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Post-harvest application of SmartFresh Quality System

SmartFreshSM Quality System is commonly applied to apples in the UK and throughout the world to maintain harvest attributes. It is an important supplementary measure to good storage practice and is particularly effective in maintaining the quality of fruit in-store and during subsequent marketing and distribution.

Extensive research was carried out at East Malling Research (EMR) from 2000 onwards under the sponsorship of Rohm and Haas. Most of the research at EMR was done on Bramley, Cox and Gala. SmartFreshSM was approved for use on UK apples in September 2003. Since that time there has been considerable commercial experience with the product and there are now recommendations for its use with the following apple varieties in store: Bramley, Cameo, Cox, Egremont Russet, Empire, Gala, Golden Delicious, Jonagold, Rubens and Spartan.

The active ingredient of SmartFreshSM is 1-methylcyclopropene (1-MCP) a potent inhibitor of ethylene action in plants. As it is very similar in its chemical structure to ethylene, it binds preferentially with ethylene receptors in the cells of the fruit at the beginning of fruit storage. Consequently, for a period after  SmartFreshSM application, apples are insensitive to ethylene and consequently ripening events are retarded.

SmartFreshSM is formulated as a powder that releases 1-MCP when mixed with water in the storage room. The process takes about 24 hours and does not leave any detectible residue on the apples or in the environment.

The application protocol decided universally for apples, based on work done in the UK and elsewhere, is 625 parts per billion of 1-MCP (calculated for empty store volume) applied for 24 hours with minimal delay between harvest and application.

SmartFreshSM is part of a quality control system and growers need to use the application service provided by Landseer Ltd, the nominated representatives of Agrofresh.

Once the suitability of the rooms has been determined, commercial applicators are prepared with an amount of SmartFreshSM that is appropriate for the volume of the store to be treated. Water is added and circulated through the SmartFreshTM via an integral battery-driven pump. The applicator is then inserted into the sealed store where it remains for approximately 24 hours. After treatment the store is operated normally.

The latest recommendations for how long different apple varieties will store after being treated with SmartFreshSM are found in the Optimal Storage Conditions chapter of this guide.

Results of SmartFreshSM research done at EMR are summarised in reports of EMRA Members’ Days on Top Fruit Storage (Johnson and Pearson, 2002; 2003) and elsewhere (Johnson, 2008). The benefits of SmartFreshTM for the main UK cultivars as determined from research done at EMR and from commercial experience are summarised below.

 

Cox’s Orange Pippin (and clones) – benefits

  • SmartFreshSM application provides a significant (>2-fold) extension to the storage life of fruit held in refrigerated air storage.
  • A combination of a lower storage temperature (1.5oC) and SmartFreshSM application was particularly beneficial to the quality of air-stored fruit.
  • SmartFreshSM application consistently improved retention of firmness and reduced weight loss in store.
  • Occasionally SmartFreshSM application resulted in reduced yellowing, higher soluble solids and acidity levels and less bitter pit.
  • Greatest effects of SmartFreshSM application were achieved on fruit picked at the correct stage of maturity for medium to long-term storage.

 

Cox’s Orange Pippin (and clones) – constraints / limitations

 

Stem end russet browning

In some commercial consignments of Cox treated in the UK and also in New Zealand the russetted areas of the fruit have darkened in response to SmartFreshSM application.  This known as stem end russet browning.

  • The precise cause of the disorder is unknown although it has been hypothesised that 1-MCP causes a stress response in the skin cells which leak cell contents that are rapidly oxidised to brown coloured compounds (McCormick and Streif, 2008).
  • Development of browning symptoms is inhibited by low temperatures and low oxygen conditions so fluctuations in temperature or atmosphere after treatment should be avoided.
  • Commercial experience also suggests that early picked fruit are particularly at risk from stem end russet browning.
  • Tables of storage conditions for Cox contain information to remind growers of practices that minimise this disorder.
  • It is advised by the suppliers (Landseer Ltd.) that SmartFreshSM application should be restricted to fruit where starch coverage is 70% or less.
  • This is to minimise the effects of stem end russet browning and encourage fruit above 75% starch and a pressure greater than 8.6 kg to be stored for March marketing without the use of SmartFreshSM.

