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Effect of growing season, harvest maturity, waxing, low O2 and elevated CO2 on flesh browning disorders in `Braeburn' apples
Postharvest Biology and Technology 14 (1998) 131 – 141
Effect of growing season, harvest maturity, waxing, low O2 and elevated CO2 on flesh browning disorders in ‘Braeburn’ apples O.L. Lau * Industry Research Program, Okanagan Federated Shippers Association, c/o Agriculture and Agri-Food Canada, Pacific Agri-Food Research Centre, Summerland, BC, V0H 1Z0, Canada Received 10 January 1998; accepted 30 April 1998
Abstract British Columbia-grown ‘Braeburn’ apples (Malus×domestica Borkh.) stored for 6 months in air at 0°C were, on average, 70 N in flesh firmness and had 0.48% titratable acidity. Fruit held in 1.2 or 1.5% O2 + 1.0 or 1.2% CO2 controlled atmosphere (CA) storage were 8 N firmer, 20% higher in titratable acidity, and had significantly less core browning and superficial scald than fruit held in air for the same period. However, CA-stored fruit were highly susceptible to Braeburn browning disorder (BBD) and internal cavities (IC) after cool growing seasons [1993, 1995, and 1996; B1300 degree-days \10°C (DD10) accumulated between May 1 and harvest]. Susceptibility of fruit to BBD and IC was greatest in late-harvested fruit (starch index\2.5 on a 0 – 9 scale) stored in 3.0% CO2 and 1.5% O2. Storage at 1.7, 2.0, 3.0 and 4.0°C did not decrease BBD or IC incidence and tended to increase core browning (1996) and flesh softening (1994 and 1996) compared with fruit kept at 0°C. Coating fruit with Shellac wax, but not Carnauba wax, increased BBD in air-stored fruit. Following a cool growing season it is recommended that ‘Braeburn’ apples be harvested at starch index values between 2.5 and 3.0 and stored in air storage at 0°C to avoid the risks of scald, BBD and IC. The fruit may be stored in B1.0% CO2 (preferably close to 0.1%) and \1.5% O2 after warm seasons ( \ 1300 DD10). © 1998 Elsevier Science B.V. All rights reserved. Keywords: Apple; Braeburn browning disorder; Carbon dioxide injury; Core browning; Firmness; Internal cavity; Low oxygen injury; Preharvest temperature; Postharvest physiology; Scald; Storage disorders
1. Introduction ‘Braeburn’ apples originated as a chance seedling in Nelson, New Zealand, in the early * Fax: + 1 250 4940755; e-mail: [email protected]
1950s. The cultivar has gained wide consumer acceptance because of its distinctive skin color, high dessert quality, and promotion by New Zealand marketers. ‘Braeburn’ has been planted in British Columbia (BC) since 1990. Grower returns for ‘Braeburn’ apples have been two to
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three times greater than for ‘McIntosh’, ‘Golden Delicious’, ‘Spartan’ and ‘Red Delicious’ apples. The erratic browning of flesh and formation of cavities in the fruit limit the storage quality of ‘Braeburn’ apples grown in New Zealand, BC and Washington. These symptoms were first observed in 1978 and given the name ‘Braeburn browning disorder’ (BBD) in 1993 (Elgar et al., 1998). The objective of this research was to quantify the effects of cool growing season, advanced harvest maturity, wax coatings, storage temperature, low O2, and elevated CO2 atmospheres on dessert quality and storage disorders in BC-grown ‘Braeburn’ apples. The information is needed for making planting and replanting decisions, and for developing harvest and storage protocols to maximize dessert quality and minimize storage disorders.
2. Materials and methods
2.1. Effect of prehar6est temperature, har6est maturity, and storage regimes (1993 – 1996) Temperature readings were collected at the Agriculture and Agri-Food Canada weather station, Summerland, BC, and subsequently used for calculating the number of degree-days \ 10°C base temperature (DD10) accumulated between 1 May and harvest. Samples of ‘Braeburn’ apples (Malus ×domestica Borkh.) were harvested four times at weekly intervals (1993–1995) or three times at biweekly intervals (1996) from two (growers A and B in 1993), four (growers A, B, C and D in 1994), six (growers A, B, C, D, E and F in 1995), or five (growers B, C, D, E and F in 1996) commercial orchards in Cawston, Summerland, Naramata and Kelowna, BC. Fruit from each orchard replicate were randomized into ten-fruit samples for maturity determination and 20 – 30-fruit samples for each storage treatment and examination date. Harvesting commenced on 4 October in 1993, 21 September in 1994, 25 September in 1995 and 1 October in 1996, 1–2 weeks before the anticipated commercial harvest.
Percent of skin surfaces with red coloration (by visual estimation), internal ethylene concentration (by gas chromatography), starch index values (by staining transversely cut flesh with I2 –KI solution), flesh firmness (by Magness–Taylor penetrometer with a 11.1-mm diameter tip), titratable acidity (by titration to pH 8.1 with NaOH) and incidence of disorders were determined on each maturity sample immediately after harvest (Lau, 1988). Starch index values of 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9 represent 0, 10, 17, 26, 38, 51, 67, 78, 85 and 99%, respectively, of the cross-sectional area of fruit clear of iodine staining. The storage treatments were: air (0°C; 4 and 6 months) and 1.2% O2 + 1.0% CO2 (0°C; 6 and 8 months) in 1993; air (0°C; 4 and 6 months) and 1.5% O2 + 1.2% CO2 (0, 1.7 and 3.0°C; 6 and 8 months) in 1994; air (0°C; 4 and 6 months) and 1.5% O2 + 1.2% CO2 (0 and 1.7°C; 4, 6 and 8 months) in 1995; and 21% O2 with 0.1, 1.2 or 3.0% CO2 (0°C) and 1.5% O2 with 0.1, 1.2 or 3.0% CO2 (0 and 1.7°C) for 4, 6 and 8 months in 1996. Air storage samples were held in a 0°C room. All CA samples were cooled in 0°C air overnight prior to storage in 1.7 m3 cabinets kept at 0, 1.7 or 3.0°C. The required atmospheres were established within 2 days of sealing by purging with N2 and additions of CO2 and maintained by a computerized CA control system (Techni-System, Chelan, WA). The 0.1% CO2 atmospheres were maintained by placing bags of hydrated lime (50 g kg − 1 of fruit) in the CA chambers. After storage and 7 days in 20°C air, flesh firmness and titratable acidity were determined on ten-fruit samples and incidences of disorders on 20- or 30-fruit samples (Lau, 1983, 1988).
2.2. Effect of storage temperature on late-picked fruit held in air storage (1996) Three replicated boxes (60 apples per box: 20 fruit for harvest measurements and 40 fruit for storage) were picked from each of five commercial orchards in Cawston, Naramata, Summerland and Kelowna, BC, between 22 and 28 October 1996, about 1 week after commercial harvest. After storage for 4.5 months in air at 0, 2 and 4°C plus 7 days in air at 20°C, the fruit were evaluated for quality and incidences of storage disorders.
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2.3. Shellac and Carnauba wax treatments (1996)
3. Results and discussion
Nine replicated fruit samples (30 apples each) were obtained from each of five orchards in Cawston, Naramata, Summerland and Kelowna, BC, between 22 and 28 October in 1996 and held in 0°C air storage. On 13 November, the samples for the wax treatments were coated with Shellac wax (Shield Brite AP-40 from Pace International LP, Kirland, WA) or Carnauba wax (PrimaFresh 30 from S.C. Johnson and Son, Ltd., Brantford, Ont.) at a packinghouse in Oliver, BC. The controls were left untreated. The waxed and nonwaxed samples were subsequently stored in 0°C air for 1, 2 and 3 months, in apple boxes lined with perforated pear plastic liners. This was to determine if the wax treatment, which modified internal gas compositions of fruit (Hagenmaier and Shaw, 1992), would mimic the adverse effect of CA storage on BBD and IC development. Storage quality and incidences of disorders were evaluated on the 30-fruit samples upon removal from the storage and again after 7 days in 20°C.
