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Stripped corn oil emulsion alters ripening, reduces superficial scald, and reduces core flush in ‘Granny Smith’ apples and decay in ‘d'Anjou’ pears
Postharvest Biology and Technology 20 (2000) 185 – 193 www.elsevier.com/locate/postharvbio
Stripped corn oil emulsion alters ripening, reduces superficial scald, and reduces core flush in ‘Granny Smith’ apples and decay in ‘d’Anjou’ pears Zhiguo Ju *, Eric A. Curry Tree Fruit Research Laboratory, USDA-ARS, 1104 North Western A6enue, Wenatchee, WA 98801, USA Received 7 September 1999; accepted 8 May 2000
Abstract ‘Granny Smith’ apples (Malus x domestica Borkh) and ‘Beurre d’Anjou’ pears (Pyrus communis L.) were dipped in a 2.5, 5, or 10% stripped corn oil (a-tocopherol B 5 mg kg − 1) emulsions, 2000 mg l − 1 diphenylamine (DPA), respectively, at harvest and stored in air at 0°C for 8 months. Untreated fruit served as controls. In oil-treated apples and pears, ethylene and a-farnesene production rates were lower in early storage and higher in late storage than in controls. Untreated ‘Granny Smith’ apples and ‘d’Anjou’ pears developed 34 and 23% superficial scald, respectively, after 6 months storage, whereas fruit treated with oil at 5 or 10%, or with DPA at 2000 mg l − 1 were free from scald. After 8 months storage, oil at 10% was as effective as DPA in controlling scald in pears, whereas in apples, fruit treated with 10% oil developed 18% scald and DPA-treated fruit were scald free. DPA-treated apples, however, developed 32% senescent scald, while 5 or 10% oil-treated fruit had none. Oil-treated fruit were greener, firmer and contained more titratable acidity after 8 months of storage than control or DPA-treated apples and pears. In ‘Granny Smith’, 100% of the controls and 79% of the DPA-treated fruit developed coreflush after 8 months of storage, but in 10% oil-treated fruit, coreflush was eliminated. In ‘d’Anjou’, 34% of the controls and 27% of the DPA-treated fruit showed decay after 8 months of storage, compared with 5% decay in 5% oil-treated fruit, and no decay in 10% oil-treated fruit. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Plant oil; Emulsion; Ethylene; a-Farnesene; Firmness; Storage; Fruit
1. Introduction Diphenylamine (DPA) and ethoxyquin have been used to control superficial scald in apples and pears for many years (Ingle and D’Souza, * Corresponding author. Tel.: +1-509-6642280; fax: +1509-6642287. E-mail address: [email protected] (Z. Ju).
1989; Chen et al., 1990a,b). Increased health concerns from consumers regarding postharvest chemical treatment, as well as pressure from export markets to reduce chemical residue, have caused uncertainty as to the use of these compounds in the future and have hastened the search for alternative approaches to control the disorder. Among the alternatives, traditional oil treatment (Brooks et al., 1919; Huelin and Coggiola, 1968)
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has been reinvestigated in recent years. Wiping ‘‘Granny Smith’ apples with commercial plant oils (canola, caster, palm, peanut, or sunflower) reduced 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’Anjou’ 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-tocopherol ( B5 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 − 1a-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 development 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 treatments 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 senescence, a-farnesene production and scald development, 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 emulsion 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 titratable 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-extraction (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 introduced into each jar and allowed to adsorb volatiles for 10 min. The probe was immediately inserted into the injection port of a gas chromatograph (HP 5890, Hewlett Packard, CA).
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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 N2 carrier, H2 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. Cylindrical 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 epidermis, hypodermis, and several layers of cortical cells) and inner (3 mm thick, mid-section of the flesh) cortical discs. Each treatment included three replications and each replication contained twenty tissue discs. Discs were first washed with 1% (w/v) 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 measured using GC by taking a 0.5-ml air sample from the test tube immediately following a-farnesene measurement.
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 blackening 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 incidence.
2.3. Scald and coreflush e6aluation
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,
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
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 a*/b* 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, Cleveland, OH) and expressed as percent malic acid equivalents.