Core flush

Perhaps the most significant adverse effects of SmartFreshSM is the increased susceptibility of stored fruits to core flush and flesh breakdown which has important limitations on the storage life of Cox stored in CA conditions.

  • In air storage, core flush was evident in fruit treated with SmartFreshSMafter 90 days but not after 60 days.
  • It is difficult to set a precise termination date for air-stored Cox apples treated with SmartFreshSM.
  • It is currently advised that marketing should be concluded in December although regular monitoring of fruit condition will help determine more precisely the termination dates for particular consignments.
  • The life of Cox apples treated with SmartFreshSM and stored in CA conditions is limited by the development of core flush and flesh breakdown.
  • The termination month for treated fruit is set at January but it may be possible to extend storage of some consignments, particularly in years where climatic conditions have conferred a low potential for core flush and low temperature breakdown.
  • It is possible to make a general assessment of risk based on seasonal weather (Johnson and Ridout, 1998) but careful monitoring of the condition of the stored fruit is required to determine when to conclude storage.

 

The storage of SmartFreshTM-treated Cox beyond January

Growers wishing to extend the storage of SmartFreshSM-treated Cox beyond January are advised to store in CA conditions of 1.2% O2 and <1% CO2 and to ensure that fruit temperature is above 3.5oC in all parts of the store.

  • Carbon dioxide levels should remain below 1% for the entire period of storage i.e. from the day of sealing the store.
  • The practice of allowing carbon dioxide levels to rise initially after store loading is to be avoided.
  • In previous work pre-treating Cox apples with high concentrations of carbon dioxide for 15 days prior to low ethylene, low oxygen storage increased core browning and flesh breakdown (Stow, 1990).
  • In view of the general heightened sensitivity of SmartFreshSM-treated apples to carbon dioxide and low storage temperatures it seems sensible to adopt the strategy suggested for storage beyond January until further work can be done to optimise store environment parameters for maximum storage life of Cox.

 

 

Bramley’s Seedling – benefits

The effect of SmartFreshSM in retarding scald development is the most commercially significant effect since it makes possible the storage of Bramley without the post-harvest application of DPA. Bramley apples treated with SmartFreshSM and stored in conventional ventilated CA conditions (9% CO2 + 12% O2) should remain free of scald until March and those stored in scrubbed low oxygen (5% CO2 + 1% O2) should remain free of scald until July.

  • SmartFreshSM application consistently improved retention of firmness and reduced weight loss in store.
  • SmartFreshSM application provided greener, more acid fruit that were less susceptible to superficial scald and bitter pit.
  • Occasional beneficial effects of SmartFreshSM application included higher soluble solids in the fruit and reduced incidence of senescent breakdown and core flush.
  • Greatest effects of SmartFreshSM application were achieved on fruit picked at the correct stage of maturity for long-term storage.
  • Growers should continue to select for long-term storage those orchards that comply with recommended standards for fruit mineral analysis.
  • Regular and rigorous monitoring of the condition of fruit from store is essential and should include a shelf-life test to provide an indication of scald potential.

 

There is significant orchard variability in the quality of Bramley apples treated with SmartFreshSM (Johnson, 2008) which demonstrates the need to maximise storage potential through attention to pre-harvest factors (see Sections 1, 2 and 3).  To minimise scald risk in Bramley there should be no more than 3 days between picking and application and fruit should stored in a scrubbed low oxygen regime.

 

Bramley’s Seedling – constraints / limitations

Bramley apples not treated with DPA after harvest are susceptible to external CO2 injury when stored in recommended CA conditions.

  • It is necessary to delay the establishment of CA conditions where DPA is not used in order to alleviate the problem (Johnson et al., 1998).
  • Application of SmartFreshSM without the use of DPA caused CO2 injury in Bramley apples stored in 5% CO2 + 1% O2 (5/1) despite a 10-day delay in establishing CA conditions.
  • For SmartFreshTM treated fruit, it is recommended that the delay in establishing CA conditions is extended to 21 days.
  • During this period the oxygen concentration in 5/1 stores can be allowed to decline to 10% but the CO2 concentration should be scrubbed to <1%.

 

Post-harvest application of DPA should negate any risk of CO2 injury in SmartFreshSM-treated fruit and eliminates the need to delay establishment of CA conditions.