Starch index values (1993–1996) and percent of surface with red coloration (1994–1996) of the sampled fruit increased, while flesh firmness (1995–1996) and titratable acidity decreased (1995–1996), as harvest occurred later in the season (Table 1). The fruit were susceptible to watercore and had relatively low internal ethylene concentration during the harvest period.
2.4. Fruit density measurements (1996) Three packed cartons of size 88 ‘Braeburn’ apples (7.8–8.0 cm in diameter) were obtained for ten apple cultivars: ‘Braeburn’, ‘Elstar’, ‘Empire’, ‘Fuji’, ‘Gala’, ‘Golden Delicious’, ‘Jonagold’, ‘McIntosh’, ‘Red Delicious’ and ‘Spartan’ at a packing house in Oliver, BC, on 12 November 1996. Fruit density of each apple cultivar was determined on 26 November on nine replicates of 20 fruit each (three replicates per box × 3 boxes) by a water displacement method.
2.5. Statistical analysis (1993 – 1996) Analysis of variance (ANOVA) was performed on storage data to test for main effects and interactions. Percentage values were arcsine square root transformed before variance analysis. Duncan’s new multiple range test was used to separate the treatment means where appropriate.
3.1. Firmness, titratable acidity, core browning and scald after storage ‘Braeburn’ apples stored in air at 0°C for 6 months were on average 70 N in flesh firmness and had 0.48% acids (as malate equivalent; data not shown). Fruit held for 6 months in CA at 0°C were 9 N firmer, were 20% higher in titratable acidity (data not shown), and had significantly less core browning and superficial scald than fruit held in air (Table 2). Incidence of core browning was unrelated to harvest date (Table 2). However, scald incidence was negatively correlated with harvest date (Table 2). The results are in agreement with studies on other cultivars (Lau, 1988, 1997, Ingle and D’Souza, 1989). Harvest date had a strong effect on scald in air-stored fruit, but not in CA-stored fruit, indicating a significant harvest× storage interaction (Table 2).
3.2. Factors affecting BBD and IC ‘Braeburn’ samples had 0, B 3, B 6 and B 2% of the fruit showing browning of the flesh during 1993, 1994, 1995 and 1996 harvests, respectively (Table 1). BBD has occasionally been observed in fruit remaining on the tree late in the season (Curry, 1996, Elgar et al., 1998).
3.2.1. Air 6ersus CA storage Except for the last pick of the 1996 samples (starch index 4.7), the 1993–1996 sampled fruit generally had B 3% BBD after 6 months in air storage (Table 2). The disorder exhibited symptoms fairly typical of those observed with lowtemperature breakdown or low-O2 injury of other apple cultivars (Wilkinson and Fidler, 1973,
0.5 0.4 0.6 2.1 NS 0.2 0.3 0.4 NS
1995 (n= 6) 25 Sep. 2 Oct. 9 Oct. 16 Oct. Significance
1996 (n= 5) 1 Oct. 15 Oct. 28 Oct. Significance
0.8 2.5 4.7 ***
1.7 2.5 3.3 4.2 ***
1.4 2.5 3.2 3.7 **
1.1 2.7 3.6 4.5 *
61 70 74 *
73 78 87 87 ***
69 77 79 83 **
63 79 74 71 NS
Starch index (0– Red skin color 9) (%)
100 96 91 *
96 86 85 81 ***
93 89 85 86 NS
95 90 85 91 NS
Flesh firmness (N)
1993, wet and cool July; 1994, hot July; 1995, cool August; 1996, cool May and September. Significance: NS, non-significant; or significant at * P50.05, ** P50.01 or ***P 50.001.
2.0 4.1 1.0 1.1 NS
1994 (n= 4) 21 Sep. 28 Sep. 5 Oct. 12 Oct. Significance
Internal ethylene concentration (ml l−1) 0.5 0.9 0.4 0.3 NS
Harvest date
1993 (n=2) 4 Oct. 11 Oct. 18 Oct. 25 Oct. Significance
Year
Table 1 Characteristics of ‘Braeburn’ apples from young orchards during 1993–1996 harvest
0.87 0.72 0.80 *
0.85 0.81 0.82 0.79 *
0.76 0.72 0.72 0.72 NS
0.84 0.82 0.76 0.75 NS
Titratable acidity (%)
0 10 32 *
23 19 18 19 NS
7 22 24 12 NS
0 0 0 10 NS
Water core incidence (%)
0 0 2 NS
4 4 6 3 NS
0 0 3 0 NS
0 0 0 0 NS
Braeburn browning incidence (%)
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Table 2 Effect of harvest maturity and storage regime on incidences of Braeburn browning disorder (BBD), internal cavities (IC), core browning (CB) and scald in ‘Braeburn’ apples after 6 months in air or CA a at 0°C, plus 7 days in air at 20°C Year
1993
1994
1995
1996
Harvest date
BBD incidence (%)
IC incidence (%)
CB incidence (%)
Scald incidence (%)
Air
CA
Air
CA
Air
CA
Air
CA
4 Oct. 11 Oct. 18 Oct. 25 Oct. Harvest Storage H×S
0 0 3 0
3 8 8 31
4 2 0 4
10 15 23 21
18 10 14 14
0 3 3 0
38 2 0 0
0 3 3 0
21 Sept. 28 Sept. 5 Oct. 12 Oct. Harvest Storage H×S
0 0 0 0
25 Sept. 2 Oct. 9 Oct. 16 Oct. Harvest Storage H×S
0 1 0 3
1 Oct. 15 Oct. 28 Oct. Harvest Storage H×S
1 0 10
NS ** *
NS * NS 0 0 0 0
0 0 0 0
NS NS NS
NS * NS 0 0 1 7
7 3 6 8
** NS NS 1 9 9 13
3 4 3 3
** ** NS
14 27 23 30
2 2 12
* * NS
1 0 1 1
26 9 0 0
NS NS NS 18 17 14 16
*** *** NS 3 6 33
* * **
*** ** ** 10 11 8 8
26 11 3 1
NS * NS 6 21 24
48 47 37
* ** NS
3 3 0 0 *** *** ***
8 7 5 NS *** NS
0 0 0 0
50 1 0
2 0 0 *** *** ***
a
1.2% O2+1.0% CO2 (1993) or 1.5% O2+1.2% CO2 (1994–1996). Significance: NS, non-significant; significant at * P50.05, ** P50.01 or *** P50.001.
Meheriuk et al., 1994). Wilkinson and Fidler (1973) have stated that it is difficult to distinguish CO2 injury from low temperature breakdown under low levels of CO2 and O2; one difference is that tissue injured by CO2 is much firmer than that subject to low temperature breakdown. In 1993 –1996, the affected tissue was often also afflicted with watercore symptoms. Also, small, elliptical lens-shaped cavities resembling those of internal CO2 injury (Wilkinson and Fidler, 1973, Meheriuk et al., 1994) were found in the flesh or near the core area of B 15% of the late-picked
fruit stored for 4 months in air (Table 2). These cavities are formed when the brown cortical tissues become dehydrated. ‘Braeburn’ apples from New Zealand (Padfield, 1975), WA (Curry, 1996) and Italy (Frasnelli et al., 1996) are susceptible to BBD and IC when stored in CA. Rapid establishment of low O2 atmospheres is commonly recommended for maximizing benefits of CA storage on many apple cultivars (Lau, 1983, 1985, 1997, Little and Peggie, 1987). However, rapid imposition of CA conditions has been found to increase BBD in
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‘Braeburn’ apples (Elgar et al., 1998). In this study, storage of ‘Braeburn’ fruit for 6 months in a 1.2% or 1.5% O2 +1.0% or 1.2% CO2 atmosphere established within 2 – 3 days of harvest increased both BBD and IC relative to air storage after cool (1993, 1995 and 1996) but not warm (1994) growing seasons (Table 2 and Fig. 1). The results indicate that cool seasons followed by rapid storage in elevated CO2 and low O2 increased BBD and IC. Unlike core browning which increased markedly in air-stored fruit after 4 months, development of BBD could occur within a few weeks of storage (data not shown). In susceptible years (e.g. 1995 and 1996), high incidences of BBD and IC were attained in fruit held in CA for 4 months or less (data not shown), and the percentage of affected fruit did not increase thereafter. Results of 8-month samples were similar to those of 6-month samples (Tables 2 and 3) and thus were not included herein.