2.5. Post-storage ethylene treatment on 10% oil-treated fruit
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firmness, SSC, TA, scald, coreflush, internal ethylene 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 regression analysis using SAS Statistical Software (SAS Institute, Cary, NC). Means were separated using Tukey’s Studentized Range Test.
3. Results
3.1. Effects of oil or DPA treatment on a-farnesene and ethylene production In ‘Granny Smith’, ethylene and a-farnesene production in fruit peel were not detectable at harvest, but increased early, and decreased near the end of the storage period (Fig. 1). Both ethylene production and internal ethylene concentration were lower in the 10% oil-treated fruit during the first 3 months of storage and higher after 5 months compared with controls. a-Farnesene production in oil-treated fruit followed the same trend. Effects of oil treatments on ethylene and a-farnesene were concentration dependent. Oil at 5% was less effective than oil at 10%, and oil at 2.5% was ineffective (data not shown). DPA at 2000 mg l − 1 delayed and reduced ethylene and a-farnesene production in early storage but had no effect on internal ethylene compared with controls. In oil-treated fruit, trends of ethylene production in cortical tissue were similar to those in fruit peel (data not shown). In untreated ‘d’Anjou’ pears, ethylene and afarnesene were not detected at harvest or after 1 month storage at 0°C (Fig. 2). After two months storage, both ethylene and a-farnesene increased, reaching a maximum and then decreasing as the storage period ended. Oil at 10% or DPA delayed and reduced ethylene and a-farnesene in early storage. In later storage, however, oil treatment caused an increase in both ethylene and a-farnesene production, while DPA did not. Oil at 5% was less effective than oil at 10%, and oil
at 2.5% did not affect ethylene or a-farnesene production (data not shown).
3.2. Effects of oil or DPA treatment on scald de6elopment after cold storage After 6 months at 0°C plus 7 days at 20°C, untreated ‘Granny Smith’ developed 34% superficial scald (Table 1). Both 5 and 10% oil were as effective as 2000 mg l − 1 DPA in preventing scald development. Oil treatment at 2.5% reduced scald by about one third that of controls. After 8 months, control fruit developed 74% scald. Oil treatments reduced scald in a concentration dependent manner but none of the concentrations used inhibited scald completely. DPA-treated fruit were free from superficial scald. All control fruit and 2.5% oil-treated fruit developed senescent scald. DPA reduced senescent scald to 32%, while fruit treated with 5 or 10% oil were free from senescent scald. Untreated ‘d’Anjou’ pears developed 23% scald after 6 months at 0°C plus 7 days at 20°C (Table 1). Oil at 2.5% was ineffective but at 5 or 10% was as effective as DPA in controlling scald development. After 8 months cold storage plus 7 days at 20°C, control fruit developed 46% scald. Oil at 5% reduced scald by 50%, whereas the 10% oil treatment inhibited scald to the same level as DPA.
3.3. Effects of oil or DPA treatment on other fruit quality attributes after storage Fruit firmness, TA, SSC and green color decreased in untreated ‘d’Anjou’ pears and ‘Granny Smith’ apples after 6 (data not shown) and 8 months of storage at 0°C plus 7 days at 20°C compared with fruit at harvest (Table 2). DPA treatment reduced these changes, but was not as effective as 5 or 10% oil. Effect of oil on these measurements was concentration dependent. All control fruit and 79% of DPA-treated fruit developed core flush in ‘Granny Smith’ apples after 8 months of storage. Oil at 5% reduced, and at 10% completely inhibited core flush. In ‘d’Anjou’
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pears, 30% of untreated fruit developed decay after 8 months of storage. Oil at 10% eliminated decay, but DPA did not (Table 2).
3.4. Effects of post-storage ethylene treatment on qualities of oil-treated fruit When 10% oil-treated ‘Granny Smith’ fruit were held for 8 months at 0°C and then trans-
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ferred to 20°C for 7 days, their internal ethylene concentration and ethylene production rate increased from 16 and 51 mmol kg − 1 s − 1 to 50 and 140 mmol kg − 1 s − 1, respectively. Adding constant 12.5 mmol ethylene at 20°C for 7 days did not change internal ethylene or ethylene production rate in fruit peel. Fruit color, firmness, SSC, TA, scald and coreflush did not change during 7 days in either ethylene-treated or control fruit (data not
Fig. 1. Effects of oil and DPA treatments on internal ethylene, ethylene production, and a-farnesene production in ‘Granny Smith’ apples stored in air at 0°C. Fruit were harvested and treated on 6 October, 1998. HSD, honestly significant difference.
