History, Current Situation and Future Prospects for Dynamic Controlled Atmosphere (DCA) Storage of Fruits and Vegetables, using Chlorophyll Fluorescence (October, 2014)

Robert K. Prange¹, A. Harrison Wright², John M. DeLong³ and Angelo Zanella⁴

¹ Faculty of Agriculture, Dalhousie University, Truro, NS, Canada

² Laval University, Quebec City, QC, Canada

³Agriculture and Agri-Food Canada, Atlantic Food and Horticulture Research Centre, Kentville, NS, Canada

⁴ Laimburg Research Centre for Agriculture and Forestry, Laimburg 6 – Pfatten (Vadena), 39040 Auer (Ora), Italy

Keywords: diphenylamine, superficial scald, lower oxygen limit, stress detection, flavour life

Abstract

The use of chlorophyll fluorescence in fruit and vegetable storage (HarvestWatch™) was first introduced at the ISHS CA symposium in 2001 in Rotterdam, the Netherlands and was first commercially adopted in the 2003-2004 storage season in Washington State, USA and South Tyrol, Italy. Although there are many potential post-harvest applications for chlorophyll fluorescence that will be reviewed, research and commercial adoption has focussed primarily on its use in optimising the O₂ concentration in dynamic controlled-atmosphere (DCA) storage of fruits and vegetables. This is achieved through a novel method of detection of a sudden change in fluorescence at the lower O₂ limit (LOL), which we refer to as Dynamic Controlled-Atmosphere-Chlorophyll Fluorescence (DCA-CF). The reasons for its adoption are: real-time monitoring and control of product, pesticide-free technique, accurate determination of LOL, control of storage disorders,_­­ especially superficial scald in susceptible apple and pear cultivars without use of pesticides such as diphenylamine (DPA), improved retention of quality, possible flavour enhancement and detection of senescence, decay or incorrect storage conditions, i.e. temperature. A summary of the current use of HarvestWatch™ will be presented. Preliminary results from applications in other high value fruits, e.g. extension of green-life in banana, ‘programmed DCA-CF’ for avocado, will be presented as evidence of possible future applications.

 

INTRODUCTION

The development of controlled atmosphere (CA) technology can be broken into three eras. In the first era, CA storage involved a search for ways to maintain a constant temperature and atmosphere with the introduction of mechanical refrigeration, air-tight rooms and use of the product’s respiration to lower O₂ and increase CO₂. In the second era, technology appeared that provided more accurate gas measurement that allowed for the control of gas levels at constant concentrations to a fraction of a percent. This led to a more rapid establishment of CA conditions. However, the goal in these first two eras to quickly establish specific and constant gas levels, i.e., use CA technology to control physiology, did not always lead to better post-storage results. As a consequence, a new approach, or 3^rd era, was needed in which the product physiology controlled the CA technology. In other words, CA conditions are adjusted dynamically to optimise the product’s response to CA.

This 3^rd era, which we will call the Dynamic Controlled Atmosphere (DCA) era, actually involves 2 phases. In the first phase, the dynamic nature of the CA conditions was solely determined from empirical data. In the second and current phase, bio-sensing of the product physiology is employed to reset the CA conditions to reflect the changing metabolic condition of the stored product. This presentation will discuss these two phases in more detail.

 

HISTORY OF DYNAMIC CONTROLLED ATMOSPHERE (DCA)

 

Phase 1: DCA using empirical data

Alique and De la Plaza (1982) are believed to be the first to use the term ‘dynamic controlled atmosphere’. Taking advantage of research showing that apples varied over storage time in their susceptibility to CO₂ damage, they proposed to increase CO₂ after 1 month from 0 to 2%, and after 2 months to 5%, at constant 3% O₂. Qi et al. (1989) introduced the term ‘two-dimensional dynamic controlled atmosphere storage’ or ‘TDCA’ in which the first dimension is a change in storage temperature from 10-15ºC to 0ºC and the second dimension is a change in storage CO₂ from an initial 10-15% to ca. 6% with a constant 3% O₂. Mattheis et al. (1998) used the term ‘dynamic atmosphere storage’ in which temperature and CO₂ are kept constant and O₂ is varied from 1% to ambient air for periods of 1, 2 or 3 days and returned to 1% O₂.

