (Figure 2): ULO apples had maxima
productions of ethylene and volatiles at the end of post-storage
ripening, whereas CA apples after four days. With ripening,
ULO apples developed more total volatiles than CA fruits (CA:
3.77 mg kg-1 h-1; ULO: 6.61 mg kg-1 h-1). ULO storage delayed
the production of propyl acetate, propyl butanoate and butanol
during the post-storage ripening. At the end of post-storage
ripening (Table 4), ULO apples produced higher amounts of
hexyl butanoate, 2-methyl-propyl hexanoate and hexyl propanoate
than CA apples. A consumer test carried out after 7 days of
post-storage ripening , whose results are discussed by Mattè
(1997), defined ULO apples firmer, more juicy and sour and
with a good distinct flavour.
DISCUSSION
Storage atmosphere influenced quality characteristics, ethylene
evolution and volatile composition of 'Golden Delicious' stored
for seven months. Lowering O2 level from 1.5 % of CA storage
to 0.9 % of ULO storage, there was a delay in the maturation
process of apples; in fact after removal from storage rooms,
quality parameters defined ULO apples as less ripe than CA
fruits, according to Greene et al. (1993) and DeEll and Prange
(1993). Our work confirmed that CA storage suppresses volatile
production. During post-harvest ripening 'Golden Delicious'
apples produced 41 mg kg-1 h-1 of total volatiles compared
to 6 and 3 mg kg-1 h-1 for ULO and CA apples, respectively.
Moreover, the suppression of volatiles was particularly evident
for acetate esters, as found by Brackmann et al. (1993) and
Harb et al. (1994). The composition of storage atmosphere
had no effect on total volatile production and volatile compound
composition in apples just removed from storage rooms, but
it had a strong influence on post-storage ripening. With the
post-storage ripening, ULO atmosphere delayed maximum ethylene
and volatile compound production, as well as the development
of selected volatiles (propyl acetate, propyl butanoate and
butanol); however, at the end of post-storage ripening, ULO
apples developed more volatile substances than CA ones Our
results enphasize the feasability of ULO storage for 'Golden
Delicious' apples for the following reasons: higher firmness
and lower organic acid content at the end of storage, and
greater ability of producing volatiles with post-storage ripening.
(Paper presented at the International Conference on Controlled
Atmosphere Davis
- U.S.A. - 1997)
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