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Fig. 2. Effects of oil and DPA treatments on production of ethylene and a-farnesene in ‘d’Anjou’ pears stored in air at 0°C. Fruit were harvested and treated on 8 September, 1998. HSD, honestly significant difference.
shown). A similar trend was found in ‘d’Anjou’ pears (data not shown).
4. Discussion These results document that oil treatments delayed fruit ripening, maintained other quality attributes in both apples and pears, inhibited or prevented senescent scald and coreflush in apples and reduced decay in pears and confirm the previous report (Ju et al., 2000) that emulsions of edible plant oils are effective superficial scald inhibitors. Although DPA was effective in controlling scald, it was less effective than oil treatments in maintaining fruit firmness, skin color, and acidity as well as in controlling senescent scald, coreflush, and decay. Two of the main disorders that develop in ‘Granny Smith’, namely superficial scald and
coreflush, appear to be related to storage temperature. It has been suggested that superficial scald in ‘Granny Smith’ is related to chilling injury (Watkins et al., 1995). Moreover, core flush in this cultivar is typical of chilling injury (Meheriuk et al., 1994) in that it is more severe at 0°C (Chen et al., 1989; Watkins et al., 1995) than at higher storage temperatures such as 3 or 5°C (Chen et al., 1989). In our study, the high percentage of core flush that developed in control and DPAtreated fruit may, in part, be related to the maturity of the fruit, which were picked 1 week earlier than those for the commercial harvest. Consequently, oil treatment may have great potential in reducing chilling injury-related disorders. Applying oil to fruit inhibited both ethylene and a-farnesene production. Because a-farnesene production is directly related to ethylene biosynthesis during fruit ripening (Ju and Curry, 2000b),
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it is possible that the inhibition of a-farnesene production by oil treatment is through the inhibition of ethylene. However, caution must be taken when interpreting these data since oil applied to fruit peel may absorb a-farnesene and thus reduce a-farnesene evaporation and interfere with the measurement. Therefore, a more accurate analytical method is needed to reaching a conclusion. Because fruit coating with wax or synthesized polymers also reduces ethylene production, respiration, fruit softening, and chlorophyll degradation and has been suggested as a result of modified internal atmosphere including elevated CO2 and reduced O2 (Hagenmaier and Shaw, 1992; Banks et al., 1993; Saftner, 1999), it is possible that a similar mechanism may account
191
for the effects we observed with oil treatment. For example, oil-treated fruit after 8 months storage failed to respond to both internal and external ethylene, indicating ethylene action might be inhibited. However, a more comprehensive study on the modification of internal atmosphere and on the inhibition of ethylene production by oil treatment is needed. Another significant result from oil treatments is the reduction of fruit decay in ‘d’Anjou’ pears. Fruit decay in pears is the most devastating problem to the fruit industry and causes 20% loss each year in packinghouses of the Northwest United States (Kupferman, 1998). Losses are greater in processed fruit because growing, harvesting and storage practices are different than for
Table 1 Effects of stripped corn oil and DPA treatments on superficial scald and senescent scald development in ‘Granny Smith’ apples and ‘d’Anjou’ pears Treatment
6 month
8 month
Superficial scald (%)
Superficial Scald (%)
Senescent Scald (%)
‘Granny Smith’ Control DPA (2000 mg l−1)
34 0
74 0
100 32
Oil 2.5% 5% 10%
21 0 0
67 34 18
100 0 0
Significance Linear Quadratic DPA vs. 10% oil
**** nsa ns
ns
‘d’Anjou’ Control DPA
23 0
46 5
Oil 2.5% 5% 10%
25 0 0
49 24 1
Significance Linear Quadratic DPA vs. 10% oil
ns ns
a
**** **
****
ns, not significant. ** Represents significance at PB0.01. **** Represents significance at PB0.0001.