Phase 2: DCA using product physiology

Dynamic controlled atmosphere storage using product physiology, rather than static general recommendations, was described conceptually by Wollin et al. (1985) at the 4^th National Controlled Atmosphere Research Conference. They speculated that the respiratory quotient (RQ) may be the method to determine the lowest oxygen level but identified several constraints to its use outside carefully-controlled lab conditions. The concept of Wollin et al. (1985) was used to devise an automated test system that sought out the optimum combination of temperature, O₂ and CO₂ to achieve minimum respiration (Wolfe et al., 1993), but no data or evidence of its success are provided. By 2003, it was well-recognised that the dynamic response of the stored commodity could be incorporated into mathematical models to determine the adjustments that need to be made to optimize the storage atmosphere (Saltveit, 2003).

One of the simplest ways to use product physiology to control the O₂ content in CA is measurement of ethanol content in the store room, based on the assumption that the appearance of ethanol signals the onset of fermentation in the stored crop. Measuring atmospheric ethanol is further supported by the observation that there is a stable ratio between the ethanol content in the tissue and the atmosphere around the crop (North and Cockburn, 1975). However, they warned that this stable ratio is suitable for stores equipped with lime CO₂ scrubbers but not for stores equipped with activated charcoal scrubbers. The first report of successful application of O₂ control using ethanol was by Schouten (1995) who concluded that a ‘Dynamic Control System’ (DCS) for the oxygen content on CA rooms is possible, based on his results with ‘Jonagold’ apple and Brussels sprouts. Schouten et al. (1997) confirmed that DCS storage of ‘Elstar’ apple, in which O₂ is adjusted to maintain ethanol below 1 ppm in the headspace (0.3-0.7% O₂ + <0.5% CO₂) maintains fruit quality better than ULO-stored fruit (1.2% O₂ + 2.5% CO₂).

A closely-related approach, ILOS+, has been introduced in recent years. Initial Low Oxygen Stress (ILOS) is a technique first described by Eaves et al. (1969a,b) that uses short (up to 2 weeks) low O₂ stress treatments, i.e. typically but not always ≤0.5%. ILOS+ is repeated applications of low oxygen stress at various times in the storage period with the addition of destructive ethanol tissue analysis used to determine when to stop treatment.

The above methods rely on measuring changes in ethanol in the store room or in tissue that could signal the product is at or near its lower O₂ limit (LOL). The most recent system to determine the LOL is the use of chlorophyll fluorescence (DCA-CF) which does not need to measure ethanol or other fermentative products. The discovery of a sudden and reversible ‘spike’ in CF when O₂ is lowered below the product’s apparent LOL and a commercial system using this discovery (HarvestWatch™) was first presented at the ISHS CA symposium in Rotterdam, the Netherlands in 2001, and subsequently published (Prange et al., 2002, 2003). They concluded it may be a very sensitive, non-destructive method of dynamically controlling the O₂, and possibly the CO₂ environment, according to the unique requirements of each product. Prange et al. (2003) describes the commercial version of this technology, which measures chlorophyll fluorescence on a group of fruit or vegetables using a periodic low irradiance. It was first adopted commercially in the 2003-2004 storage season in Washington State, USA and South Tyrol, Italy. This system is a pulse frequency modulated (PFM) proprietary technology which uses extrapolation to produce a theoretical estimate of the minimum fluorescence (F_o) parameter for which they coined a new term, F_α. With DCA-CF, one can detect changes in the LOL and immediately alter the O₂ level in the store room. The LOL varies with the product, e.g. cultivar, and time in storage (Table 1).

Table 1. Detection of the lower oxygen limit (LOL) by DCA-CF, as affected by apple cultivar and storage time.
	LOL (% O2)
Apple cultivar	10-19 October	1-4 December
Delicious	0.85	0.47
Golden Delicious	0.92	0.45
Honeycrisp	0.90	0.50
Empire	0.90	0.88

In this example, three of the four apple cultivars had a drop in the LOL of ca. 0.4% O₂ and in the 4^th cultivar, ‘Empire’, there was no change in LOL. Subsequent research shows that this chlorophyll fluorescence system is sensitive to not only the LOL but other stresses experienced by stored product, e.g. CO₂, low temperature (chilling), 1-MCP application, and the presence of toxic ammonia refrigeration gas and water loss (Prange et al., 2010; Prange et al., 2012). All of these stresses, except for water loss, result in an immediate increase in F_α, similar to the increase caused by O₂ below the LOL.

