Postharvest Biology and Technology 20 2000 231 – 241
Peel tissue a-farnesene and conjugated trienol concentrations during storage of ‘White Angel’ × ‘Rome Beauty’ hybrid
apple selections susceptible and resistant to superficial scald
Bruce D. Whitaker
a,
, Jacqueline F. Nock
b
, Christopher B. Watkins
b
a
Horticultural Crops Quality Laboratory, Plant Sciences Institute, Agricultural Research Ser6ice, USDA, Building
002
,
10300
Baltimore A6enue, Belts6ille, MD
20705
-
2350
, USA
b
Department of Fruit and Vegetable Science, Cornell Uni6ersity, Ithaca, NY
14853
, USA Received 28 February 2000; accepted 20 June 2000
Abstract
In a 2-year study, fruit from eight red- and eight yellow-skinned ‘White Angel’ × ‘Rome Beauty’ hybrid selections were stored for 21 weeks at 0.5°C plus 1 week at 20°C and evaluated for the incidence and severity of superficial scald.
Five red-skinned R-03, R-20, R-22, R-48 and R-85 and three yellow-skinned Y-26, Y-55 and Y-65 selections were examined in both seasons. Peel-tissue samples taken at 0, 7, 14 and 21 weeks of storage were analyzed for
concentrations of a-farnesene and its conjugated trienol CTol oxidation products by HPLC with UV detection. Three red-fruited R-44, R-48 and R-85 and five yellow-fruited Y-38, Y-40, Y-55, Y-65 and Y-67 lines exhibited
scald symptoms. The remaining lines R-01, R-03, R-16, R-20, R-22, Y-07, Y-26 and Y-28 were free of scald. Overall, production of a-farnesene and accumulation of CTols were not closely correlated with scald susceptibility.
Data for the selections most prone to scald, Y-65, Y-40 and R-44, were consistent with the proposed role of
a -farnesene oxidation products in scald induction, but for Y-55 and R-48, which developed mild to moderate scald
and accumulated very little CTols, the data conflicted with the a-farnesene oxidation – scald induction hypothesis. Also, scald-resistant lines Y-07 and R-22 produced high levels of a-farnesene and reached CTol concentrations
comparable to those in several scald-susceptible lines. We conclude that if CTol do play a role in scald induction, there must be other mitigating factors of at least equal importance. Moreover, our findings support the proposal that
oxidation products of a-farnesene are not essential for scald development in fruit with severely compromised antioxidative defenses, but free radicals andor toxic volatiles generated by a-farnesene oxidation can exacerbate scald
symptoms. © 2000 Published by Elsevier Science B.V.
Keywords
:
Peel-tissue samples; a-Farnesene; Conjugated trienol www.elsevier.comlocatepostharvbio
1. Introduction
Superficial scald is a physiological disorder that arises in certain cultivars of apples and pears after
Corresponding author. Tel.: + 1-301-5046984; fax: + 1- 301-5045107.
E-mail address
:
whitakerbba.ars.usda.gov B.D.
Whitaker. 0925-521400 - see front matter © 2000 Published by Elsevier Science B.V.
PII: S 0 9 2 5 - 5 2 1 4 0 0 0 0 1 3 9 - 3
long-term cold storage Ingle and D’Souza, 1989. Largely on the basis of correlative data, the
sesquiterpene a-farnesene, and more directly its conjugated triene CT oxidation products, have
long been thought to play a central role in scald induction Huelin and Coggiola, 1968, 1970a; Anet
and Coggiola, 1974; Whitaker et al., 1998. How- ever, the biochemical mechanism of the disorder has
not been elucidated. Recent findings are consistent with the proposal that a volatile end-product of
a -farnesene oxidation, 6-methyl-5-hepten-2-one
MHO, causes the discoloration and death of hypodermal cells which lead to development of
scald symptoms Mir and Beaudry, 1999; Mir et al., 1999. Exogenous MHO induced scald-like brown-
ing in peel tissue from fruit of scald-susceptible apple cultivars Mir and Beaudry, 1999, and a
poststorage burst of MHO evolution was associated with intensification of scald symptoms in ‘Cortland’
apples Mir et al., 1999. Moreover, it was recently shown that the CTs which accumulate in the skin
and epicuticular wax of apple fruit during storage, mainly 7E,9E and 7E,9Z isomers of 2,6,10-
trimethydodeca-2,7,9,11-tetraen-6-ol
conjugated trienols in a ratio of 9:1 Rowan et al., 1995;
Whitaker et al., 1997, autoxidize at 20°C yielding MHO as a major product Whitaker and Saftner,
2000.
Regardless of the role of a-farnesene oxidation products, scald development very likely involves the
adverse effects of oxidative stress that occurs with prolonged storage at chilling temperatures Du and
Bramlage, 1995; Shewfelt and Purvis, 1995; Watkins et al., 1995; Rao et al., 1998. Huelin and
Coggiola 1970b and Anet 1972 first proposed that scald susceptibility or resistance in different
apple cultivars is, at least in part, determined by the efficiency of their natural antioxidant defenses.
Anet 1974 subsequently examined the levels of endogenous lipophilic antioxidants in the cuticle of
16 apple cultivars and found a correlation between scald resistance and the presence of antioxidant
levels sufficient to curtail a-farnesene oxidation during storage. Meir and Bramlage 1988 also
showed a negative correlation between scald suscep- tibility and high levels of unidentified lipophilic
antioxidants with an absorbance maximum at 200 nm in the cuticle of ‘Cortland’ apples. More
recent investigations have compared the accumula- tion of peroxides and lipid peroxidation products,
and the activities of enzymes that detoxify active oxygen species AOS, in peel tissue of scald-suscep-
tible and -resistant apple fruit stored at 0 – 1°C in air Du and Bramlage, 1994a, 1995; Rao et al., 1998.
Du and Bramlage 1994a, 1995, compared apple cultivars with wide variation in scald susceptibility
‘Cortland’, ‘Delicious’ and ‘Empire’ and found no marked changes in peroxidation or activities of
antioxidative defense enzymes related to scald de- velopment. In contrast, Rao et al. 1998 found a
close correlation between increasing levels of H
2
O
2
and lipid peroxidation products, declining perox- idase and catalase activities, and the occurrence and
severity of scald symptoms in fruit of susceptible and resistant ‘White Angel’בRome Beauty’ hybrid
selections grown at the same location under identi- cal conditions.
In their study of the ‘White Angel’בRome Beauty’ selections, Rao et al. 1998 assessed
changes in a-farnesene and CT levels spectrophoto- metrically using hexane- dip extracts of individual
fruit. Although a-farnesene and CT concentrations appeared somewhat higher in scald-susceptible than
in scald-resistant lines early in storage, a-farnesene synthesis and oxidation were not elevated in apples
that eventually developed scald symptoms. In addi- tion, Rupasinghe et al. 1998 determined that
a -farnesene synthase activity was about threefold
lower in scald-developing compared with scald-free ‘Delicious’ apple peel tissue. These findings chal-
lenge the hypothesis that oxidation of a-farnesene is directly linked with scald induction. Thus, the
present study was undertaken to rigorously examine
a -farnesene synthesis and oxidation in individual
red- and yellow-pigmented ‘White Angel’בRome Beauty’ selections during storage using HPLC – UV
analysis Whitaker et al., 1997, and to assess the relationship of a-farnesene metabolism to the inci-
dence and severity of scald after storage.
2. Materials and methods