**** ns ns
**** ns **
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Table 2 Effects of stripped corn oil and DPA treatments on fruit quality in ‘Granny Smith’ apples and ‘Anjou’ pears after 8 months of storage at 0°C and 7 days at 20°C. Treatment
‘Granny Smith’ At harvest DPA (2000 mg l−1) Control Stripped corn oil 2.5% 5% 10%
Firmness (N)
Stripped corn oil 2.5% 5% 10%
TA (% malic acid)
SSC (%)
Core flush or decaya (%)
L
Hue (°)
C*
a/b
87.2 58.9
61.9 65.5
118 112
44.2 44.5
−0.53 −0.40
0.86 0.42
11.2 11.4
79
52.1
64.3
106
43.0
−0.29
0.36
11.2
100
53.4 67.3 73.8
64.1 63.7 63.0
106 111 115
42.7 43.5 44.4
−0.30 −0.39 −0.48
0.36 0.47 0.52
11.2 11.9 12.3
100 11 0
** ns **
**** ns **
**** ns ns
**** ns **
** ns **
* ns **
81.2 31.5
66.1 71.2
114 101
42.9 42.9
−0.44 −0.20
0.42 0.24
12.7 11.0
27
27.5
74.9
101
41.9
−0.19
0.21
10.2
34
26.8 57.2 68.9
75.1 65.4 62.0
100 109 111
42.8 44.3 45.6
−0.18 −0.35 −0.37
0.20 0.31 0.37
10.7 11.8 12.5
41 5 0
** ns **
**** ns **
**** ns **
**** ns **
** ns **
* ns **
ns
Significance Linear **** nsb Quadratic DPA vs. 10% oil **
‘d’Anjou’ At harvest DPA (2000 mg l−1) Control
Fruit color
Significance Linear **** Quadratic ns DPA vs. 10% oil **
**** ns **
**** **
a
Core flush in ‘Granny Smith’; decay in ‘d’Anjou’. ns, not significant. * Represents significance at PB0.01. ** Represents significance at PB0.001. **** Represents significance at PB0.0001.
b
fresh-market fruit (Sholberg, 1998). Certainly, the efficacy and mechanism of oil treatment on reduced fruit decay warrant further investigation. Acknowledgements This research was supported by the Washington State Fruit Tree Research Commission.
References Banks, N.H., Dadzie, B.K., Cleland, D.J., 1993. Reducing gas exchange of fruits with surface coating. Postharvest Biol. Technol. 3, 269 – 284. Brooks, C., Cooley, J.S., Fisher, D.F., 1919. Nature and control of apple scald. J. Agric. Res. 18, 211 – 240. Chen, P.M., Varga, D.M., Mielke, E.A., Drake, S.R., 1989. Poststorage behavior of apple fruit after low oxygen stor-
Z. Ju, E.A. Curry / Posthar6est Biology and Technology 20 (2000) 185–193 age as influenced by temperature during storage and in transit. J. Food Sci. 54, 993–996. Chen, P.M., Varga, D.M., Mielke, E.A., Facteau, T.J., Drake, S.R., 1990a. Control of superficial scald on ‘d’Anjou’ pears by ethoxyquin: effect of ethoxyquin concentration, time and method of application, and a combined effect with controlled atmosphere storage. J. Food Sci. 55, 167–170. Chen, P.M., Varga, D.M., Mielke, E.A., Facteau, T.J., Drake, S.R., 1990b. Control of superficial scald on ‘d’Anjou’ pears by ethoxyquin: oxidation of a-farnesene and its inhibition. J. Food Sci. 55, 171 –175. Curry, E.A., 2000. Farnesene and squalene reduce scald in apples and pears. Acta Hort. 518, 137–144. Hagenmaier, R.D., Shaw, P.E., 1992. Gas permeability of fruit coating waxes. J. Am. Soc. Hort. Sci. 117, 105–109. Huelin, F.E., Coggiola, I.M., 1968. Superficial scald, a functional disorder of stored apples. IV. Effects of variety, oiled wraps, and diphenylamine on concentration of a-farnesene in the fruit. J. Sci. Food Agric. 19, 297–301. Ingle, M., D’Souza, M.C., 1989. Physiology and control of superficial scald of apples: a review. HortScience 24, 28– 31. Ju, Z., Bramlage, W.J., 2000. Cuticular phenolics and scald development in ‘Delicious’ apples. J. Am. Soc. Hort. Sci. 15 (4). Ju, Z., Curry, E.A., 2000a. Lovastatin inhibits a-farnesene synthesis without affecting ethylene production during fruit ripening in ‘Golden Supreme’ apples. J. Am. Soc. Hort. Sci. 125, 105 – 110. Ju, Z., Curry, E.A., 2000b. Evidence that a-farnesene biosynthesis during fruit ripening is mediated by ethylene regulated gene expression in apples. Postharvest Biol. Technol. 19, 9 – 16.