CURRENT SITUATION

When it was first introduced, the application of the chlorophyll fluorescence method in DCA was described as dynamic low-O₂ controlled atmosphere (DLOCA) (DeLong et al., 2004). Another term used by a few researchers was fluorescence CA (FCA) (Vanoli et al., 2007). Neither of these terms has been embraced by other users.

Although DCA did not initially refer solely to the DCA-chlorophyll fluorescence (CF) method, many researchers and users now refer to the two DCA-ethanol methodologies above as DCS and ILOS+, respectively, and shortened DCA-CF to just DCA, e.g., Zanella et al. (2005, 2008); Raffo et al. (2009); Gasser et al. (2010); Streif et al. (2010). The discussion below DCA-CF will be used to distinguish this method from the other DCA-type methods.

DCA-CF is the most widely-known and used method for optimising CA conditions. It is marketed by Isolcell Italia S.p.A. and it is used around the world in commercial apple (Prange et al., 2010) and pear storages (Prange et al., 2011). The current estimate of its usage is >330,000 tonnes in >1300 DCA-CF rooms in >15 countries. DCS is marketed by Storex BV and is used in ca. 170 store rooms of ‘Elstar’ and ‘Jonagold’ apples in the Netherlands and there are ca. 10 DCS systems in other countries. ILOS+ is used on ca. 2400 tonnes of stored apples (cultivars not specified) in the South Tyrol (Alto Adige) region of Italy.

Most of the published DCA-CF research has been conducted on apples and pears (Table 2) but there are research and commercial trial reports on a variety of other fruits and vegetables.

Table 2. List of publications providing information on DCA-CF use in fruits and vegetables.
Commodity	Cultivar	Publications
Fruits
Apple	Braeburn	Gasser et al., 2008; Lafer, 2008; Lafer, 2009;   Poldervaart, 2010a; Prange et al., 2012; Withnall, 2008
	Cortland	DeLong et al., 2004, 2007; Prange et al., 2012; Wright et   al., 2012
	Cripp’s Pink (Pink Lady)	Withnall, 2008; Prange et al., 2012
	Delicious (Red)	DeLong et al., 2004, 2007; Lafer, 2009; Prange et al.,   2012; Stephens and Tanner, 2005; Withnall, 2008; Wright et al., 2012
	Elstar	Gasser et al., 2008; Köpcke, 2009; Poldervaart, 2010a;   Prange et al., 2012
	Fuji	Withnall, 2008; Zanella et al., 2008
	Gala	Withnall, 2008; Zanella et al., 2008
	Golden   Delicious	DeLong et al., 2004; Gasser et al., 2008; Poldervaart,   2010a; Prange et al., 2012; Withnall, 2008; Zanella et al., 2008
	Honeycrisp	DeLong et al., 2004; Prange et al., 2010; 2012; Wright et   al., 2008, 2010, 2011, 2012
	Granny Smith	Lafer, 2009; Prange et al., 2012; Wright et al., 2012;   Withnall, 2008; Zanella et al., 2005
	Idared	Poldervaart, 2010a; Prange et al., 2012
	Jonagold	DeLong et al., 2004; Prange et al., 2012
	Maigold	Gasser et al., 2008; Poldervaart, 2010a
	McIntosh	DeLong et al., 2004; Prange et al., 2002; 2003
	Northern Spy	Prange et al., 2005
	Pinova (Piñata)	Raffo et al., 2009
	Topaz	Lafer, 2009; Poldervaart, 2010a,b
Avocado	–	Prange et al., 2003; Yearsley et al., 2003
	Hass	Burdon, 2009; Burdon and Lallu, 2008; Burdon et al.,   2008; 2010; Prange et al., 2002; Yearsley et al., 2003
Banana	–	Prange   et al., 2002; 2003
Kiwifruit	–	Prange   et al., 2002; 2003
	Hayward	Lallu   and Burdon, 2007
Mango	–	Prange   et al., 2002; 2003
Pear	–	Prange   et al., 2003
	Abbé Fétel (Abaté   Fétel)	Rizzolo   et al., 2008; Vanoli et al., 2007, 2010a,b; Zerbini and Grassi, 2010
	Bartlett   (Williams Bon Chrétien)	Mattheis,   2007; Prange et al., 2002, 2011; 2012
	Conference	Zerbini   and Grassi, 2010
	d’Anjou	Mattheis,   2007; Mattheis and Ruddell, 2011; Prange et al., 2011; 2012
	Forelle	Prange et al., 2011
	Packham’s   Triumph	Prange et al., 2011, 2012
	Spadona	Prange et al., 2011
	Uta	Lafer, 2011
Vegetables
Asparagus	–	Prange et al., 2005
Broccoli	–	Prange et al., 2005
Cabbage	–	Prange et al., 2003
Pepper (Green)	–	Prange et al., 2003
Lettuce	Iceberg	Prange et al., 2003, 2005
	Romaine	Prange et al., 2003
Spinach	–	Prange et al., 2012; Wright et al., 2011, 2012