3.2.2. Temperature during growing season Occurrence of BBD and IC varied greatly with season (Table 2) and orchard (1294% in 1993, 0% in 1994, 89 8% in 1995, and 14 911% in
Fig. 1. Relationship between incidence of Braeburn browning disorder (BBD; after 6 months in 1.2/1.5% O2 + 1.0/1.2% CO2 at 0°C plus 7 days in air at 20°C) in three ‘Braeburn’ apple orchards in Cawston (, 1993–1995), Keremeos (", 1993– 1996) and Summerland (, 1994–1996) and degree-days (10°C base temperature, cumulated between 1 May and harvest). Temperature readings were collected at the Agriculture and Agri-Food Canada weather station, Summerland, BC.
1996; data not shown). BBD symptoms have also occurred erratically in WA- and New Zealandgrown ‘Braeburn’ apples (Curry, 1996, Elgar et al., 1998). In this study, development of BBD in CA-stored fruit from Cawston, Keremeos and Summerland, BC, was closely related to cool growing seasons, i.e. those having B 1300 DD10 (Fig. 1). Likewise in New Zealand, BBD is generally more prevalent in more southern or colder regions, or within colder districts or at higher altitudes within a region (Elgar et al., 1998). Cool growing conditions may alter cellular metabolism, reduce skin and tissue diffusivity and/or increase susceptibility to elevated CO2 and low O2. For example, Park (1990) has shown there is considerable seasonal variability of tissue resistance to gas diffusion. Cool growing seasons have increased the risks of core browning in ‘Cox’s Orange Pippin’ and ‘McIntosh’ and of low temperature breakdown in ‘Bramley’s Seedling’, ‘Cox’s Orange Pippin’, ‘Jonathan’ and ‘Yellow Newton’ apples (Sharples, 1973).
3.2.3. Har6est maturity Susceptibility of ‘Braeburn’ to BBD and IC increased in stored fruit as harvest was delayed in two (1995 and 1996) and three (1994, 1995 and 1996) of the 4 years, respectively (Table 2). The results indicate that BBD was aggravated by advanced maturity, due perhaps to increased respiration rate, increased tissue and skin resistance to gas exchange, and/or increased sensitivity to low O2 and elevated CO2 atmospheres. Meheriuk (1977) has shown more extensive internal CO2 injury in later-picked ‘Golden Delicious’. Park et al. (1993) demonstrated that tissue resistance to gas diffusion in ‘McIntosh’ changed during development and storage. These changes were associated with altered stomatal and lenticular structures. Resistance first increases and then decreases rapidly during the period of fruit maturation, with the highest resistance registered before or on the ethylene climacteric dates (Park et al., 1993). Harvest date had a strong effect on BBD in CA-stored fruit in 1993, but not in air-stored fruit where incidence of the disorder was low. Since the harvest× storage interaction (Table 2) occurred in only 1 of the 4 years, its implication is not clear.
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Table 3 Effect of harvest maturity and storage O2 and CO2 on incidences of Braeburn browning disorder (BBD), internal cavities (IC), core browning (CB) and scald in ‘Braeburn’ apples after 6 months in CA at 0°C, plus 7 days in air at 20°C (1996) Treatment
BBD incidence (%)
IC incidence (%)
CB incidence (%)
Scald incidence (%)
Harvest date 1 Oct. 15 Oct. 28 Oct. Significance
3 13 21 *
12 19 22 NS
29 25 24 NS
34 7 1
Storage O2 21% 1.5% Significance
9 16
11 24 ***
39 13
25 3
Storage CO2 0.1% 1.2% 3.0% Significance
5 10 22
10 10 32
31 22 25
**
***
***
***
*
H×O2 O2×CO2
***
***
11 15 16 NS *** **
Significance: NS, non-significant; significant at * P50.05, ** P50.01, or *** P50.001.
3.2.4. Ele6ated CO2 and low O2 The presence of IC in air-stored fruit with symptoms resembling that of internal CO2 injury, and the large increase of both BBD and IC in late-picked, CA-stored fruit (Table 2) were indicative of an internal accumulation of CO2 and/or depletion of O2 caused by low tissue diffusivity or high skin resistance in ‘Braeburn’ apples. This view was supported by the findings in the 1996 factorial experiment that, at any given harvest date, incidences of BBD and IC were (1) greater in an atmosphere of 1.2% or 3.0% CO2 with 21% O2 than if CO2 was maintained at 0.1% with hydrated lime, and (2) increased by storage in 1.5% O2 (Fig. 2 and Table 3). The results explain why, in 1993, 1995 and 1996, ‘Braeburn’ fruit held in CA were more susceptible to BBD and IC than fruit held in air (Table 2). The results indicate that BBD and IC are CO2-induced disorders and low O2 may aggravate CO2 susceptibility. Kader et al. (1989) and Beaudry and Gran (1993) have found that tolerance to external CO2 generally decreases as external O2 is decreased, while tolerance to low
external O2 decreases as external CO2 is increased. There were no significant harvest date× O2, harvest date× CO2, O2 × CO2 and harvest date× O2 × CO2 interactions for BBD, IC and core browning. However, harvest date× O2 interactions were significant for scald (Table 3), due to a stronger effect of harvest date on scald in airstored fruit than in 1.5% O2-stored fruit (data not shown). Storage CO2 increased scald more readily in air-stored fruit than in CA-stored fruit (data not shown), thus accounting for the significant O2 × CO2 interactions (Table 3).
3.2.5. Wax coating and fruit density Coating fruit with Prolong (Banks, 1984) and NutriSave (Lau and Yastremski, 1991) has altered the natural permeability of fruit skins to gases, resulting in large changes in internal CO2 and O2. In this study, Shellac but not Carnauba wax applied onto late-picked fruit (3.6 starch index, 3% BBD and 29% watercore at harvest) 19 days after harvest increased BBD after 1 month of air storage at 0°C, although the disorder did not
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O.L. Lau / Posthar6est Biology and Technology 14 (1998) 131–141
Fig. 2. Influence of storage CO2, O2 and harvest maturity (starch index) on the incidence of Braeburn browning disorder (BBD) and internal cavities (IC) in ‘Braeburn’ apples after 4.5 months of storage at 0°C and a 7-day shelf-life test in air at 20°C (n = 5 orchards; 1996).
increase further during shelf-life tests or additional time in air storage (Table 4). However, development of IC was unaffected by either wax treatments (data not shown). Hagenmaier and Shaw (1992) have shown that permeability to CO2 and O2 is lower for coatings made from Shellac and rosin than those made from Carnauba and other waxes. Among ten commercial apple cultivars tested, ‘Braeburn’ had the highest fruit density (Table 5). Gas diffusion rates across the cortical tissues of ‘Braeburn’ would, therefore, be lower than those of other cultivars. Rajapakse et al. (1990) have reported that skin resistance of ‘Braeburn’ to O2 diffusion is two and four times higher than those of ‘Granny Smith’ and ‘Cox’s Orange Pippin’,
respectively. Internal O2 under the skin and in the central cavity, intercellular space volume and O2 diffusivity in the flesh are lower for ‘Braeburn’ than for ‘Granny Smith’ and ‘Cox’s Orange Pippin’, and high resistance contributes to susceptibility of ‘Braeburn’ to BBD and IC. Park et al. (1993) has observed that skin discoloration associated with low O2 is positively correlated with fruit resistance to gas diffusion at harvest. Similarly, Johnson et al. (1998) have found association of increased internal CO2 injury with high resistance to gas diffusion. When high resistance apple cultivars such as ‘Braeburn’ are placed in low O2 or elevated CO2 regimes, the internal atmospheres may be modified to a point at which BBD and IC are readily induced.