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Ju, Z., Duan, Y., Ju, Z., 2000. Mono-, di-, and tri-acylglycerols and phospholipids from plant oils inhibit scald development in ‘Delicious’ apples. Postharvest Biol. Technol. 19, 1 – 7. Kupferman, E., 1998. Postharvest applied chemicals to pears: a survey of pear packers in Washington, Oregon and California. Tree Fruit Postharvest J. 9, 3 – 24. McGuire, R.G., 1992. Reporting of objective color measurements. HortScience 27, 1254 – 1255. Meheriuk, M., Prange, R.K., Lidster, P.D., Porritt, S.W., 1994. Postharvest disorders of apples and pears. Agric. Can. Pub. 1737/E, 38 – 39. Saftner, R.A., 1999. The potential of fruit coating and film treatments for improving the storage and shelf-life qualities of ‘Gala’ and ‘Golden Delicious’ apples. J. Am. Soc. Hort. Sci. 124, 682 – 689. Scott, K.J., Yuen, C.M.C., Kim, G.H., 1995. Reduction of superficial scald of apples with vegetable oils. Postharvest Biol. Technol. 6, 219 – 223. Sholberg, P.L., 1998. Postharvest strategies that reduce risk of pome fruit decay. 1998 Washington Tree Fruit Postharvest Conference Proceedings, pp. 50 – 54. Watkins, C.B., Barden, C.L., Bramlage, W.J., 1993. Relationships among a-farnesene, conjugated trienes and ethylene production with superficial scald development of apples. Acta Hort. 343, 155 – 160. Watkins, C.B., Bramlage, W.J., Cregoe, B., 1995. Superficial scald of ‘Granny Smith’ apples is expressed as a typical chilling injury. J. Am. Soc. Hort. Sci. 120, 88 – 94. Whitaker, B.D., Solomos, T., Harrison, D.J., 1997. Quantification of a-farnesene and its conjugated trienol oxidation products from apple peel by C18-HPLC with UV detection. J. Agric. Food Chem. 45, 760 – 765.
Stripped corn oil emulsion alters ripening, reduces superficial scald, and reduces core flush in ‘Granny Smith’ apples and decay in ‘d’Anjou’ pears Zhiguo Ju *, Eric A. Curry Tree Fruit Research Laboratory, USDA-ARS, 1104 North Western A6enue, Wenatchee, WA 98801, USA Received 7 September 1999; accepted 8 May 2000
Abstract ‘Granny Smith’ apples (Malus x domestica Borkh) and ‘Beurre d’Anjou’ pears (Pyrus communis L.) were dipped in a 2.5, 5, or 10% stripped corn oil (a-tocopherol B 5 mg kg − 1) emulsions, 2000 mg l − 1 diphenylamine (DPA), respectively, at harvest and stored in air at 0°C for 8 months. Untreated fruit served as controls. In oil-treated apples and pears, ethylene and a-farnesene production rates were lower in early storage and higher in late storage than in controls. Untreated ‘Granny Smith’ apples and ‘d’Anjou’ pears developed 34 and 23% superficial scald, respectively, after 6 months storage, whereas fruit treated with oil at 5 or 10%, or with DPA at 2000 mg l − 1 were free from scald. After 8 months storage, oil at 10% was as effective as DPA in controlling scald in pears, whereas in apples, fruit treated with 10% oil developed 18% scald and DPA-treated fruit were scald free. DPA-treated apples, however, developed 32% senescent scald, while 5 or 10% oil-treated fruit had none. Oil-treated fruit were greener, firmer and contained more titratable acidity after 8 months of storage than control or DPA-treated apples and pears. In ‘Granny Smith’, 100% of the controls and 79% of the DPA-treated fruit developed coreflush after 8 months of storage, but in 10% oil-treated fruit, coreflush was eliminated. In ‘d’Anjou’, 34% of the controls and 27% of the DPA-treated fruit showed decay after 8 months of storage, compared with 5% decay in 5% oil-treated fruit, and no decay in 10% oil-treated fruit. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Plant oil; Emulsion; Ethylene; a-Farnesene; Firmness; Storage; Fruit
1. Introduction Diphenylamine (DPA) and ethoxyquin have been used to control superficial scald in apples and pears for many years (Ingle and D’Souza, * Corresponding author. Tel.: +1-509-6642280; fax: +1509-6642287. E-mail address: [email protected] (Z. Ju).
