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PROJECT No.: ARS 532 Terminating Report

TITLE: Postharvest Treatments Which Reduce Scald

YEAR INITIATED: 1994-1995 CURRENT YEAR: 1999-2000

TERMINATING YEAR: 1999-2000

PERSONNEL: Eric A. Curry, Plant Physiologist

USDA, ARS, PWA, Wenatchee, WA

JUSTIFICATION:

Superficial storage scald is a disorder that develops on the apple fruit surface after

several months in cold storage. It occurs on the main apple cultivars grown in the

northwest and may be a major source of postharvest loss if not controlled. The

postharvest antioxidant chemical diphenylamine (DPA) has been an effective

inhibitor of the disorder on ‘Delicious’ and ‘Granny Smith’ apples. Over the course

of this project we have looked at a number of alternatives to DPA as well as

combinations of alternatives to reduce the amount of DPA needed to control

scald. These alternatives have included heated water, controlled atmosphere, and

addition of calcium, squalene, and various other experimental or purported scald

reduction agents. This report summarizes many of the experiments conducted

over the course of the project as well as specific experiments conducted this past

year.

OBJECTIVE:

The objectives of this project were to continue work with controlled atmosphere,

DPA, as well as several natural antioxidants and formulations that have shown

promise for scald reduction.

PROGRESS: 1994-1998

In 1992, 9 ‘Delicious’ and ‘Granny Smith’ apples, and 9 ‘d’Anjou’ pears were

harvested from 20 moderately to heavily cropped, mature trees located in

commercial orchards near the Tree Fruit Research Laboratory in Wenatchee,

Washington. Pears were harvested on August 18, and ‘Delicious’ and ‘Granny

Smith’ apples on August 31, and September 23, respectively. In the laboratory,

one fruit from each tree was placed on a single tray thereby making 9 trays of

similar fruit. Treatments included an untreated control, farnesene, farnesol,

farnesyl acetate, farnesyl acetone, geraniol, squalene, and wheat germ oil. All

treatments were applied as 100% active material wiped on the fruit and the excess

removed with dry cheesecloth. Fruit were placed in clean trays (plus plastic liners

for pears) and stored in boxes -1C for 6 months (5 months for pears). After

storage fruit were held for 7 days at 22C and evaluated for scald. In addition,

three 2.0-cm plugs were removed symmetrically around the shoulder of each fruit

and the 2-mm epidermal layer extracted with hexane for measurements of

antioxidants (OD200nm), and conjugated trienes (OD258nm) according to

methods previously described. Extracted samples were combined for a single

measurement per fruit. A tray of 20 fruit was also evaluated for maturity at

harvest. Scald development in storage on untreated ‘d’Anjou’ pears was

relatively low during this particular season. Nevertheless, fruit treated with

farnesene, squalene, and wheat germ oil reduced scald from 19% in control fruit

to 2, 1, and 0% respectively. In these treatments, the antioxidant content

(OD200nm) was increased with farnesene, unchanged with squalene and reduced

with wheat germ oil. On the other hand, they all reduced the level of conjugated

trienes (Table 3). Farnesol, farnesyl acetate, farnesyl acetone, and geraniol all

increased scald (or symptoms similar to it) more than 5-fold. The OD200nm in

the peel increased from all these treatments, however, the triene content decreased

in all except those treated with geraniol in which case it increased. (On some fruit

treated with geraniol, the peel was severely damaged resulting in molded and

unusable fruit). In ‘Delicious’ apples, scald after 6 months storage at –1C was

reduced by α-farnesene, farnesol, farnesyl acetate, farnesyl acetone and squalene.