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Table 4 Effect of postharvest wax treatment on incidence of Braeburn browning disorder (BBD) in late-picked ‘Braeburn’ apples after 1, 2 and 3 months of air storage at 0°C (n= 5 orchards; 1996) Wax treatment
BBD incidence (%) 9Wax, then 0°C air storage for:
Control Carnauba Shellac
Plus 7 days in air at 20°C for:
1 month
2 months
3 months
1 month
2 months
3 months
11 a 15 a 25 b
14 a 24 b 23 ab
11 a 14 ab 28 b
13 a 23 b 37 c
13 a 15 a 30 b
13 a 9a 27 b
Characteristics of fruit at harvest: 3.6 starch index, 97 N firmness, 3% BBD, 29% watercore. After 19 days in 0°C air before waxing: 14% BBD and 15% watercore. Mean separation, within column, by Duncan’s new multiple range test at P50.05.
3.2.6. Storage temperature Storage temperature between 0 and 4.0°C had no significant effect on BBD and IC in ‘Braeburn’ apples held in CA at 0, 1.7 and 3.0°C or in air at 0, 2 and 4°C (data not shown), indicating that BBD and IC are not low-temperature disorders. Similar observations have been made with New Zealand-grown ‘Braeburn’ (Elgar et al., private communication). The use of elevated storage temperatures, however, decreased flesh firmness in CA-stored fruit in two of three seasons (1994 and 1996) and increased core browning in air-stored fruit in 1996 (Table 6). Table 5 Density of ten British Columbia-grown apple cultivars (size 88 apple; 7.8–8.0 cm in diameter; 1996) Apple cultivar ‘Braeburn’ ‘Fuji’ ‘Gala’ ‘Red Delicious’ ‘Jonagold’ ‘Empire’ ‘Elstar’ ‘Spartan’ ‘McIntosh’ ‘Golden Delicious’
Fruit density (kg m−3) 882 g 862 f 841 e 827 d 816 c 815 c 800 b 790 a 788 a 788 a
Means of nine 20-fruit samples (3 packed boxes×3 replicates each) from a packing house in Oliver, BC. Mean separation, within column, by Duncan’s new multiple range test at P5 0.05.
4. Concluding remarks Storage of ‘Braeburn’ apples in 1.2–1.5% O2 + 1.0–1.2% CO2 atmospheres established within 2 to 3 days of harvest improved the retention of flesh firmness and titratable acidity and reduced the incidence of scald and core browning compared to air storage. However, the CA atmospheres markedly increased the incidence of BBD and IC after cool growing seasons especially in fruit picked at a more advanced maturity. Occurrence of these disorders were increased also by Shellac waxing that increases skin resistance to gas diffusion and by storage in elevated CO2 and/or low O2 atmospheres. An ultra-low CO2 (close to 0.1%) and \ 1.5% O2 atmosphere might be acceptable for storage of ‘Braeburn’ apples for 4–6 months after warm growing seasons ( \ 1300 DD10 between 1 May and harvest). A slow or 14-day delay in establishing the CA conditions (Elgar et al., 1998) may be required to reduce the risks of BBD and IC. After a cool growing season, however, the fruit were best held in ventilated air storage for not more than 4 months to reduce the risks of CO2- and low O2-induced BBD and IC. It would be interesting to determine the biochemical basis of BBD and IC development and whether these disorders can be predicted based on preharvest orchard temperature and internal CO2 and O2. The benefit of pre-CA delays in 0°C air also needs to be ascertained for the control of BBD in BC-grown ‘Braeburn’ apples.
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Table 6 Effect of storage temperature on flesh firmness and core browning (CB) in ‘Braeburn’ apples held in CA or air Year
Storage
Duration (months)
Temperature (°C)
Firmness (N)
CB incidence (%)
1994
CA
6
0 1.7 3.0 Significance
76 70 67 **
1 0 2 NS
1995
CA
6
0 1.7 Significance
81 78 NS
9 5 NS
1996
CA
6
0 1.7 Significance
83 81 **
13 15 NS
Air
4
0 2.0 4.0 Significance
76 63 60 ***
8 13 34 ***
1994–1995, 1.5% O2+1.2% CO2; 1996, 1.5% O2+0.1 to 3.0% CO2. Characteristics of fruit at harvest: 218 g per fruit, 3.6 starch index, 97 N firmness, 3% BBD, 29% watercore. Significance: NS, non-significant; significant at * P50.05, ** P50.01, *** P50.001.
Acknowledgements This work was not possible without the technical assistance of R. Yastremski, P. Schofield, W. Urban and S. Horton, and the financial support of the Okanagan Valley Tree Fruit Authority.
References Banks, N.H., 1984. Internal atmosphere modification in Prolong coated apples. Acta Hortic. 157, 105–112. Beaudry, R.M., Gran, C.D., 1993. Using a modified-atmosphere packing approach to answer some post-harvest questions: factors influencing the lower oxygen limit. Acta Hortic. 326, 203 – 212. Curry, E.C., 1996. Maintaining optimum fruit quality of ‘Braeburn’ apples. Wash. State Univ. Tree Fruit Postharvest J. 7 (1), 3 – 7. Elgar, H.J., Burmeister, D.M., Watkins, C.B., 1998. Storage and handling effects on a CO2-related internal browning disorder of ‘Braeburn’ apples. HortScience 33 (4), 719– 722. Frasnelli. K., Casera, C., de Jager, A. (Ed.), Johnson, D. (Ed.), Hohn, E., 1996. Influence of harvest date on fruit quality and storability in the varieties Braeburn and Gala. COST 94. The postharvest treatment of fruit and vegetables. Determination and prediction of optimum harvest
date of apples and pears. Proceedings of a Meeting, Lofthus, Norway, 9 – 10 June 1994, pp. 105 – 115. Hagenmaier, R.D., Shaw, P.E., 1992. Gas permeability of fruit coating waxes. J. Am. Soc. Hortic. Sci. 117 (1), 105 – 109. Ingle, M., D’Souza, M.C., 1989. Physiology and control of superficial scald of apples: a review. HortScience 24 (1), 28 – 31. Johnson, D.S., Dover, C.J., Colgan, R.J., 1998. Effect of rate of establishment of CA conditions on the development of ‘CO2 injury’ in Bramley’s Seedling apples. Acta Hortic. 464, 351 – 356. Kader, A.A., Zagory, D., Kebel, E.L., 1989. Modified atmosphere packaging of fruits and vegetables. Crit. Rev. Food Sci. Nutr. 28 (6), 1 – 30. Lau, O.L., 1983. Effects of storage procedures and low oxygen and carbon dioxide atmospheres on storage quality of ‘Spartan’ apples. J. Am. Soc. Hortic. Sci. 108 (2), 953 – 957. Lau, O.L., 1985. Storage procedures, low oxygen, and low carbon dioxide atmospheres on storage quality of ‘Golden Delicious’ and ‘Delicious’ apples. J. Am. Soc. Hortic. Sci. 110 (4), 541 – 547. Lau, O.L., 1988. Harvest indices, dessert quality, and storability of ‘Jonagold’ apples in air and controlled atmosphere storage. J. Am. Soc. Hortic. Sci. 113 (4), 564 – 569. Lau, O.L., 1997. The effectiveness of 0.7% O2 to attenuate scald symptoms in ‘Delicious’ apples is influenced by harvest maturity and cultivar strain. J. Am. Soc. Hortic. Sci. 122 (5), 691 – 697. Lau, O.L., Yastremski, R., 1991. Retention of quality of ‘Golden Delicious’ apples by controlled- and modified-atmosphere storage. HortScience 26 (5), 564 – 566.