1989; Chen et al., 1990a,b). Increased health concerns from consumers regarding postharvest chemical treatment, as well as pressure from export markets to reduce chemical residue, have caused uncertainty as to the use of these compounds in the future and have hastened the search for alternative approaches to control the disorder. Among the alternatives, traditional oil treatment (Brooks et al., 1919; Huelin and Coggiola, 1968)
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has been reinvestigated in recent years. Wiping ‘‘Granny Smith’ apples with commercial plant oils (canola, caster, palm, peanut, or sunflower) reduced 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’Anjou’ 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-tocopherol ( B5 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 − 1a-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 development 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 treatments 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 senescence, a-farnesene production and scald development, 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 emulsion 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 titratable 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-extraction (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 introduced into each jar and allowed to adsorb volatiles for 10 min. The probe was immediately inserted into the injection port of a gas chromatograph (HP 5890, Hewlett Packard, CA).
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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 N2 carrier, H2 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. Cylindrical 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 epidermis, hypodermis, and several layers of cortical cells) and inner (3 mm thick, mid-section of the flesh) cortical discs. Each treatment included three replications and each replication contained twenty tissue discs. Discs were first washed with 1% (w/v) 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 measured using GC by taking a 0.5-ml air sample from the test tube immediately following a-farnesene measurement.
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 blackening 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 incidence.
2.3. Scald and coreflush e6aluation
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,
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
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 a*/b* 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, Cleveland, OH) and expressed as percent malic acid equivalents.
2.5. Post-storage ethylene treatment on 10% oil-treated fruit
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firmness, SSC, TA, scald, coreflush, internal ethylene 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 regression analysis using SAS Statistical Software (SAS Institute, Cary, NC). Means were separated using Tukey’s Studentized Range Test.
3. Results
3.1. Effects of oil or DPA treatment on a-farnesene and ethylene production In ‘Granny Smith’, ethylene and a-farnesene production in fruit peel were not detectable at harvest, but increased early, and decreased near the end of the storage period (Fig. 1). Both ethylene production and internal ethylene concentration were lower in the 10% oil-treated fruit during the first 3 months of storage and higher after 5 months compared with controls. a-Farnesene production in oil-treated fruit followed the same trend. Effects of oil treatments on ethylene and a-farnesene were concentration dependent. Oil at 5% was less effective than oil at 10%, and oil at 2.5% was ineffective (data not shown). DPA at 2000 mg l − 1 delayed and reduced ethylene and a-farnesene production in early storage but had no effect on internal ethylene compared with controls. In oil-treated fruit, trends of ethylene production in cortical tissue were similar to those in fruit peel (data not shown). In untreated ‘d’Anjou’ pears, ethylene and afarnesene were not detected at harvest or after 1 month storage at 0°C (Fig. 2). After two months storage, both ethylene and a-farnesene increased, reaching a maximum and then decreasing as the storage period ended. Oil at 10% or DPA delayed and reduced ethylene and a-farnesene in early storage. In later storage, however, oil treatment caused an increase in both ethylene and a-farnesene production, while DPA did not. Oil at 5% was less effective than oil at 10%, and oil
at 2.5% did not affect ethylene or a-farnesene production (data not shown).
