• store room with apple




  • Spinach Fluorescence photo

     



  • HarvestWatch system with labels


  • FIRM Sample chamber kennel

  • Sample system layout


  • HarvestWatch FIRM sensors in a commercial DCA store room


  •  
    DCA controls superficial scald




  • Dynamic Controlled Atmosphere (DCA) storage of fruit with HarvestWatch technology provides the marketplace with high quality fruit without the use of chemicals
  • Chlorophyll, a pigment found in all higher plants, is a fluorophore. This image of spinach chlorophyll dissolved in solution shows how chlorophyll fluoresces red
  • The HarvestWatch™ system is a specialised fluorometer developed by Dr. Robert Prange and colleagues (AAFC and Satlantic Inc., Nova Scotia, Canada) and distributed by Isolcell Italia S.p.A. It uses fluorescence (Fα) to let storage operators know when their fruit are stressed
  • FIRM sample chamber (kennel)
  • A typical HarvestWatch system with multiple hubs and sensors
  • Six chlorophyll fluorescence (HarvestWatch) FIRM kennels in a commercial apple DCA store room
  • DCA using the HarvestWatch system controls superficial scald in apples and pears

Articoli

History

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 3rd 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 3rd 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 4th 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 (Fo) parameter for which they coined a new term, Fα. 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 4th 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 Fα, 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 Grasso, 2010

Bartlett   (Williams Bon Chrétien)

Mattheis,   2007; Prange et al., 2002, 2011; 2012

Conference

Zerbini   and Grasso, 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 2nd 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).

Apple cultivars in DCA 2011-2012 South Tyrol

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).

 Effect of DCA on banana

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).

DCA of avocado

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.

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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.

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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: Fα versus Fo. 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.

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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.

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This new technology was developed and patented in Canada in 2001 by a research team led by Dr. Robert Prange and Dr. John DeLong. Further research evaluation was conducted internationally, especially by Dr. Angelo Zanella of the Agricultural Research Institute Laimburg Italy which led to commercialisation in the U.S.A and Italy in 2003-2004.

The technology detects stress, e.g., low oxygen, by continuously monitoring changes in the chlorophyll fluorescence of the stored product. The major application of HarvestWatch technology is in dynamic controlled atmosphere-chlorophyll fluorescence (DCA-CF) storage of fruits and vegetables.

By the end of 2015, close to 1/2 million tonnes of apples and pears were being stored in >1680 DCA-CF rooms in >15 countries worldwide.

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