 

Costs and Benefits

The primary goal of using CA-type technology is to lower the oxygen to the lowest acceptable level to achieve maximal quality benefits. The introduction of DCA-CF and the two ethanol-based technologies has shown the industry that their CA systems can be held at much lower O₂ levels, e.g. <0.5%, than previously believed and that this produces a measurable quality and financial benefit. More specifically, these new technologies are enhancements to the existing CA systems so there is no need to change to a new storage infrastructure. The enhancements to existing CA facilities are one or more of the following one-time investments: improving air-tightness, O₂ removal capacity and CO₂ scrubbing capacity. The CO₂ scrubbing capacity is important because, in the case of apple and pear, lowering the O₂ concentration should be matched with a lower CO₂ concentration to avoid CO₂-induced disorders. Fortunately, most modern CA facilities require negligible investment to meet this requirement. In the case of DCA-CF, there is a one-time capital expenditure for chlorophyll fluorescence sensors and software. Since DCA-CF costs are one-time capital expenditures, there are no recurring annual charges associated with other chemical-based alternatives and it adds to the asset value of the storage facility.

The technical features of DCA-CF that are appealing to users are:

•           Non-destructive measurements on large surface areas can be taken of any chlorophyll-containing fruit or vegetable.

•           The measurement is rapid and frequent.

•           The method is non-chemical.

•           Real-time monitoring of produce allows for on-site or remote monitoring and archiving of data for future reference.

•           There is no calibration needed while in operation

•           It detects changes in the product due to senescence, decay or incorrect storage conditions, i.e. temperature, unwanted toxic gases such as ammonia refrigerant

Its non-chemical feature makes it appealing to industrial users who wish to reduce post-harvest chemical use or store ‘organic’ product. Others have adopted it because it is a one-time capital expense that can have a pay-back period of 2-3 years, compared with repeated annual expense with competing chemical-based methods.

The benefits are largely the benefits already known to be associated with use of CA, but more enhanced. In addition to the enhancement of desirable quality attributes such as storage time extension, reduced bruising, higher packout percentage, and firmness and taste retention, some specific benefits have also been realised.

The most noteworthy benefit is the control of several storage disorders, especially superficial scald in apples and pears. Although Smock (1979) did not identify superficial scald control as a benefit of standard CA, there is substantial scientific literature showing that superficial scald is controlled by very low O₂ (see review by Prange et al., 2011). Until recently, the predominant scald control method was the use of diphenylamine (DPA) or ethoxyquin (pears only). With the advent of DCA-CF the apple and pear industry has realised that chemicals are not needed to control scald. Another factor is that DPA and ethoxyquin are no longer acceptable in the EU countries of Europe, based on an EU final decision in June, 2012 (R. Hurndall, pers. communication).

As a result, the apple industry in South Tyrol (Alto Adige), Italy decided to stop using DPA and the current 2011-2012 is the 2^nd storage season without any DPA applied to the apples. In the most recently-completed season, ca. 59.5% were held in CA or ULO without any scald control treatment (Zanella et al., 2012). The remaining 40.5% were treated for scald control primarily with 1-MCP or DCA. Some late-stored (ca. 10 months) fruit were treated with 1-MCP and then held in DCA-CF or ILOS to ensure scald control. In 2011-2012 in the South Tyrol, 47% of DCA-CF stores held the scald-susceptible cultivars, ‘Red Delicious’ and ‘Granny Smith’ with 12 cultivars comprising the remainder (Figure 1).