O.L. Lau / Posthar6est Biology and Technology 14 (1998) 131–141 Little, C.R., Peggie, I.D., 1987. Storage injury of pome fruit caused by stress levels of oxygen, carbon dioxide, temperature and ethylene. HortScience 22 (5), 783–790. Meheriuk, M., 1977. Treatment of Golden Delicious apples with CO2 prior to CA storage. Can. J. Plant Sci. 57 (2), 467 – 471. Meheriuk, M., Prange, R.K., Lidster, P.D., Porritt, S.W., 1994. Postharvest disorders of apples and pears. Agriculture Canada Publication 1737/E. Communications Branch, Agriculture Canada, Ottawa, pp. 18–21, 24–27. Padfield, C.A.S., 1975. Storage conditions for some of the more recently introduced apple cultivars. Orchardist New Zealand 48, 64. Park, Y.M., 1990. Gas exchange in apples: pathway for gas exchange, changes in resistance to gas diffusion during development and storage, and factors affecting the changes. Ph.D. Dissertation, Cornell University, Ithaca, NY, 116 pp. Park, Y.M., Blanpied, G.D., Jozwiak, Z., Liu, F.W., 1993. Postharvest studies of resistance to gas diffusion in
.
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McIntosh apples. Postharvest Biol. Technol. 2 (4), 329 – 339. Rajapakse, N.C., Banks, N.H., Hewett, E.W., Cleland, D.J., 1990. Development of oxygen concentration gradients in flesh tissues of bulky plant organs. J. Am. Soc. Hortic. Sci. 115 (5), 793 – 797. Sharples, R.O., 1973. Climatic effects. In: Fidler, J.C., Wilkinson, B.G., Edney, K.L., Sharples, R.O. (Eds.), The Biology of Apple and Pear Storage. Part Four. Orchard and Climatic Factors. Research Review No. 3, Commonwealth Bureau of Horticulture and Plantation Crops, East Malling, pp. 204 – 208. Wilkinson, K.L., Fidler, J.C., 1973. Injuries caused by incorrect concentrations of carbon dioxide and/or oxygen. In: Fidler, J.C., Wilkinson, B.G., Edney, K.L., Sharples, R.O. (Eds.), The Biology of Apple and Pear Storage. Part Two. Physiological Disorders. Research Review No. 3, Commonwealth Bureau of Horticulture and Plantation Crops, East Malling, pp. 81 – 87.
Effect of growing season, harvest maturity, waxing, low O2 and elevated CO2 on flesh browning disorders in ‘Braeburn’ apples O.L. Lau * Industry Research Program, Okanagan Federated Shippers Association, c/o Agriculture and Agri-Food Canada, Pacific Agri-Food Research Centre, Summerland, BC, V0H 1Z0, Canada Received 10 January 1998; accepted 30 April 1998
Abstract British Columbia-grown ‘Braeburn’ apples (Malus×domestica Borkh.) stored for 6 months in air at 0°C were, on average, 70 N in flesh firmness and had 0.48% titratable acidity. Fruit held in 1.2 or 1.5% O2 + 1.0 or 1.2% CO2 controlled atmosphere (CA) storage were 8 N firmer, 20% higher in titratable acidity, and had significantly less core browning and superficial scald than fruit held in air for the same period. However, CA-stored fruit were highly susceptible to Braeburn browning disorder (BBD) and internal cavities (IC) after cool growing seasons [1993, 1995, and 1996; B1300 degree-days \10°C (DD10) accumulated between May 1 and harvest]. Susceptibility of fruit to BBD and IC was greatest in late-harvested fruit (starch index\2.5 on a 0 – 9 scale) stored in 3.0% CO2 and 1.5% O2. Storage at 1.7, 2.0, 3.0 and 4.0°C did not decrease BBD or IC incidence and tended to increase core browning (1996) and flesh softening (1994 and 1996) compared with fruit kept at 0°C. Coating fruit with Shellac wax, but not Carnauba wax, increased BBD in air-stored fruit. Following a cool growing season it is recommended that ‘Braeburn’ apples be harvested at starch index values between 2.5 and 3.0 and stored in air storage at 0°C to avoid the risks of scald, BBD and IC. The fruit may be stored in B1.0% CO2 (preferably close to 0.1%) and \1.5% O2 after warm seasons ( \ 1300 DD10). © 1998 Elsevier Science B.V. All rights reserved. Keywords: Apple; Braeburn browning disorder; Carbon dioxide injury; Core browning; Firmness; Internal cavity; Low oxygen injury; Preharvest temperature; Postharvest physiology; Scald; Storage disorders
1. Introduction ‘Braeburn’ apples originated as a chance seedling in Nelson, New Zealand, in the early * Fax: + 1 250 4940755; e-mail: [email protected]
1950s. The cultivar has gained wide consumer acceptance because of its distinctive skin color, high dessert quality, and promotion by New Zealand marketers. ‘Braeburn’ has been planted in British Columbia (BC) since 1990. Grower returns for ‘Braeburn’ apples have been two to
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three times greater than for ‘McIntosh’, ‘Golden Delicious’, ‘Spartan’ and ‘Red Delicious’ apples. The erratic browning of flesh and formation of cavities in the fruit limit the storage quality of ‘Braeburn’ apples grown in New Zealand, BC and Washington. These symptoms were first observed in 1978 and given the name ‘Braeburn browning disorder’ (BBD) in 1993 (Elgar et al., 1998). The objective of this research was to quantify the effects of cool growing season, advanced harvest maturity, wax coatings, storage temperature, low O2, and elevated CO2 atmospheres on dessert quality and storage disorders in BC-grown ‘Braeburn’ apples. The information is needed for making planting and replanting decisions, and for developing harvest and storage protocols to maximize dessert quality and minimize storage disorders.
2. Materials and methods
2.1. Effect of prehar6est temperature, har6est maturity, and storage regimes (1993 – 1996) Temperature readings were collected at the Agriculture and Agri-Food Canada weather station, Summerland, BC, and subsequently used for calculating the number of degree-days \ 10°C base temperature (DD10) accumulated between 1 May and harvest. Samples of ‘Braeburn’ apples (Malus ×domestica Borkh.) were harvested four times at weekly intervals (1993–1995) or three times at biweekly intervals (1996) from two (growers A and B in 1993), four (growers A, B, C and D in 1994), six (growers A, B, C, D, E and F in 1995), or five (growers B, C, D, E and F in 1996) commercial orchards in Cawston, Summerland, Naramata and Kelowna, BC. Fruit from each orchard replicate were randomized into ten-fruit samples for maturity determination and 20 – 30-fruit samples for each storage treatment and examination date. Harvesting commenced on 4 October in 1993, 21 September in 1994, 25 September in 1995 and 1 October in 1996, 1–2 weeks before the anticipated commercial harvest.