3.2. Effects of oil or DPA treatment on scald de6elopment after cold storage After 6 months at 0°C plus 7 days at 20°C, untreated ‘Granny Smith’ developed 34% superficial scald (Table 1). Both 5 and 10% oil were as effective as 2000 mg l − 1 DPA in preventing scald development. Oil treatment at 2.5% reduced scald by about one third that of controls. After 8 months, control fruit developed 74% scald. Oil treatments reduced scald in a concentration dependent manner but none of the concentrations used inhibited scald completely. DPA-treated fruit were free from superficial scald. All control fruit and 2.5% oil-treated fruit developed senescent scald. DPA reduced senescent scald to 32%, while fruit treated with 5 or 10% oil were free from senescent scald. Untreated ‘d’Anjou’ pears developed 23% scald after 6 months at 0°C plus 7 days at 20°C (Table 1). Oil at 2.5% was ineffective but at 5 or 10% was as effective as DPA in controlling scald development. After 8 months cold storage plus 7 days at 20°C, control fruit developed 46% scald. Oil at 5% reduced scald by 50%, whereas the 10% oil treatment inhibited scald to the same level as DPA.
3.3. Effects of oil or DPA treatment on other fruit quality attributes after storage Fruit firmness, TA, SSC and green color decreased in untreated ‘d’Anjou’ pears and ‘Granny Smith’ apples after 6 (data not shown) and 8 months of storage at 0°C plus 7 days at 20°C compared with fruit at harvest (Table 2). DPA treatment reduced these changes, but was not as effective as 5 or 10% oil. Effect of oil on these measurements was concentration dependent. All control fruit and 79% of DPA-treated fruit developed core flush in ‘Granny Smith’ apples after 8 months of storage. Oil at 5% reduced, and at 10% completely inhibited core flush. In ‘d’Anjou’
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pears, 30% of untreated fruit developed decay after 8 months of storage. Oil at 10% eliminated decay, but DPA did not (Table 2).
3.4. Effects of post-storage ethylene treatment on qualities of oil-treated fruit When 10% oil-treated ‘Granny Smith’ fruit were held for 8 months at 0°C and then trans-
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ferred to 20°C for 7 days, their internal ethylene concentration and ethylene production rate increased from 16 and 51 mmol kg − 1 s − 1 to 50 and 140 mmol kg − 1 s − 1, respectively. Adding constant 12.5 mmol ethylene at 20°C for 7 days did not change internal ethylene or ethylene production rate in fruit peel. Fruit color, firmness, SSC, TA, scald and coreflush did not change during 7 days in either ethylene-treated or control fruit (data not
Fig. 1. Effects of oil and DPA treatments on internal ethylene, ethylene production, and a-farnesene production in ‘Granny Smith’ apples stored in air at 0°C. Fruit were harvested and treated on 6 October, 1998. HSD, honestly significant difference.
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Fig. 2. Effects of oil and DPA treatments on production of ethylene and a-farnesene in ‘d’Anjou’ pears stored in air at 0°C. Fruit were harvested and treated on 8 September, 1998. HSD, honestly significant difference.
shown). A similar trend was found in ‘d’Anjou’ pears (data not shown).
4. Discussion These results document that oil treatments delayed fruit ripening, maintained other quality attributes in both apples and pears, inhibited or prevented senescent scald and coreflush in apples and reduced decay in pears and confirm the previous report (Ju et al., 2000) that emulsions of edible plant oils are effective superficial scald inhibitors. Although DPA was effective in controlling scald, it was less effective than oil treatments in maintaining fruit firmness, skin color, and acidity as well as in controlling senescent scald, coreflush, and decay. Two of the main disorders that develop in ‘Granny Smith’, namely superficial scald and
coreflush, appear to be related to storage temperature. It has been suggested that superficial scald in ‘Granny Smith’ is related to chilling injury (Watkins et al., 1995). Moreover, core flush in this cultivar is typical of chilling injury (Meheriuk et al., 1994) in that it is more severe at 0°C (Chen et al., 1989; Watkins et al., 1995) than at higher storage temperatures such as 3 or 5°C (Chen et al., 1989). In our study, the high percentage of core flush that developed in control and DPAtreated fruit may, in part, be related to the maturity of the fruit, which were picked 1 week earlier than those for the commercial harvest. Consequently, oil treatment may have great potential in reducing chilling injury-related disorders. Applying oil to fruit inhibited both ethylene and a-farnesene production. Because a-farnesene production is directly related to ethylene biosynthesis during fruit ripening (Ju and Curry, 2000b),