Fig. 1. Apple cultivars held in DCA-CF in the 2011-2012 storage season in the South Tyrol, Italy. Total amount stored in DCA is ca. 139,000 tonnes.

After its introduction, commercial users of DCA-CF have reported anecdotally that DCA-CF enhances flavour of cultivars such as ‘Pink Lady’ and ‘Granny Smith’, compared with other storage technologies being used. These reports were confirmed by Zanella et al. (2005) and Raffo et al. (2009) who concluded that DCA-CF storage technology, besides avoiding any chemical treatment, can preserve apple flavour/aroma compounds better than 1-MCP + ULO during long-term storage. Raffo et al. (2009) observed that DCA-CF favoured the production of branched-chain esters over straight-chain esters. This is an unforeseen benefit of DCA-CF that may extend beyond apple cultivars and suggests that DCA-CF may be able to alter flavours and aromas in a predictable way and/or increase flavour-life of the product.

FUTURE PROSPECTS

DPA replacement

The decision to stop the use of DPA in the EU will increase the demand for DPA alternatives, including DCA-CF, within Europe and in countries exporting apples and pears to Europe. There are already DCA protocols for apple cultivars and this will have to be done for pear cultivars, especially cultivars already being stored commercially in DCA-CF or in commercial trials, e.g. ‘Williams’, ‘Forelle’, ‘Conference’, ‘Abbé Fétel’ and ‘Rocha’.

Energy conservation

DCA-CF results in a substantial reduction in fruit respiration, with the result that higher storage temperatures are possible; thus saving energy (J. Streif, as quoted in Poldervaart, 2010). In New Zealand, experiments are being conducted using a combination of DCA-CF and high temperature storage to achieve energy savings during storage, and/or avoid chilling-related storage disorders in ‘Royal Gala’ and ‘Pink Lady’ apples (N. Lallu, pers. comm.). Preliminary results show that at 5°C storage savings of 35% were possible during cooling and 15% during storage. In addition, flesh browning in ‘Pink Lady’ could be avoided by storage at 3 °C in DCA-CF. In yellow-fleshed kiwifruit, chilling injury was avoided by storage at 7 °C in DCA-CF whilst maintaining the same firmness as fruit stored at 0 °C in air (N. Lallu, pers. comm.).

Long distance transport of high-value tropical fruits

Laboratory research results on banana show that the ‘green life’ of the bananas was increased in DCA-CF, compared with CA and air (Figure 2).

Fig. 2. Extension of ‘green life’ of bananas after 26 days in storage, using DCA-CF, compared with CA and refrigerated air (RA).

In addition, the DCA-CF appeared to reduce the amount of uneven ripening which is a major loss in the banana market. Research on avocado fruit has shown that DCA-CF can provide desirable benefits such as prolonged storage time, short ripening time and less decay (Figure 3, from Burdon, 2009).

Fig. 3. Sample of avocado in tray (left) and chlorophyll FIRM sensor in lid (right) before placing over avocados (from Burdon, 2009).

These research results were recently proven on a commercial scale (Washington, 2012) in December, 2011. Two thousand trays (ca. 11,000 kg) of avocados were shipped in ocean containers, using a ‘programmed DCA-CF’ whereby a low O₂ stress is automatically applied at set intervals, enabling the avocados to arrive 50 days later in France with successful results. Based on this success, additional commercial shipments have been undertaken but results are not publically available.

This successful demonstration of DCA-CF to control ripening in avocado and banana either before or during shipping provides shippers with a new tool to maximise quality retention, market availability and financial returns. Further adoption is not inconceivable.

Flavour enhancement

Flavour is believed to be the first quality attribute that is lost during storage, preceding other quality indicators such as firmness and appearance (Kader, 2008). Since flavour maintenance or enhancement may improve a product’s market share in a competitive market, the ability of DCA-CF to provide an extension of the product’s flavour life may be an important reason why it may be adopted by some users in the future.

Literature Cited                             

Alique, R. and De la Plaza, J.L. 1982. Dynamic controlled atmosphere for apple storage. Proc. Meeting IIR Commissions B2, C2 and D1. Sofia, Bulgaria. p. 342-349.

Burdon, J. 2009. Dynamic CA storage of avocados: Technology for managing exports? http://www.avocadosource.com/Journals/AUSNZ/AUSNZ_2009/BurdonJ2009.pdf (accessed 9 May 2012).