Percent of skin surfaces with red coloration (by visual estimation), internal ethylene concentration (by gas chromatography), starch index values (by staining transversely cut flesh with I2 –KI solution), flesh firmness (by Magness–Taylor penetrometer with a 11.1-mm diameter tip), titratable acidity (by titration to pH 8.1 with NaOH) and incidence of disorders were determined on each maturity sample immediately after harvest (Lau, 1988). Starch index values of 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9 represent 0, 10, 17, 26, 38, 51, 67, 78, 85 and 99%, respectively, of the cross-sectional area of fruit clear of iodine staining. The storage treatments were: air (0°C; 4 and 6 months) and 1.2% O2 + 1.0% CO2 (0°C; 6 and 8 months) in 1993; air (0°C; 4 and 6 months) and 1.5% O2 + 1.2% CO2 (0, 1.7 and 3.0°C; 6 and 8 months) in 1994; air (0°C; 4 and 6 months) and 1.5% O2 + 1.2% CO2 (0 and 1.7°C; 4, 6 and 8 months) in 1995; and 21% O2 with 0.1, 1.2 or 3.0% CO2 (0°C) and 1.5% O2 with 0.1, 1.2 or 3.0% CO2 (0 and 1.7°C) for 4, 6 and 8 months in 1996. Air storage samples were held in a 0°C room. All CA samples were cooled in 0°C air overnight prior to storage in 1.7 m3 cabinets kept at 0, 1.7 or 3.0°C. The required atmospheres were established within 2 days of sealing by purging with N2 and additions of CO2 and maintained by a computerized CA control system (Techni-System, Chelan, WA). The 0.1% CO2 atmospheres were maintained by placing bags of hydrated lime (50 g kg − 1 of fruit) in the CA chambers. After storage and 7 days in 20°C air, flesh firmness and titratable acidity were determined on ten-fruit samples and incidences of disorders on 20- or 30-fruit samples (Lau, 1983, 1988).
2.2. Effect of storage temperature on late-picked fruit held in air storage (1996) Three replicated boxes (60 apples per box: 20 fruit for harvest measurements and 40 fruit for storage) were picked from each of five commercial orchards in Cawston, Naramata, Summerland and Kelowna, BC, between 22 and 28 October 1996, about 1 week after commercial harvest. After storage for 4.5 months in air at 0, 2 and 4°C plus 7 days in air at 20°C, the fruit were evaluated for quality and incidences of storage disorders.
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2.3. Shellac and Carnauba wax treatments (1996)
3. Results and discussion
Nine replicated fruit samples (30 apples each) were obtained from each of five orchards in Cawston, Naramata, Summerland and Kelowna, BC, between 22 and 28 October in 1996 and held in 0°C air storage. On 13 November, the samples for the wax treatments were coated with Shellac wax (Shield Brite AP-40 from Pace International LP, Kirland, WA) or Carnauba wax (PrimaFresh 30 from S.C. Johnson and Son, Ltd., Brantford, Ont.) at a packinghouse in Oliver, BC. The controls were left untreated. The waxed and nonwaxed samples were subsequently stored in 0°C air for 1, 2 and 3 months, in apple boxes lined with perforated pear plastic liners. This was to determine if the wax treatment, which modified internal gas compositions of fruit (Hagenmaier and Shaw, 1992), would mimic the adverse effect of CA storage on BBD and IC development. Storage quality and incidences of disorders were evaluated on the 30-fruit samples upon removal from the storage and again after 7 days in 20°C.
Starch index values (1993–1996) and percent of surface with red coloration (1994–1996) of the sampled fruit increased, while flesh firmness (1995–1996) and titratable acidity decreased (1995–1996), as harvest occurred later in the season (Table 1). The fruit were susceptible to watercore and had relatively low internal ethylene concentration during the harvest period.
2.4. Fruit density measurements (1996) Three packed cartons of size 88 ‘Braeburn’ apples (7.8–8.0 cm in diameter) were obtained for ten apple cultivars: ‘Braeburn’, ‘Elstar’, ‘Empire’, ‘Fuji’, ‘Gala’, ‘Golden Delicious’, ‘Jonagold’, ‘McIntosh’, ‘Red Delicious’ and ‘Spartan’ at a packing house in Oliver, BC, on 12 November 1996. Fruit density of each apple cultivar was determined on 26 November on nine replicates of 20 fruit each (three replicates per box × 3 boxes) by a water displacement method.
2.5. Statistical analysis (1993 – 1996) Analysis of variance (ANOVA) was performed on storage data to test for main effects and interactions. Percentage values were arcsine square root transformed before variance analysis. Duncan’s new multiple range test was used to separate the treatment means where appropriate.
3.1. Firmness, titratable acidity, core browning and scald after storage ‘Braeburn’ apples stored in air at 0°C for 6 months were on average 70 N in flesh firmness and had 0.48% acids (as malate equivalent; data not shown). Fruit held for 6 months in CA at 0°C were 9 N firmer, were 20% higher in titratable acidity (data not shown), and had significantly less core browning and superficial scald than fruit held in air (Table 2). Incidence of core browning was unrelated to harvest date (Table 2). However, scald incidence was negatively correlated with harvest date (Table 2). The results are in agreement with studies on other cultivars (Lau, 1988, 1997, Ingle and D’Souza, 1989). Harvest date had a strong effect on scald in air-stored fruit, but not in CA-stored fruit, indicating a significant harvest× storage interaction (Table 2).
3.2. Factors affecting BBD and IC ‘Braeburn’ samples had 0, B 3, B 6 and B 2% of the fruit showing browning of the flesh during 1993, 1994, 1995 and 1996 harvests, respectively (Table 1). BBD has occasionally been observed in fruit remaining on the tree late in the season (Curry, 1996, Elgar et al., 1998).
3.2.1. Air 6ersus CA storage Except for the last pick of the 1996 samples (starch index 4.7), the 1993–1996 sampled fruit generally had B 3% BBD after 6 months in air storage (Table 2). The disorder exhibited symptoms fairly typical of those observed with lowtemperature breakdown or low-O2 injury of other apple cultivars (Wilkinson and Fidler, 1973,
0.5 0.4 0.6 2.1 NS 0.2 0.3 0.4 NS
1995 (n= 6) 25 Sep. 2 Oct. 9 Oct. 16 Oct. Significance
1996 (n= 5) 1 Oct. 15 Oct. 28 Oct. Significance
0.8 2.5 4.7 ***
1.7 2.5 3.3 4.2 ***
1.4 2.5 3.2 3.7 **
1.1 2.7 3.6 4.5 *
61 70 74 *
73 78 87 87 ***
69 77 79 83 **
63 79 74 71 NS
Starch index (0– Red skin color 9) (%)
100 96 91 *
96 86 85 81 ***
93 89 85 86 NS
95 90 85 91 NS
Flesh firmness (N)
1993, wet and cool July; 1994, hot July; 1995, cool August; 1996, cool May and September. Significance: NS, non-significant; or significant at * P50.05, ** P50.01 or ***P 50.001.
2.0 4.1 1.0 1.1 NS
1994 (n= 4) 21 Sep. 28 Sep. 5 Oct. 12 Oct. Significance
Internal ethylene concentration (ml l−1) 0.5 0.9 0.4 0.3 NS
Harvest date
1993 (n=2) 4 Oct. 11 Oct. 18 Oct. 25 Oct. Significance
Year
Table 1 Characteristics of ‘Braeburn’ apples from young orchards during 1993–1996 harvest
0.87 0.72 0.80 *
0.85 0.81 0.82 0.79 *
0.76 0.72 0.72 0.72 NS
0.84 0.82 0.76 0.75 NS
Titratable acidity (%)
0 10 32 *
23 19 18 19 NS
7 22 24 12 NS
0 0 0 10 NS
Water core incidence (%)
0 0 2 NS
4 4 6 3 NS
0 0 3 0 NS
0 0 0 0 NS
Braeburn browning incidence (%)
134 O.L. Lau / Posthar6est Biology and Technology 14 (1998) 131–141
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Table 2 Effect of harvest maturity and storage regime on incidences of Braeburn browning disorder (BBD), internal cavities (IC), core browning (CB) and scald in ‘Braeburn’ apples after 6 months in air or CA a at 0°C, plus 7 days in air at 20°C Year
1993
1994
1995
1996
Harvest date
BBD incidence (%)
IC incidence (%)
CB incidence (%)
Scald incidence (%)
Air
CA
Air
CA
Air
CA
Air
CA
4 Oct. 11 Oct. 18 Oct. 25 Oct. Harvest Storage H×S
0 0 3 0
3 8 8 31
4 2 0 4
10 15 23 21
18 10 14 14
0 3 3 0
38 2 0 0
0 3 3 0
21 Sept. 28 Sept. 5 Oct. 12 Oct. Harvest Storage H×S
0 0 0 0
25 Sept. 2 Oct. 9 Oct. 16 Oct. Harvest Storage H×S
0 1 0 3
1 Oct. 15 Oct. 28 Oct. Harvest Storage H×S
1 0 10
NS ** *
NS * NS 0 0 0 0
0 0 0 0
NS NS NS
NS * NS 0 0 1 7
7 3 6 8
** NS NS 1 9 9 13
3 4 3 3
** ** NS
14 27 23 30
2 2 12
* * NS
1 0 1 1
26 9 0 0
NS NS NS 18 17 14 16
*** *** NS 3 6 33
* * **
*** ** ** 10 11 8 8
26 11 3 1
NS * NS 6 21 24
48 47 37
* ** NS
3 3 0 0 *** *** ***
8 7 5 NS *** NS
0 0 0 0
50 1 0
2 0 0 *** *** ***
a
1.2% O2+1.0% CO2 (1993) or 1.5% O2+1.2% CO2 (1994–1996). Significance: NS, non-significant; significant at * P50.05, ** P50.01 or *** P50.001.