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it is possible that the inhibition of a-farnesene production by oil treatment is through the inhibition of ethylene. However, caution must be taken when interpreting these data since oil applied to fruit peel may absorb a-farnesene and thus reduce a-farnesene evaporation and interfere with the measurement. Therefore, a more accurate analytical method is needed to reaching a conclusion. Because fruit coating with wax or synthesized polymers also reduces ethylene production, respiration, fruit softening, and chlorophyll degradation and has been suggested as a result of modified internal atmosphere including elevated CO2 and reduced O2 (Hagenmaier and Shaw, 1992; Banks et al., 1993; Saftner, 1999), it is possible that a similar mechanism may account
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for the effects we observed with oil treatment. For example, oil-treated fruit after 8 months storage failed to respond to both internal and external ethylene, indicating ethylene action might be inhibited. However, a more comprehensive study on the modification of internal atmosphere and on the inhibition of ethylene production by oil treatment is needed. Another significant result from oil treatments is the reduction of fruit decay in ‘d’Anjou’ pears. Fruit decay in pears is the most devastating problem to the fruit industry and causes 20% loss each year in packinghouses of the Northwest United States (Kupferman, 1998). Losses are greater in processed fruit because growing, harvesting and storage practices are different than for
Table 1 Effects of stripped corn oil and DPA treatments on superficial scald and senescent scald development in ‘Granny Smith’ apples and ‘d’Anjou’ pears Treatment
6 month
8 month
Superficial scald (%)
Superficial Scald (%)
Senescent Scald (%)
‘Granny Smith’ Control DPA (2000 mg l−1)
34 0
74 0
100 32
Oil 2.5% 5% 10%
21 0 0
67 34 18
100 0 0
Significance Linear Quadratic DPA vs. 10% oil
**** nsa ns
ns
‘d’Anjou’ Control DPA
23 0
46 5
Oil 2.5% 5% 10%
25 0 0
49 24 1
Significance Linear Quadratic DPA vs. 10% oil
ns ns
a
**** **
****
ns, not significant. ** Represents significance at PB0.01. **** Represents significance at PB0.0001.
**** ns ns
**** ns **
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Table 2 Effects of stripped corn oil and DPA treatments on fruit quality in ‘Granny Smith’ apples and ‘Anjou’ pears after 8 months of storage at 0°C and 7 days at 20°C. Treatment
‘Granny Smith’ At harvest DPA (2000 mg l−1) Control Stripped corn oil 2.5% 5% 10%
Firmness (N)
Stripped corn oil 2.5% 5% 10%
TA (% malic acid)
SSC (%)
Core flush or decaya (%)
L
Hue (°)
C*
a/b
87.2 58.9
61.9 65.5
118 112
44.2 44.5
−0.53 −0.40
0.86 0.42
11.2 11.4
79
52.1
64.3
106
43.0
−0.29
0.36
11.2
100
53.4 67.3 73.8
64.1 63.7 63.0
106 111 115
42.7 43.5 44.4
−0.30 −0.39 −0.48
0.36 0.47 0.52
11.2 11.9 12.3
100 11 0
** ns **
**** ns **
**** ns ns
**** ns **
** ns **
* ns **
81.2 31.5
66.1 71.2
114 101
42.9 42.9
−0.44 −0.20
0.42 0.24
12.7 11.0
27
27.5
74.9
101
41.9
−0.19
0.21
10.2
34
26.8 57.2 68.9
75.1 65.4 62.0
100 109 111
42.8 44.3 45.6
−0.18 −0.35 −0.37
0.20 0.31 0.37
10.7 11.8 12.5
41 5 0
** ns **
**** ns **
**** ns **
**** ns **
** ns **
* ns **
ns
Significance Linear **** nsb Quadratic DPA vs. 10% oil **
‘d’Anjou’ At harvest DPA (2000 mg l−1) Control
Fruit color
Significance Linear **** Quadratic ns DPA vs. 10% oil **
**** ns **
**** **
a
Core flush in ‘Granny Smith’; decay in ‘d’Anjou’. ns, not significant. * Represents significance at PB0.01. ** Represents significance at PB0.001. **** Represents significance at PB0.0001.
b
fresh-market fruit (Sholberg, 1998). Certainly, the efficacy and mechanism of oil treatment on reduced fruit decay warrant further investigation. Acknowledgements This research was supported by the Washington State Fruit Tree Research Commission.
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