Wheat germ oil had no effect. On the other hand, geraniol completely blackened

the fruit surface, causing severe damage and subsequent infection by various

microorganisms. In all treatments where scald was reduced, the OD200nm

increased. All treatments except farnesol showed higher levels of trienes

(OD258nm). In ‘Granny Smith’, apples scald levels were reduced by all

treatments except geraniol where the fruit surface was completely blackened as

was the case for ‘Delicious’. Farnesol induced the greatest increase whereas

treatment with farnesyl acetate showed the least. Squalene treated fruit had an

incidence of scald equal to 20% of the control. All treatments except wheat germ

oil increased the OD200nm. All treatments except α-farnesene reduced the level

of trienes (OD258nm). Since it was previously reported that the oxidation of α–

farnesene was directly related to the development of scald in both apple and

pears, it was somewhat of a surprise to see the opposite occur. Analysis by gas

chromatography of the farnesene used in this study indicated it was composed of

a mixture of compounds. There was no separation of isomers intended in the

synthesis and it is possible that one of the other compounds had a significant

influence. Another possibility for such complete scald control in pears is that the

farnesene acted more like an oil wipe, reducing the amount of oxygen available

for oxidative reactions, thereby reducing the oxidation of a-farnesene to the

deleterious conjugated trienes. Analysis of squalene, on the other hand, revealed

a single peak. Therefore, if the mode of scald inhibition is not, as previously

suggested, that of reducing the availability of oxygen, it is likely directly

attributable to squalene itself. Another curiosity with respect to previous reports

was the effect of geraniol application. Previous workers injected ‘Granny Smith’

with geraniol and found it reduced scald. Although the peel of fruit we treated

topically was completely darkened, this may have been simply a phytotoxic

reaction to an excessive dose. Clearly, some anomalies warrant further

investigation.

In 1996, 10 ‘Delicious’ and ‘Granny Smith’ apples and 16 ‘d’Anjou’ pears were

harvested from 20 moderately to heavily cropped, mature trees located in

commercial orchards within 10 km of the Tree Fruit Research Laboratory in

Wenatchee, Washington. Pears were harvested on August 29, and ‘Delicious’

apples on September 10. In the laboratory, one fruit from each tree was placed on

a single tray thereby making multiple trays of similar fruit. Treatments included

an untreated control, DPA at 0, 0.05, 0.1 and 0.2%, and ETQ at 0.0675, 0.135 and

0.27% (pears only) with and without 5% squalene plus 0.05% Tween 20. A tray

of 20 fruit was also evaluated for maturity at harvest. All treatments were applied

to fruit 24 hours after harvest by dipping for 1 minute. Fruit were allowed to air

dry for 30 minutes and then placed on clean, dry, fiber trays. Trays (plus plastic

liners for pears) were placed in boxes and stored at -1C for 10 or 6 months for

apples and pears, respectively. After storage, fruit were held for 7 days at 22C

and evaluated for scald. All treatments were replicated 3 times using fruit from

different orchards. After 6 months at -1C plus 7 days at 20C, a 5% emulsion of

squalene reduced scald to 0% on ’d’Anjou’ pears, whereas only at 0.27% did

ETQ achieve the same level of control (Table 7). In ‘Delicious’ apples after 10

months at -1C plus 7 days at 20C, DPA at 0.2% reduced scald to 55%. The

combination of 5% squalene plus 0.2% DPA reduced scald to 7%. Treating with

squalene emulsions showed no phytotoxicity whereas treating with surfactant

alone increased the severity. On apples treated with scald emulsions, scald

evaluations after 10 months showed insufficient control. An evaluation was also

made at 6 months at which time scald control was significantly better (data not

shown). Apparently, in regular storage there is a limit to the efficacy of squalene.

Investigations continue using reduced concentrations of squalene in combination

with other antioxidants as well as with DPA, ETQ, calcium and heat. The other

work on pears was done as an extension of a previous preliminary trial with DPA

in 1995 that indicated a DPA drench of 2000 ppm controlled scald to 25% of the

0-ppm control whereas a 10% squalene emulsion controlled scald 100%. There

was a minor amount of spotting in the DPA trials due to uneven coating and

freestanding drips. In 1996, DPA at 2000 ppm controlled scald to about 13% of

the 0-ppm control and a 5% squalene dip again controlled scald 100%. No

spotting damage was evident In addition, the squalene treatments were more

uniform in color and less ripe. The addition of 5% squalene reduced the amount

of ethoxyquin or DPA necessary to completely control scald to . this amount.