Meheriuk et al., 1994). Wilkinson and Fidler (1973) have stated that it is difficult to distinguish CO2 injury from low temperature breakdown under low levels of CO2 and O2; one difference is that tissue injured by CO2 is much firmer than that subject to low temperature breakdown. In 1993 –1996, the affected tissue was often also afflicted with watercore symptoms. Also, small, elliptical lens-shaped cavities resembling those of internal CO2 injury (Wilkinson and Fidler, 1973, Meheriuk et al., 1994) were found in the flesh or near the core area of B 15% of the late-picked
fruit stored for 4 months in air (Table 2). These cavities are formed when the brown cortical tissues become dehydrated. ‘Braeburn’ apples from New Zealand (Padfield, 1975), WA (Curry, 1996) and Italy (Frasnelli et al., 1996) are susceptible to BBD and IC when stored in CA. Rapid establishment of low O2 atmospheres is commonly recommended for maximizing benefits of CA storage on many apple cultivars (Lau, 1983, 1985, 1997, Little and Peggie, 1987). However, rapid imposition of CA conditions has been found to increase BBD in
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‘Braeburn’ apples (Elgar et al., 1998). In this study, storage of ‘Braeburn’ fruit for 6 months in a 1.2% or 1.5% O2 +1.0% or 1.2% CO2 atmosphere established within 2 – 3 days of harvest increased both BBD and IC relative to air storage after cool (1993, 1995 and 1996) but not warm (1994) growing seasons (Table 2 and Fig. 1). The results indicate that cool seasons followed by rapid storage in elevated CO2 and low O2 increased BBD and IC. Unlike core browning which increased markedly in air-stored fruit after 4 months, development of BBD could occur within a few weeks of storage (data not shown). In susceptible years (e.g. 1995 and 1996), high incidences of BBD and IC were attained in fruit held in CA for 4 months or less (data not shown), and the percentage of affected fruit did not increase thereafter. Results of 8-month samples were similar to those of 6-month samples (Tables 2 and 3) and thus were not included herein.
3.2.2. Temperature during growing season Occurrence of BBD and IC varied greatly with season (Table 2) and orchard (1294% in 1993, 0% in 1994, 89 8% in 1995, and 14 911% in
Fig. 1. Relationship between incidence of Braeburn browning disorder (BBD; after 6 months in 1.2/1.5% O2 + 1.0/1.2% CO2 at 0°C plus 7 days in air at 20°C) in three ‘Braeburn’ apple orchards in Cawston (, 1993–1995), Keremeos (", 1993– 1996) and Summerland (, 1994–1996) and degree-days (10°C base temperature, cumulated between 1 May and harvest). Temperature readings were collected at the Agriculture and Agri-Food Canada weather station, Summerland, BC.
1996; data not shown). BBD symptoms have also occurred erratically in WA- and New Zealandgrown ‘Braeburn’ apples (Curry, 1996, Elgar et al., 1998). In this study, development of BBD in CA-stored fruit from Cawston, Keremeos and Summerland, BC, was closely related to cool growing seasons, i.e. those having B 1300 DD10 (Fig. 1). Likewise in New Zealand, BBD is generally more prevalent in more southern or colder regions, or within colder districts or at higher altitudes within a region (Elgar et al., 1998). Cool growing conditions may alter cellular metabolism, reduce skin and tissue diffusivity and/or increase susceptibility to elevated CO2 and low O2. For example, Park (1990) has shown there is considerable seasonal variability of tissue resistance to gas diffusion. Cool growing seasons have increased the risks of core browning in ‘Cox’s Orange Pippin’ and ‘McIntosh’ and of low temperature breakdown in ‘Bramley’s Seedling’, ‘Cox’s Orange Pippin’, ‘Jonathan’ and ‘Yellow Newton’ apples (Sharples, 1973).
3.2.3. Har6est maturity Susceptibility of ‘Braeburn’ to BBD and IC increased in stored fruit as harvest was delayed in two (1995 and 1996) and three (1994, 1995 and 1996) of the 4 years, respectively (Table 2). The results indicate that BBD was aggravated by advanced maturity, due perhaps to increased respiration rate, increased tissue and skin resistance to gas exchange, and/or increased sensitivity to low O2 and elevated CO2 atmospheres. Meheriuk (1977) has shown more extensive internal CO2 injury in later-picked ‘Golden Delicious’. Park et al. (1993) demonstrated that tissue resistance to gas diffusion in ‘McIntosh’ changed during development and storage. These changes were associated with altered stomatal and lenticular structures. Resistance first increases and then decreases rapidly during the period of fruit maturation, with the highest resistance registered before or on the ethylene climacteric dates (Park et al., 1993). Harvest date had a strong effect on BBD in CA-stored fruit in 1993, but not in air-stored fruit where incidence of the disorder was low. Since the harvest× storage interaction (Table 2) occurred in only 1 of the 4 years, its implication is not clear.
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Table 3 Effect of harvest maturity and storage O2 and CO2 on incidences of Braeburn browning disorder (BBD), internal cavities (IC), core browning (CB) and scald in ‘Braeburn’ apples after 6 months in CA at 0°C, plus 7 days in air at 20°C (1996) Treatment
BBD incidence (%)
IC incidence (%)
CB incidence (%)
Scald incidence (%)
Harvest date 1 Oct. 15 Oct. 28 Oct. Significance
3 13 21 *
12 19 22 NS
29 25 24 NS
34 7 1
Storage O2 21% 1.5% Significance
9 16
11 24 ***
39 13
25 3
Storage CO2 0.1% 1.2% 3.0% Significance
5 10 22
10 10 32
31 22 25
**
***
***
***
*
H×O2 O2×CO2
***
***
11 15 16 NS *** **
Significance: NS, non-significant; significant at * P50.05, ** P50.01, or *** P50.001.
