Postharvest Biology and Technology 18 2000 191 – 199
Hypobaric storage removes scald-related volatiles during the low temperature induction of 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 23 November 1999
Abstract
‘Law Rome’ and ‘Granny Smith’ apples were stored hypobarically in air at 5 kPa total pressure and also in air or controlled atmosphere CA at 1.5 or 3 O
2
with 0 or 3 CO
2
, for 8 months at 1°C. Fruit were placed under hypobaric storage immediately after harvest or after 0.5, 1, 2, 3, 4, 5 or 6 months storage in air at 1°C to determine
the effects of delaying imposition of hypobaric storage on ripening and scald development and on the production of a
-farnesene and its oxidation product 6-methyl-5-hepten-2-one MHO. If fruit were placed under hypobaric conditions within 1 month after harvest, scald did not develop. After a 3-month delay, scald development was similar
to that for fruit stored continuously in air. Both cvs. produced MHO which accumulated in their epicuticular wax when fruit were placed under hypobaric storage after a 1-month or more delay in air. MHO which had partitioned
in the epicuticular wax of fruit stored hypobarically after 2 or more months delay was released upon transfer of fruit to atmospheric pressure of 20°C; MHO accumulated andor was produced in direct proportion to the delay prior to
hypobaric storage. In another experiment with five apple cvs., the production rates of a-farnesene and MHO were low during hypobaric storage, but upon removal of fruit from storage after 7 months, the rates increased over a 7 day
period in air at 20°C and then sharply decreased afterward. After storage, a-farnesene and MHO production rates were similar and high for ‘Law Rome’, ‘Mutsu’, ‘Red Delicious’ and ‘Golden Delicious’ apples and were the lowest
for ‘Granny Smith’. Scald did not develop on any hypobarically stored fruit whereas it did on all cvs. except ‘Golden Delicious’ stored in air. It was proposed that hypobaric ventilation removes a scald-related volatile substance that
otherwise accumulates and partitions into the epicuticular wax of fruit stored in air at atmospheric pressure. © 2000 Elsevier Science B.V. All rights reserved.
Keywords
:
Apple; Superficial scald; Hypobaric storage; Volatiles; a-Farnesene; 6-Methyl-5-hepten-2-one; antioxidants; Chilling injury
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1. Introduction
Hypobaric storage is a system of storing com- modities while ventilating with air at less than
atmospheric pressure. The partial pressure of each component gas in air is reduced in direct propor-
Corresponding author. Tel.: + 1-517-3553286; 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 9 9 0 0 0 8 0 - 0
tion to the total pressure as a consequence of Dalton’s Law. Thus, at 10.1 kPa absolute total
pressure, the O
2
partial pressure is equivalent to 2.1 vv O
2
at atmospheric pressure, and the same is true for all other gases. The concept of
hypobaric storage of fruit was introduced by Burg and Burg 1966. Since then it has been
widely investigated Dilley, 1972, 1982; Spalding and Reeder, 1976a,b and reviewed Jamieson,
1980. Hypobaric storage extends the useful life of perishable commodities well beyond that
achievable by CA storage at the equivalent O
2
levels. Apples that are preclimacteric at harvest remain preclimacteric during hypobaric storage
at 10.1 kPa Dilley, 1972. Internal ethylene con- centration is decreased 10-fold which is well be-
low the level required to induce ripening. When this is coupled to a reduction in the rate at
which ethylene is produced at the reduced O
2
level equivalent to 2.1, an even further reduc- tion in ethylene concentration may exist within
the tissue. Moreover, the concentration of CO
2
produced in fruit metabolism is reduced, and one can assume that the concentration of metabolic
products such as ethanol, acetaldehyde and other compounds e.g. a-farnesene which have signifi-
cant vapor pressures at fruit storage tempertures would likewise be reduced under hypobaric ven-
tilation. a-Farnesene and its oxidation products have been implicated as factors in the superficial
scald disorder Anet, 1972; Song and Beaudry, 1996; Wang and Dilley, 1997; Mir et al., 1998;
Mir and Beaudry, 1999. Apple fruit do not de- velop scald when stored hypobarically Dilley,
1972, while fruit stored at the equivalent partial pressure of O
2
in CA storage can sometimes de- velop scald. The combined effects of lower pro-
duction rates of oxidatively produced metabolites at reduced O
2
levels and enhanced removal of substances with significant vapor pressures under
hypobaric storage conditions may at least par- tially explain prevention of scald. Hypobaric
storage thus offers an experimental system to elucidate the nature of these substances. It was
hypothesized that hypobaric storage controls scald by effectively decreasing the accumulation
of scald-related volatile compounds in fruit that may affect fruit metabolism such as ethylene,
a -farnesene and its oxidation product MHO. Hy-
pobaric storage was investigated to determine ef- fective treatment regimens and to gain insight
into the mechanism of scald control.
2. Materials and methods