Thus, squalene either alone or in concert with commercial antioxidants improves

scald control and delays fruit ripening. In the last group of experiments, I wanted

to examine the source of DPA injury on ‘d’Anjou’ pears since a number of

countries use this compound, apparently without any deleterious effects. In the

first experiment, DPA was applied to ‘d’Anjou’ pears at the rate of 1000, 2000,

4000, and 8000 ppm. In addition, ETQ at 2700 ppm and 5% squalene in either a

macroemulsion or microemulsion (Dr. Bob Hagenmeier, USDA) were used.

Fruit were allowed to air dry and then placed on trays in plastic liners at -1C.

After 6 months regular storage, evaluations were made for scald as well as surface

DPA injury. Results showed as DPA dose increased, scald decreased. At 4000

ppm DPA was as effective as ETQ at 2700 ppm. At 2000 ppm, scald was reduced

by about 90%. The only chemical injury seen was at 8000 ppm and had the

appearance of darkened patches. At this rate, damage could also have been due to

increased surfactant levels. The microemulsion formulated by Dr. Hagenmeier

controlled scald better than the simple macroemulsion however there was some

skin shrivel associated which we are attempting to eliminate. In a second trial,

fruit were placed in a small, rectangular, plastic container with drainage holes in

the bottom. These fruit were drenched with various rates of DPA and placed

immediately (without drying) in regular or CA storage. After 6 months the total

number of contact points were counted (about 200) and the number of darkened

or damaged lenticels noted. Results indicate when fruit were put in regular

storage while wet there was increasingly more damage to lenticels with increasing

DPA. Mertect alone induced about 9% damage whereas DPA at 2000 and 4000

ppm, caused 16% and 23% damage, respectively. Fruit placed in CA chambers

immediately had almost no damage. Lastly, an ethoxyquin extender was

evaluated for reducing cost of chemicals. Drenching fruit with 2700 ppm ETQ

resulted in 99% scald control. Reducing the rate of ETQ by 50% and adding the

extender reduced scald from 93% to 0%.

PROGRESS: 1998-1999

Because the early maturing ‘Golden Supreme’ apples are harvested before any chilling

hour accumulation, and may be stored for 4 or more months, DPA and MCP were

evaluated for efficacy. For both trials, apples were harvested on 8/20 from the Royal

Slope area. For the DPA trial, fruit were treated with 0, 1000, or 2000 ppm DPA and

stored for 3 or 6 months in regular or CA storage. No Scald was evident at 3 months in

any of the treatments. After 6 months, fruit in CA (2%/2%) had about 3 times the scald

of that in regular storage. In regular storage, 1000 ppm DPA or higher reduced scald to

a score of 1 or less (based on 0=none, 300=worst). Untreated fruit in CA had a scald

score of 204 compared with 35 for fruit treated with 1000 ppm DPA and 4 for fruit

treated with 2000 ppm. At 9 months, only CA fruit remained, of which 75% or more of

all treatments had unacceptable scald ratings. After 3 months, AO levels in regular and

CA control treatments were 72OD and 78OD, respectively. α-Farnesene levels were

5.1OD and 2.2OD respectively. After 9 months, AO and a-farnesene levels for fruit in

CA were 12OD and 10OD respectively.

For the MCP trial, fruit were treated at harvest or 10 weeks after harvest with 1.0 or 0.1

ppm for 1 hour and stored 20 weeks in regular storage. Only the fruit treated at harvest

showed typical MPC behavior of delayed ripening and no scald. Both rates showed

much the same effects with regards to fruit quality and scald. Treating after 10 weeks

showed no effect whether fruit was treated at 0C or 20C. Additional ripening for 10

weeks only induced scald in untreated fruit. MCP treated fruit were still firm and

scald-free.

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