has been reinvestigated in recent years. Wiping ‘‘Granny Smith’ apples with commercial plant oils
canola, caster, palm, peanut, or sunflower re- duced scald after 4 months of cold storage Scott
et al., 1995. Wheat germ oil also reduced scald of ‘Delicious’ and ‘Granny Smith’ apples and ‘d’An-
jou’ pears in regular storage Curry, 2000. None of the treatments controlled scald to a satisfactory
level over an extended time, however.
Emulsions of various edible plant oils reduced scald in ‘Delicious’ apples, but were not as effective
as 2000 mg l
− 1
DPA Ju et al., 2000. On the other hand, when the plant oils were stripped of a-toco-
pherol B 5 mg kg
− 1
, emulsion treatments were as effective in controlling scald as commercial levels
of DPA Ju et al., 2000. Thus, the effectiveness of edible plant oil emulsions was reduced by the
natural titer of 500 – 800 mg kg
− 1
a -tocopherol. It
is not known whether stripped plant oils may also be effective in controlling scald in other cultivars
or species. a
-Farnesene is closely associated with scald de- velopment in apples and pears Ingle and D’Souza,
1989; Chen et al., 1990b; Whitaker et al., 1997 and its biosynthesis appears to be regulated to some
degree by ethylene Watkins et al., 1993; Ju and Bramlage, 2000; Ju and Curry, 2000b. In previous
studies, oil-treated fruit were greener than control fruit when held at 20°C for 30 days Ju and Curry,
2000a or after 6 months at 0°C Ju et al., 2000, suggesting oil may delay ethylene-mediated fruit
ripening or senescence. Direct effects of oil treat- ments on ethylene and a-farnesene production, and
on fruit ripening or senescence have not been studied. Thus, the objective of this study was to
investigate the effects of stripped corn oil emulsions on ethylene biosynthesis, fruit ripening and senes-
cence, a-farnesene production and scald develop- ment, as well as on development of other storage
related physiological and pathological disorders in ‘Granny Smith’ apples and ‘d’Anjou’ pears.
2. Materials and methods
2
.
1
. Plant materials ‘d’Anjou’ pears Pyrus communis L. and
‘Granny Smith’ apples Malus x domestica Borkh were harvested from a commercial orchard near
Wenatchee, WA on 8 September and 6 October, 1998, respectively. Emulsions containing 60
stripped corn oil a-tocopherol reduced to B 5 mg l
− 1
, Aldrich, Milwaukee, WI were made by mixing six parts corn oil, one part Tween 60, and three
parts hot water 90°C with continuous stirring Ju et al., 2000. After cooling, the emulsion was diluted
to the selected concentration and used for fruit treatment. At harvest, ten fruit from each of three
replications were used for quality evaluation, and ethylene and a-farnesene measurement. Treatments
included dipping fruit in 2.5, 5 and 10 oil emul- sion or 2000 mg l
− 1
DPA solution. Because dipping fruit in water may increase fruit decay, untreated
fruit rather than fruit dipped in water were used as controls. Within 24 h of harvest, 240 fruit per
replication were dipped in solution for 3 min, allowed to air dry, placed in cardboard boxes, and
stored at 0°C for up to 8 months.
Internal ethylene was measured every month for 6 months immediately after cold storage without
warming. Ethylene and a-farnesene production in both peel and cortex tissue of apples and pears were
measured every month for 6 months immediately after cold storage plus 4 h at 20°C. Superficial scald
was evaluated after 6 and 8 months storage at 0°C both immediately after removal and after 7 days at
20°C. Senescent scald, coreflush, fruit firmness, skin color, soluble solids content SSC, and titrat-
able acidity TA were measured after 7 days at 20°C, following 6 or 8 months of cold storage.
2
.
2
. a-Farnesene and ethylene measurement a
-Farnesene in apple was measured using whole fruit by GS-MS with a solid-phase-micro-extrac-
tion SPME method Ju and Curry, 2000a. Twelve fruit from each of three replications were
taken from cold storage, warmed to 20°C for 4 h, and placed in a 4-l glass jar at 20°C. The jar was
connected to a flow-through system with a flow rate of 50 ml min
− 1
. After 2 h equilibration, a 100 mm polydimethylsiloxane probe Supelco, PA was in-
troduced into each jar and allowed to adsorb volatiles for 10 min. The probe was immediately
inserted into the injection port of a gas chro- matograph HP 5890, Hewlett Packard, CA.