  • Delay in establishing CA conditions would normally be considered to conflict with best practice but it is necessary to ameliorate the risk of CO2 injury in Bramley apples not treated with DPA.
  • The consequences of any delay in terms of reduced storage potential / quality are minimal in SmartFreshSM-treated fruit as the ethylene production and ripening processes are slowed immediately after application.

 

Gala (and clones) – benefits

  • SmartFreshSM application consistently improved retention of firmness of air-stored fruit and virtually eliminated softening in CA-stored fruit.
  • SmartFreshSM application reduced weight loss in air-stored fruit.
  • SmartFreshSM suppresses the development of skin greasiness.

 

Gala (and clones) – constraints / limitations

  • No adverse effects of SmartFreshSM application on CA-stored (<1% CO2 + 1.2% O2) fruit.
  • SmartFreshSM application aggravated core flush and flesh breakdown in fruits stored in air at 0-0.5oC for 180 days. The storage of SmartFreshTM-treated fruit in refrigerated air should be terminated in January.

 

Egremont Russet – benefits

  • SmartFreshSM application improved the quality of fruit stored in air and CA conditions.
  • Fruit treated with SmartFreshSM prior to air storage for 90 days remained firm and free of scald and other disorders. However, extending storage in air to 180 days proved too long for SmartFreshSM-treated fruit with fruits being affected by rotting, scald and internal disorders.
  • The storage of SmartFreshSM-treated fruit in refrigerated air should be terminated in December.
  • SmartFreshSM application improved the firmness and reduced the development of breakdown and core flush in fruits stored in CA (5% CO2 + 3% O2) for 180 days. Termination dates for CA-stored fruit are similar for fruits treated or not treated with SmartFreshSM .
  • Since Egremont apples produce very high levels of ethylene the application of SmartFreshSM should be carried out as soon as possible after harvest and preferably within 3 days.
  • Where SmartFreshSM has been applied to commercial stores of Egremont Russet improved control of bitter pit was evident in fruit picked at the mid-point of the harvesting ‘window’ and stored under appropriate CA conditions.

 

Egremont Russet – constraints / limitations

  • There are concerns about the flavour quality of early-picked SmartFreshSM-treated fruit removed from CA storage before Christmas.
  • Consequently SmartFreshSM should not be used on early-picked fruit for pre-Christmas marketing.

 

Other dessert cultivars of apple

Only limited research has been carried out at EMR on other dessert cultivars although commercial experience of the effects of SmartFreshSM application is increasing. Lack of response in some of these preliminary trials may be due to harvesting fruit too late or removing fruit from store too early when untreated fruit may not have softened sufficiently to establish any potential firmness differences. For the latest information on the use of SmartFreshSM on UK-grown apples contact the supplier, Landseer Ltd.

 

Jonagold, Idared and Fiesta

  • CA-stored fruit responded well to SmartFreshSM application in terms of firmness retention.

 

Spartan and Meridian

  • No significant response to SmartFreshTM application in fruit stored in CA for 90 days at EMR.
  • However, in commercial SmartFreshSM applications carried out over the past four years a firmness benefit was found in both varieties.

 

Braeburn

  • Although Braeburn responded well in terms of firmness retention, SmartFreshSM application induced core flush in 75% of fruits.
  • Since development of core flush currently limits the storage life of CA-stored Braeburn. It is clear that SmartFreshSM application cannot be recommended for this cultivar.

 

Empire

No research has been carried out in the UK but it is clear from work done in the USA and Canada that SmartFreshSM application exacerbates the risk of external CO2 injury.

  • It appears that SmartFreshSM application extends the ‘adaptation’ period between harvest and establishing CA conditions (Razafimbelo et al., 2006) that is necessary to eliminate the risk of CO2 injury.
  • In response to the heightened risk of CO2 injury due to SmartFreshSM application, it is recommended that the CO2 concentration for CA-stored Empire apples is maintained below 0.5%.
  • Successful commercials applications of SmartFreshSM have been made to Empire in the UK.

 

Other traditional dessert cultivars

The following cultivars were reported as showing a firmness increase following SmartFreshSM application when stored in air until Christmas (Tully, 2003):

Lord Lambourne, Ribston Pippin, Kidds OrangeRed, Elstar, Chivers Delight, Ashmeads Kernel, Falstaff, Blenheim Orange, Jupiter and D’Arcy Spice.