Burdon, J. and Lallu, N. 2008. Dynamic controlled atmosphere storage of avocados: Technology for managing exports? New Zealand Avocado Growers’ Association Annual Research Report 8:123-126.

Burdon, J., Lallu, N., Haynes, G., McDermott, K. and Billing, D. 2008. The effect of delays in establishment of a static or dynamic controlled atmosphere on the quality of ‘Hass’ avocado fruit. Postharvest Biol. Technol. 49:61-68.

Burdon, J., Lallu, N., Haynes, G., Pidakala, P., Billing, D. and McDermott, K. 2010. Dynamic controlled atmosphere storage of New Zealand-grown ‘Hass’ avocado fruit. Acta Hort. 876:47-54.

DeLong, J.M., Prange, R.K., Leyte, J.C. and Harrison, P.A. 2004. A new technology that determines low-oxygen thresholds in controlled-atmosphere-stored apples. HortTechnology 14:262-266.

DeLong, J.M., Prange, R.K. and Harrison, P.A. 2007. Chlorophyll fluorescence-based low-O₂ CA storage of organic ‘Cortland’ and ‘Delicious’ apples. Acta Hort. 737:31-37.

Eaves, C.A., Forsyth, F.R. and Lockhart, C.L. 1969a. Influence of post-harvest anaerobiosis on fruit. In: Proceedings of the XII International Congress of Refrigeration; 1967, Madrid. Vol. 3: 307-313 [report 4.31].

Eaves, C.A., Forsyth, F.R. and Lockhart, C.L. 1969b. Recent developments in storage research at Kentville, Nova Scotia. Can. Inst. Food Technol. 2: 46-51.

Gasser, F., Eppler, T., Naunheim, W., Gabioud, S. and Hoehn, E. 2008. Control of the critical oxygen level during dynamic CA storage of apples by monitoring respiration as well as chlorophyll fluorescence. Acta Hort. 796:69-76.

Gasser, F., Eppler, T., Naunheim, W., Gabioud, S. and Bozzi Nising, A. 2010. Dynamic CA storage of apples: Monitoring of the critical oxygen concentration and adjustment of optimum conditions during oxygen reduction. Acta Hort. 876:39-46.

Kader, A.A. 1985. An overview of the physiological and biochemical basis of CA effects on fresh horticultural crops. In: Blankenship, S. (Ed.) Controlled Atmospheres for Storage and Transport of Perishable Agricultural Commodities. Proc. 4th Natl. Controlled Atmosphere Res. Conf., Raleigh, North Carolina. Hort. Rept. No. 126, Dept. Hort. Sci., North Carolina State Univ., Raleigh, NC, USA. p. 1-9.

Kader, A.A. 2008. Flavor quality of fruits and vegetables. J. Sci. Food Agric. 88:1863-1868.

Köpcke, D. 2009. Einfluss der Sauerstoff-Konzentration im Lager auf den Schalenfleckenbefall bei ‘Elstar’. Mitteilungen des Obstbauversuchsringes des Alten Landes 64:303-309.

Lafer, G. 2008. Storability and fruit quality of ‘Braeburn’ apples as affected by harvest date, 1-MCP treatment and different storage conditions. Act Hort. 796:179-183.

Lafer, G. 2009. Practical experience with new storage technologies in Austria – Dynamic CA (DCA) storage and SmartFresh™. European Fruit Growers Magazine 1(1):24-27.

Lafer, G. 2011. Effect of different CA storage conditions on storability and fruit quality of organically grown ‘Uta’ pears. Acta Hort. 909:757-760.

Lallu, N. and Burdon, J. 2007. Experiences with recent postharvest technologies in Kiwifruit. Acta Hort. 753:733-740.

Mattheis, J. 2007. Harvest and postharvest practices for optimum quality. Final Project Report. Project Number PR-04-433, Washington Tree Fruit Research Commission Research Reports (http://jenny.tfrec.wsu.edu/wtfrc/dbsearch.php).

Mattheis, J.P. and Rudell, D. 2011. Responses of ‘d’Anjou’ pear (Pyrus communis L.) fruit to storage at low oxygen setpoints determined by monitoring fruit chlorophyll fluorescence. Postharvest Biol. Technol. 60:125-129.