Adsorbed volatiles were allowed to desorb for 3 min in the injector with a constant temperature of
250°C. Oven temperature was kept at 35°C for 6 min and increased to 250°C at a rate of 40°C per
min and then held for 2 min. Measurement of
a -farnesene is presented as units per kilogram fresh
weight per hour. One unit was defined as 1000 in abundance.
Internal ethylene in apple was measured by first taking a 0.5 ml air sample from the core area of ten
individual fruit in each replication followed by gas chromatography GC. A glass column 610 mm ×
3.2 mm i.d packed with Porapak Q 90 – 100 mesh was used. Oven, injector, and FID temperatures
were 50, 50 and 200°C, respectively. Gas flows for N
2
carrier, H
2
and air were 30, 30 and 300 ml min
− 1
, respectively. Tissue discs were used to measure ethylene and
a -farnesene production in apples and pears. Cylin-
drical tissue plugs were removed from fruit using a no. 9 brass cork borer 1.2 cm diameter and
divided into peel 3 mm thick, including epider- mis, hypodermis, and several layers of cortical cells
and inner 3 mm thick, mid-section of the flesh cortical discs. Each treatment included three repli-
cations and each replication contained twenty tis- sue discs. Discs were first washed with 1 wv
ascorbic acid solution and then put into a 20-ml test tube. After sealing the test tube with a rubber
septum, 2 ml of air was removed from the test tube to facilitate a-farnesene diffusion from the tissue.
A 100 mm polydimethylsiloxane PDMS probe was introduced into the test tube and allowed to adsorb
volatiles for 20 min. a-Farnesene was measured as described and presented as units per gram fresh
weight per min. One unit was defined as 1000 in abundance. Ethylene production rate was mea-
sured using GC by taking a 0.5-ml air sample from the test tube immediately following a-farnesene
measurement.
2
.
3
. Scald and coreflush e6aluation Scald was recorded as percent incidence using the
scale: 1 = 1 – 10, 2 = 11 – 33, 3 = 34 – 66, and 4 = 67 – 100 of the surface area affected. Scald
intensity was calculated as the mean incidence of the affected fruit.
Senescent scald in ‘Granny Smith’ was defined as a light brownish color that developed on the fruit
epidermis without the presence of irregular black- ening typical of superficial scald. Percent incidence
and intensity were recorded using the same scale and method as described above.
Core flush a pinkish brown color in the core area and flesh was assessed in fruit cut into four equal
parts longitudinally and presented as percent inci- dence.
2
.
4
. Fruit color, firmness, soluble solids content, and titritable acidity measurement
Fruit color, firmness, SSC and TA were quantified both at harvest and after cold storage
plus 7 days at 20°C using three replications of ten fruit. Fruit color was measured by the ‘L, a, b’
system using a chroma meter DP-301, Minolta, Osaka, Japan from which the CIELAB values a
and b presented as chroma, hue angle and ab ratio McGuire, 1992. Firmness was measured
with an electronic pressure tester EPT-1, Lake City Tech. Products Inc., Kelowna B.C., Canada
equipped with an 11-mm tip for apple and 8-mm tip for pear. Readings were made on two pared
sides of each fruit. SSC was assessed with a digital refractometer PR-1, Atago Co. Ltd., Japan on a
combined sample of juice extracted from ten fruits in each replicate. TA was measured by titrating 5
ml of juice extracted from 10 fruit in each replicate using a Standard pH Meter PHM 82, Radiometer
American, Cleveland, OH in conjunction with a Titrator TTT 80, Radiometer American, Cleve-
land, OH and expressed as percent malic acid equivalents.
2
.
5
. Post-storage ethylene treatment on
10
oil-treated fruit After 8 months storage at 0°C, 10 oil-treated
‘Granny Smith’ and ‘d’Anjou’ fruit that did not develop scald were placed in a 12-l plastic chamber
with constant air containing 0 or 12.5 mmol ethylene with a flowrate of 6 l h
− 1
. Fruit color,
firmness, SSC, TA, scald, coreflush, internal eth- ylene and ethylene production rate in fruit peel,
were measured or evaluated after 7 days at 20°C.
2
.
6
. Statistics Data were subjected to ANOVA and regres-
sion analysis using SAS Statistical Software SAS Institute, Cary, NC. Means were sepa-
rated using Tukey’s Studentized Range Test.
3. Results