3.2.4. Ele6ated CO2 and low O2 The presence of IC in air-stored fruit with symptoms resembling that of internal CO2 injury, and the large increase of both BBD and IC in late-picked, CA-stored fruit (Table 2) were indicative of an internal accumulation of CO2 and/or depletion of O2 caused by low tissue diffusivity or high skin resistance in ‘Braeburn’ apples. This view was supported by the findings in the 1996 factorial experiment that, at any given harvest date, incidences of BBD and IC were (1) greater in an atmosphere of 1.2% or 3.0% CO2 with 21% O2 than if CO2 was maintained at 0.1% with hydrated lime, and (2) increased by storage in 1.5% O2 (Fig. 2 and Table 3). The results explain why, in 1993, 1995 and 1996, ‘Braeburn’ fruit held in CA were more susceptible to BBD and IC than fruit held in air (Table 2). The results indicate that BBD and IC are CO2-induced disorders and low O2 may aggravate CO2 susceptibility. Kader et al. (1989) and Beaudry and Gran (1993) have found that tolerance to external CO2 generally decreases as external O2 is decreased, while tolerance to low
external O2 decreases as external CO2 is increased. There were no significant harvest date× O2, harvest date× CO2, O2 × CO2 and harvest date× O2 × CO2 interactions for BBD, IC and core browning. However, harvest date× O2 interactions were significant for scald (Table 3), due to a stronger effect of harvest date on scald in airstored fruit than in 1.5% O2-stored fruit (data not shown). Storage CO2 increased scald more readily in air-stored fruit than in CA-stored fruit (data not shown), thus accounting for the significant O2 × CO2 interactions (Table 3).
3.2.5. Wax coating and fruit density Coating fruit with Prolong (Banks, 1984) and NutriSave (Lau and Yastremski, 1991) has altered the natural permeability of fruit skins to gases, resulting in large changes in internal CO2 and O2. In this study, Shellac but not Carnauba wax applied onto late-picked fruit (3.6 starch index, 3% BBD and 29% watercore at harvest) 19 days after harvest increased BBD after 1 month of air storage at 0°C, although the disorder did not
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O.L. Lau / Posthar6est Biology and Technology 14 (1998) 131–141
Fig. 2. Influence of storage CO2, O2 and harvest maturity (starch index) on the incidence of Braeburn browning disorder (BBD) and internal cavities (IC) in ‘Braeburn’ apples after 4.5 months of storage at 0°C and a 7-day shelf-life test in air at 20°C (n = 5 orchards; 1996).
increase further during shelf-life tests or additional time in air storage (Table 4). However, development of IC was unaffected by either wax treatments (data not shown). Hagenmaier and Shaw (1992) have shown that permeability to CO2 and O2 is lower for coatings made from Shellac and rosin than those made from Carnauba and other waxes. Among ten commercial apple cultivars tested, ‘Braeburn’ had the highest fruit density (Table 5). Gas diffusion rates across the cortical tissues of ‘Braeburn’ would, therefore, be lower than those of other cultivars. Rajapakse et al. (1990) have reported that skin resistance of ‘Braeburn’ to O2 diffusion is two and four times higher than those of ‘Granny Smith’ and ‘Cox’s Orange Pippin’,
respectively. Internal O2 under the skin and in the central cavity, intercellular space volume and O2 diffusivity in the flesh are lower for ‘Braeburn’ than for ‘Granny Smith’ and ‘Cox’s Orange Pippin’, and high resistance contributes to susceptibility of ‘Braeburn’ to BBD and IC. Park et al. (1993) has observed that skin discoloration associated with low O2 is positively correlated with fruit resistance to gas diffusion at harvest. Similarly, Johnson et al. (1998) have found association of increased internal CO2 injury with high resistance to gas diffusion. When high resistance apple cultivars such as ‘Braeburn’ are placed in low O2 or elevated CO2 regimes, the internal atmospheres may be modified to a point at which BBD and IC are readily induced.
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139
Table 4 Effect of postharvest wax treatment on incidence of Braeburn browning disorder (BBD) in late-picked ‘Braeburn’ apples after 1, 2 and 3 months of air storage at 0°C (n= 5 orchards; 1996) Wax treatment
BBD incidence (%) 9Wax, then 0°C air storage for:
Control Carnauba Shellac
Plus 7 days in air at 20°C for:
1 month
2 months
3 months
1 month
2 months
3 months
11 a 15 a 25 b
14 a 24 b 23 ab
11 a 14 ab 28 b
13 a 23 b 37 c
13 a 15 a 30 b
13 a 9a 27 b
Characteristics of fruit at harvest: 3.6 starch index, 97 N firmness, 3% BBD, 29% watercore. After 19 days in 0°C air before waxing: 14% BBD and 15% watercore. Mean separation, within column, by Duncan’s new multiple range test at P50.05.
3.2.6. Storage temperature Storage temperature between 0 and 4.0°C had no significant effect on BBD and IC in ‘Braeburn’ apples held in CA at 0, 1.7 and 3.0°C or in air at 0, 2 and 4°C (data not shown), indicating that BBD and IC are not low-temperature disorders. Similar observations have been made with New Zealand-grown ‘Braeburn’ (Elgar et al., private communication). The use of elevated storage temperatures, however, decreased flesh firmness in CA-stored fruit in two of three seasons (1994 and 1996) and increased core browning in air-stored fruit in 1996 (Table 6). Table 5 Density of ten British Columbia-grown apple cultivars (size 88 apple; 7.8–8.0 cm in diameter; 1996) Apple cultivar ‘Braeburn’ ‘Fuji’ ‘Gala’ ‘Red Delicious’ ‘Jonagold’ ‘Empire’ ‘Elstar’ ‘Spartan’ ‘McIntosh’ ‘Golden Delicious’
Fruit density (kg m−3) 882 g 862 f 841 e 827 d 816 c 815 c 800 b 790 a 788 a 788 a
Means of nine 20-fruit samples (3 packed boxes×3 replicates each) from a packing house in Oliver, BC. Mean separation, within column, by Duncan’s new multiple range test at P5 0.05.
4. Concluding remarks Storage of ‘Braeburn’ apples in 1.2–1.5% O2 + 1.0–1.2% CO2 atmospheres established within 2 to 3 days of harvest improved the retention of flesh firmness and titratable acidity and reduced the incidence of scald and core browning compared to air storage. However, the CA atmospheres markedly increased the incidence of BBD and IC after cool growing seasons especially in fruit picked at a more advanced maturity. Occurrence of these disorders were increased also by Shellac waxing that increases skin resistance to gas diffusion and by storage in elevated CO2 and/or low O2 atmospheres. An ultra-low CO2 (close to 0.1%) and \ 1.5% O2 atmosphere might be acceptable for storage of ‘Braeburn’ apples for 4–6 months after warm growing seasons ( \ 1300 DD10 between 1 May and harvest). A slow or 14-day delay in establishing the CA conditions (Elgar et al., 1998) may be required to reduce the risks of BBD and IC. After a cool growing season, however, the fruit were best held in ventilated air storage for not more than 4 months to reduce the risks of CO2- and low O2-induced BBD and IC. It would be interesting to determine the biochemical basis of BBD and IC development and whether these disorders can be predicted based on preharvest orchard temperature and internal CO2 and O2. The benefit of pre-CA delays in 0°C air also needs to be ascertained for the control of BBD in BC-grown ‘Braeburn’ apples.
O.L. Lau / Posthar6est Biology and Technology 14 (1998) 131–141
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Table 6 Effect of storage temperature on flesh firmness and core browning (CB) in ‘Braeburn’ apples held in CA or air Year
Storage
Duration (months)
Temperature (°C)
Firmness (N)
CB incidence (%)
1994
CA
6
0 1.7 3.0 Significance
76 70 67 **
1 0 2 NS
1995
CA
6
0 1.7 Significance
81 78 NS
9 5 NS
1996
CA
6
0 1.7 Significance
83 81 **
13 15 NS
Air
4
0 2.0 4.0 Significance
76 63 60 ***
8 13 34 ***
1994–1995, 1.5% O2+1.2% CO2; 1996, 1.5% O2+0.1 to 3.0% CO2. Characteristics of fruit at harvest: 218 g per fruit, 3.6 starch index, 97 N firmness, 3% BBD, 29% watercore. Significance: NS, non-significant; significant at * P50.05, ** P50.01, *** P50.001.
Acknowledgements This work was not possible without the technical assistance of R. Yastremski, P. Schofield, W. Urban and S. Horton, and the financial support of the Okanagan Valley Tree Fruit Authority.
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