Poldervaart, G. 2010a. KOB storage day 2010: DCA storage goes from strength to strength. European Fruit Magazine 2(8):6-9.

Poldervaart, G. 2010b. DCA viable alternative for organic Topaz. European Fruit Magazine 2(8):15.

Prange, R.K., Delong, J.M., Leyte, J. C. and Harrison, P.A. 2002. Oxygen concentration affects chlorophyll fluorescence in chlorophyll-containing fruit. Postharvest Biol. Technol. 24:201-205.

Prange, R.K., Delong, J.M., Leyte, J. C., Harrison, P.A., Leyte, J.C. and McLean, S.D. 2003. Oxygen concentration affects chlorophyll fluorescence in chlorophyll-containing fruit and vegetables. J. Amer. Soc. Hort. Sci. 128:603-607.

Prange, R.K., Delong, J.M. and Harrison, P.A. 2005. Quality management through respiration control: Is there a relationship between lowest acceptable respiration, chlorophyll fluorescence and cytoplasmic acidosis? Acta Hort. 682:823-830.

Prange, R.K., DeLong, J.M. and Wright, A.H. 2010. Chlorophyll fluorescence: applications in postharvest horticulture. Chron. Hort. 50(1):13-16.

Prange, R.K., DeLong, J.M. and Wright, A.H. 2011. Storage of pears using dynamic controlled-atmosphere (DCA), a non-chemical method. Acta Hort. 909:707-717.

Prange, R.K., DeLong, J.M. and Wright, A.H. 2012. Improving our understanding of storage stress using chlorophyll fluorescence. Acta Hort. 945:89-96.

Qi, S., Wang, C.S., Li, Z., Liu, Y., Hua, X., Fang, J., Song, Z., Tian, Y., Li, X., Li, Z., Lu, M. and Wang, S. 1989. Effects of two-dimensiol dynamic controlled atmosphere storage on apple fruits. In: Fellman, J. (Ed.) Proc. 5th Intl. Controlled Atmosphere Res. Conf., Wenatchee, Washington, USA. Vol. 1, p. 295-305.

Raffo, A., Kelderer, M., Paoletti, F. and Zanella, A. 2009. Impact of innovative controlled atmosphere storage technologies and postharvest treatments on volatile compound production in cv. Pinova apples. J. Agric. Food Chem. 57:915–923.

Rizzolo, A., Vanoli, M., Grassi, M. and Eccher Zerbini, P. 2008. Gas exchange in 1-methylcyclopropene treated ‘Abbè Fètel’ pears during storage in different atmospheres. Acta Hort. 796:143-146.

Saltveit, M.E. 2003. Is it possible to find an optimal controlled atmosphere? Postharvest Biol. Technol. 27:3-13.

Schouten, S.P. 1995. Dynamic control of the oxygen content during CA storage of fruits and vegetables. In: De Baerdemaeker, J. and Vandewalle, J. (Eds.) Control Applications in Post-Harvest and Processing Technology CAPPT ‘95, 1^st IFAC/CIGR/EURAGENG/ISHS Workshop, Ostend, Belgium. p. 163-168.

Schouten, S.P., Prange, R.K., Verschoor, J., Lammers, T.R. and Oosterhaven, J. 1997. Improvement of quality of Elstar apples by dynamic control of ULO conditions. In: Mitcham, E.J. (Ed.) CA’97. Proc. 7^th Intl. Controlled Atmosphere Research Conf., Univ. Calif., Davis, California, USA. Vol. 2, p. 71-78.

Streif, J., Kittemann, D., Neuwald, D.A., McCormick, R. and Xuan, H. 2010. Pre- and post-harvest management of fruit quality, ripening and senescence. Acta Hort. 877:55-68.

Smock, R.M. 1979. Controlled atmosphere storage of fruits. Hort. Rev. 1:301-336.

Stephens, B.E. and Tanner, D.J. 2005. The Harvest Watch system – Measuring fruit’s healthy glow. Acta Hort. 687:363-364.

Vanoli, M., Rizzolo, A., Grassi, M. and Eccher Zerbini, P. 2007. Storage disorders and quality in ‘Abbé Fétel’ pears treated with 1-methylcyclopropene. In: Novel approaches for the control of postharvest diseases and disorders. Proc. Intl. Congress, Bologna, Italy, 3-5 May, 2007. p. 269-277.

