Postharvest Biology and Technology 18 2000 201 – 213
Initial low oxygen stress controls superficial scald of apples
Zhenyong Wang, David R. Dilley
Department of Horticulture, Michigan State Uni6ersity, East Lansing, MI
48824
, USA Received 31 January 1999; accepted 13 December 1999
Abstract
The effectiveness of initial low oxygen stress ILOS to control apple scald without postharvest application of scald inhibitors and fungicides was investigated. Scald susceptible ‘Granny Smith’, ‘Law Rome’, ‘Red Delicious’ and not
susceptible ‘Idared’ fruits were harvested preclimacterically and treated at 1°C with 1 ILOS pretreatment or 2 no pretreatment as control. Fruit were then stored at 0.5 – 1°C in 3 O
2
with 0 CO
2
, 1.5 O
2
with 3 CO
2
, or 0.7 – 0.8 O
2
with 3 CO
2
in flow-through controlled atmosphere CA or in air. ILOS of 0.5 and 0.25 O
2
for 2 weeks resulted in excellent control of scald when fruits were subsequently held in CA 3 O
2
, 0 CO
2
. Initial treatment with 0.25 O
2
for 2 weeks, and when this treatment was supplemented with an additional 2 weeks of low O
2
stress after 2 months of storage, were more effective treatment regimens for scald control than all other treatments. ILOS followed by CA storage at 1.5 O
2
gave complete control of scald. A commercial test of initial low O
2
stress confirmed its efficacy for controlling scald in several cultivars of apples. The production of a-farnesene and its volatile
oxidation product 6-methyl-5-hepten-2-one MHO was inhibited by initial low O
2
stress treatments and 1.5 O
2
CA. The 0.25 O
2
initial stress treatment caused stronger inhibition of a-farnesene and MHO production than 0.5 O
2
initial stress treatment. The accumulation of MHO was related to scald development of apples. © 2000 Elsevier Science B.V. All rights reserved.
Keywords
:
Apple; Superficial scald; Initial low O
2
stress; Volatiles; a-Farnesene; 6-Methyl-5-hepten-2-one www.elsevier.comlocatepostharvbio
1. Introduction
Superficial scald of apples is a physiological disorder which, following long-term storage, has
the potential to destroy the market value and utility of millions of tons of fresh apples annually
Wang and Dilley, 1999. The disorder is pre- vented commercially by postharvest drench treat-
ment with diphenylamine DPA Smock, 1957. This drench treatment must include a fungicide to
prevent decay development. Numerous countries have banned the use of DPA or importation of
DPA-treated fruits, which mandates development of alternative methods to control scald.
It has been proposed that apple fruit may pos- sess at harvest or may acquire after harvest resis-
tance to scald Gallerani et al., 1990; Barden and Bramlage, 1994a,b. It is speculated that the skin
browning associated with the disorder results
Corresponding author. Tel.: + 1-517-3553286 or + 1-517- 3557483; fax: + 1-517-3530890.
E-mail addresses
:
wangzhe1pilot.msu.edu Z. Wang, dil- leypilot.msu.edu D.R. Dilley
0925-521400 - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 5 - 5 2 1 4 0 0 0 0 0 6 7 - 3
from autooxidative processes that disrupt cell membranes and are brought about by depletion
of endogenous antioxidants such as ascorbic acid or a-tocopherol during low temperature storage
Meir and Bramlage, 1988. Free-radicals such as hydroxyl OH, hydroperoxyl HO
2
and super- oxide O
2 −
can attack and destroy lipid and protein macro molecular structures essential for
cellular function Anet, 1969; Halliwell and Gut- teridge, 1989; Stadtman, 1993 and subsequently
lead to scald symptom development. Extensive investigations in Australia Anet and Coggiola,
1974 and references cited therein indicated that scald results from the autoxidation of a volatile
sesquiterpene hydrocarbon a-farnesene 2,6,10- trimethyl-2,6,9,11-dodecatetraene in the fruit skin
Meigh and Filmer, 1969. Based on in vitro studies, oxidation of a-farnesene was hypothe-
sized to yield conjugated triene hydroperoxide free-radicals which injure the hypodermal cells
and give rise to the symptoms of scald Anet, 1969, 1972. However, Rowan et al. 1995 found
that in vivo only trace amounts of these were detectable; the major oxidation products that ac-
cumulated in apple peel were two 2,7,8,11-tetraen- 6-ol conjugated trienol isomers.
Scald development in ‘Granny Smith’, a culti- var very susceptible to scald, was correlated to the
oxidation of a-farnesene to conjugated triene hy- droperoxides Huelin and Coggiola, 1970; Filmer
and Meigh, 1971. Song and Beaudry 1996 found that 6-methyl-5-hepten-2-one MHO, a
volatile product of a-farnesene oxidation, caused a scald-like disorder when applied to peel tissue of
susceptible apple fruit. Scald can be induced by the conjugated triene CT products of a-far-
nesene oxidation, and the concentration and time of appearance of these products is related to the
severity of the disorder Anet, 1972. The scald inhibitor chemicals DPA and ethoxyquin are ef-
fective inhibitors of lipid peroxidation, and ethanol vapor which controls scald Scott et al.,
1995a; Wang and Dilley, 1996, 1997; Wang et al., 1997; Ghahramani and Scott, 1998a is a free-rad-
ical scavenger Halliwell and Gutteridge, 1989. Little et al. 1982 reported that scald of ‘Granny
Smith’ apples was largely controlled by an initial low O
2
stress followed by CA storage. Low O
2
could exert its action partly by increasing endoge- nous ethanol production Wang et al., 1997;
Ghahramani and Scott, 1998b. We have tested the concept that initial low O
2
stress prior to CA storage controls scald by inducing production of
ethanol and inhibiting a-farnesene synthesis and its oxidation to yield MHO. Initial low O
2
stress treatments were investigated to determine effec-
tive treatment regimens and to gain insight into the mechanism of scald control.
2. Materials and methods
