Flesh Browning Disorder of 'Pink Lady' Apples
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Th e Flesh Browning Disorder of ‘Pink Lady’™ Apples Hannah James1 and Jenny Jobling2 1Department of Horticulture, Cornell University, Ithaca, NY 2Applied Horticultural Research, Sydney, NSW, Australia he ‘Cripps Pink’ apple has become a popular vari- to be below the ety both in Australia where it was developed and acceptable lim- Tinternationally due to the distinctive fl avor charac- its for fi rmness teristics and at- and had also de- tractive appear- veloped an un- “Our research in Australia has shown that ance of the fruit. acceptable level Figure 1. Radial fl esh browning disorder (RFB) of the fl esh browning disorder of ‘Pink To establish a of skin greasi- ‘Pink Lady’™ apples in Australia. Lady’™ apples is three distinct disorders strong position ness prompting (radial fl esh browning, diff use fl esh among new and stricter quality guidelines to be enforced. In addition, a fl esh browning and CO2 injury.) Radial fl esh popular culti- browning disorder was detected; in 2003, 35 containers of browning was found to occur in warm vars, the ‘Cripps ‘Pink Lady’TM apples that had been exported from Australia growing districts and is characterized by Pink’ apple has to the United Kingdom were rejected due to the presence of browning of the vascular tissue of the been extensively the fl esh browning disorder, representing a large economic fruit, with the cortex tissue remaining marketed under loss to Australian apple growers and the potential loss of TM clear and relatively unaff ected. the trademarked the reputation of the ‘Pink Lady’ brand. TM Diff use fl esh browning was found to name ‘Pink La- Th e fl esh browning disorder of ‘Pink Lady’ apples TM occur in cool growing districts and is dy ’. Th e ‘Pink was found to be sporadic in nature with symptoms not Lady’TM trade- being present in every season or growing district. Th is characterized by browning throughout mark is owned unpredictability rapidly undermined the established trade the cortex tissue of the fruit, with the by Apple and confi dence in the cultivar and began to erode the market vascular tissue remaining clear and Pear Ltd Aus- advantage that had been developed. Anecdotal reports relatively unaff ected. CO injury is 2 tralia and a roy- suggested that a range of factors might be responsible for characterized by the appearance of lens alty of $1 US per the development of the disorder. Th ese factors included shaped pits and cavities throughout carton of apples fruit maturity at harvest, fruit nutrition, storage conditions the cortex of the fruit and occurs covers licensing such as the storage temperature and atmosphere as well as when the fruit are stored in controlled and marketing orchard climatic conditions. atmosphere storage with the level of costs associated In order to determine the pre- and postharvest fac- CO2 above 1%.” with trademark tors that were responsible for the development of the fl esh branding and browning disorder during storage, a research project fa- development. cilitated by Horticulture Australia Ltd in partnership with Th e success of this international marketing resulted in the Apple and Pear Australia Ltd was established. Th e project ‘Pink Lady’TM apple cultivar becoming popular in interna- was collaborative between researchers in Australia, New tional markets, especially throughout Europe where a price Zealand, Italy and the United States. premium of up to four times that of other apple cultivars was received (Studdert, 2002). Classifi cation of the Flesh Browning Disorder To use the ‘Pink Lady’TM trademark, ‘Cripps Pink’ apples Th e fl esh browning disorder of ‘Pink Lady’TM apples must meet strict quality guidelines including a minimum was originally thought of as a single disorder. However, this area of pink blush on the skin, fl esh fi rmness, total soluble research project has demonstrated that it can be classifi ed solids, titratable acidity and absence of disorders. However, into three distinct disorders (radial fl esh browning, dif- TM in 2000, the quality of exported ‘Pink Lady’ apples was fuse fl esh browning and CO2 injury) based on contrasting found to have declined. Th is was likely due to the fruit be- physiology as well as the visual appearance of the browning ing harvested late (Wilkinson, 2000) as growers attempted within the fruit. to meet the strict blush guidelines. Shipments arriving in 1. Radial fl esh browning disorder: Radial fl esh brown- the United Kingdom from Australia following fi ve weeks ing (RFB) is a senescent disorder, aggravated by late harvest, of air storage and a six week sea freight voyage were found low temperature storage and high CO2 in