Vanoli, M., Eccher Zerbini, P., Grassi, M. and Rizzolo, A. 2010a. Ethylene production and quality in 1-methylcyclopropene treated ‘Abbé Fétel’ pears after storage in dynamically controlled atmosphere. Acta Hort. 876:31-38.

Vanoli, M., Grassi, M., Eccher Zerbini, P. and A. Rizzolo. 2010b. Fluorescence, conjugated trienes, α-Farnesene and storage disorders in ‘Abbé Fétel’ pears cooled with different speeds and treated with 1-MCP. Acta Hort. 858:191-198.

Washington, G. 2012. New technology brings new opportunities for NZ avocados. http://www.foodproductiondaily.com/Processing/New-technology-brings-new-opportunities-for-NZ-avocados (accessed 9 June 2012).

Withnall, M. 2008. Alternative ‘dynamically controlled atmosphere’ technique for control of long-term storage disorders. The Fruit Grower (U.K.) 20 May 2008, p. 19-20.

Wollin, A.S., Little, C.R. and Packer, J.S. 1985. Dynamic control of storage atmospheres. In: Blankenship, S. (Ed.) Controlled Atmospheres for Storage and Transport of Perishable Agricultural Commodities. Proc. 4^th Natl. Controlled Atmosphere Res. Conf., Raleigh, North Carolina. Hort. Rept. No. 126, Dept. Hort. Sci., North Carolina State Univ., Raleigh, NC, USA. p. 308-315.

Wolfe, G.C., Black, J.L. and Jordan, R.A. 1993. The dynamic control of storage atmospheres. In: Blanpied, G.D., Bartsch, J.A. and Hicks, J.R. (Eds.) CA ’93. Proc. 6^th Intl. Controlled Atmosphere Research Conference, Cornell Univ., Ithaca, New York, USA. p. 323-331.

Wright, A.H., DeLong, J.M., Franklin, J.L., Lada, R.R. and Prange, R.K. 2008. A new minimum fluorescence parameter, as generated using pulse frequency modulation, compared with pulse amplitude modulation: F_α versus F_o. Photosyn. Res. 97:205-214.

Wright, H., DeLong, J., Harrison, P.A., Gunawardena, A.H.L.A.N. and Prange, R. 2010. The effect of temperature and other factors on chlorophyll a fluorescence and the lower oxygen limit in apples (Malus domestica). Postharvest Biol. Technol. 55:21-28.

Wright, A.H., DeLong, J.M., Gunawardena, A.H.L.A.N. and Prange, R.K. 2011. The interrelationship between the lower oxygen limit, chlorophyll fluorescence and the xanthophyll cycle in plants. Photosynth. Res. 107:223-235.

Wright, A.H., DeLong, J.M., Gunawardena, A.H.L.A.N. and Prange, R.K. 2012. Dynamic controlled atmosphere (DCA): Does fluorescence reflect physiology in storage? Postharvest Biol. Technol. 64:89-30.

Yearsley, C.W., Lallu, N., Burmeister, D., Burdon, J. and D. Billing, D. 2003. Can dynamic controlled atmosphere storage be used for ‘Hass’ avocados? Proc. V World Avocado Congress (Actas V Congreso Mundial del Aguacate). pp. 665-670.

Zanella, A., Cazzanelli, P., Panarese, A., Coser, M., Cecchinel, M. and Rossi, O. 2005. Fruit fluorescence response to low oxygen stress: modern storage technologies compared to 1-MCP treatment of apple. Acta Hort. 682:1535-1542.

Zanella, A., Cazzanelli, P. and Rossi, O. 2008. Dynamic controlled atmosphere (DCA) storage by the means of chlorophyll fluorescence response for firmness retention in apple. Acta Hort. 796:77-82.

Zanella, A., Cazzanelli, P., Rossi, O. and Ebner, I. 2012. Replacing DPA post-harvest treatment by strategical application of novel storage technologies controls scald in 1/10th of EU’s apples producing area. Acta Hort. (this issue)

Zerbini, P.E. and Grassi, M. 2010. Chlorophyll fluorescence and gas exchanges in ‘Abbé Fétel’ and ‘Conference’ pears stored in atmosphere dynamically controlled with the aid of fluorescence sensors. Acta Hort. 857:469-474