the storage atmo- NEW YORK FRUIT QUARTERLY . VOLUME 16 . NUMBER 2 . SUMMER 2008 23 sphere. Radial fl esh browning was found to occur in warm growing districts and is char- acterized by browning of the vascular tissue of the fruit, with the cortex tissue remaining clear and relatively unaff ected (Figure 1). It is thought that the small size of the vascular cells restricts the movement of CO2 throughout the fruit leading to the buildup of toxic quantities of CO2 in these areas resulting in cell death and the charac- teristic pattern of browning. Figure 2. Diff use fl esh browning disorder (DFB) of Figure 3. CO2 injury to the fl esh of of ‘Pink Lady’™ Radial flesh browning has a ‘Pink Lady’™ apples in Australia. apples in Australia. high area of browning at the stem end of the fruit, decreasing in area at the calyx end of conditions that promote and exacerbate the development the fruit. In fruit with mild RFB, symptoms may sometimes of the diff erent disorders. No incidence of RFB, DFB or CO2 be observed only at the stem end of the fruit. injury has been observed in ‘Pink Lady’TM apples at harvest, 2. Diff use fl esh browning disorder: Diff use fl esh indicating that these are storage disorders. browning (DFB) is a chilling injury, occurring when sus- Over three consecutive seasons beginning in 2004, a ceptible ‘Pink Lady’TM apples are stored below 38oF. Diff use number of storage conditions were examined in order to fl esh browning was found to occur in cool growing districts determine their infl uence on the development on RFB and and is characterized by browning throughout the cortex DFB of ‘Pink Lady’TM apples during storage. tissue of the fruit, with the vascular tissue remaining clear In the 2004 season, optimal (starch index = 3.5) and and relatively unaff ected (Figure 2), thus in direct contrast late (starch index = 8.5, on a scale of 1 to 10) harvested with RFB. Th e cortex cells of the fruit are much larger than ‘Pink Lady’™ apples were stored at 32oF in either air or air + the vascular cells and also have much thinner cell walls. It 1% CO2 for up to seven months. Following four months of is thought that these larger cells are more prone to collapse storage, the incidence of RFB was higher in fruit stored with due to membrane damage resulting from chilling injury 1% CO2 than in air stored fruit (Figure 4). In this season, than the smaller and thicker walled vascular cells. Diff use the incidence of DFB was extremely high (between 92 and fl esh browning has a high area of aff ected tissue at the stem 100% of fruit were aff ected). However, as shown in Figure and calyx ends of the fruit, with a lower area of browning 4, the incidence of DFB was lower in fruit that were stored in the middle section of the fruit. with 1% CO2 than in fruit that were stored in air. Th is dif- TM ference between the response of RFB and DFB to added 3. CO2 injury: CO2 injury of ‘Pink Lady’ apples was CO in the storage atmosphere indicates the contrasting expressed in a similar fashion to CO2 injury that has been 2 observed in other apple cultivars. Th e disorder is charac- physiology between the two disorders. For both RFB and terized by the appearance of lens shaped pits and cavities DFB, fruit that were harvested late had a higher incidence of browning than fruit that were harvested at the optimal throughout the cortex of the fruit. CO2 injury of ‘Pink Lady’TM apples was only found to occur when the fruit were maturity for long-term storage. A similar pattern of brown- stored in controlled atmosphere storage with the level of ing was observed following seven months of storage. In the 2005 season, optimal (starch index = 3.5) and late CO2 above 1%. (starch index = 8.5) harvested ‘Pink Lady’TM apples were Factors infl uencing the development of the flesh stored in air at either 32oF or 38oF for seven months. Th e browning disorder incidence of RFB was reduced by half by storing the fruit at Th e fl esh browning disorders of ‘Pink Lady’TM apples 38oF (Figure 5). Th e incidence of DFB however was reduced are the result of a complex combination of factors. In this from as high as 74% down to 4% by storing the fruit at 38oF. research, those factors can broadly be categorized as pre- Th is shows that the DFB disorder of ‘Pink Lady’TM apples is harvest (orchard) and postharvest (storage) conditions. a chilling injury that can be reduced to within commercial threshold levels by storing the fruit at 38oF. However, the 1. Postharvest conditions incidence of RFB was not reduced to commercial levels, Th e susceptibility of ‘Pink Lady’TM apples to developing suggesting that further factors are involved in the develop- RFB, DFB or CO2 injury during storage can be infl uenced ment of this disorder.