Issue 26: Modified Atmosphere Packaging

Issue 26
January/February – 1996
Story Title: Modified Atmosphere Packaging

At the Institute for Horticultural Development in Victoria, research into modified atmosphere packaging has resulted in the development of successful commercial applications.

Modified Atmosphere Packaging (MAP) of fresh horticultural produce is an attractive and simple concept. It uses the gases produced and consumed during the respiration of fresh produce, that is carbon dioxide (CO2) and oxygen (O2) respectively, to produce a favourable atmosphere in a specially designed polymeric film package. If the package has the correct permeability to CO2 and O2, a unique atmosphere for that product is created, usually enriched in CO2 and reduced in O2. This favourable atmosphere slows the metabolic activity of the produce to a very low level, and thus MAP enables the storage of highly perishable produce for prolonged periods.

The ability to store produce, while retaining its food and nutritional value, increases market flexibility. Industries can add value to produce, by storing it during market gluts and releasing it when demand increases and by branding and differentiating produce as high quality and high value. Exporters can use relatively cheap and available seafreight transport, which increases competitiveness in existing markets and allows access to new markets.

A future, very large use of MAP is for package branded, value added, minimally processed vegetables. MAP is essential for the successful marketing of these products, which are expected to add up to $1 billion to the value of the Australian vegetable industry.

How MAP Works
All fresh produce is alive and must burn up food reserves to keep it alive. The chemical reactions involved are generally termed respiration. In normal healthy plants, respiration involves the uptake of oxygen (O2) by the plant tissue to oxidise food reserves, usually sugars, to produce energy, carbon dioxide (CO2) and water. In simple terms, the energy produced is used to maintain essential life processes, while the CO2 and some of the water are ‘waste’ products and are released to the surrounding environment.

When fresh produce is sealed inside a polymeric (or plastic) film package, respiration will lower the in-package O2 level and increase the CO2 level. A major challenge in designing MA packages, is to match the rate of O2 uptake and CO2 production of the produce, with the O2 and C02 permeability of the package. If a package is well designed, gas levels inside the package will equilibrate within a range which benefits the produce. For most products, the therapeutic range for CO2 and O2 is between 2% and 10%.

However, optimum CO2 and O2 concentrations are product specific and vary enormously between products. Examples of optimum CO2:O22levels are: broccoli 5:2; asparagus 10:10; lettuce 2:2; peaches 6:1.5; pears 2:2; carrots 0:21; blueberries 6:1.5 etc. It should be noted that exact recommendations are rare and often a therapeutic range is quoted, as optimum gas levels can vary according to cultivar or genotype, production area, harvest maturity and a number of other factors.

If the optimum atmosphere for a product is achieved, its storage life can be increased by many times that which can be expected using conventional refrigerated air storage. Elevated CO2 and reduced O2 levels slow quality loss in a number of ways. The principal effect is usually considered to be in suppressing respiratory activity. As a rough rule of thumb, the post harvest life of fresh horticultural produce is inversely proportional to its storage life. That is, the lower the respiration rate, the longer food reserves are conserved and the longer life processes can be maintained. This effect is often termed ‘putting the produce to sleep’. However, there are a number of other benefits. High CO2 and low O2 atmospheres can:

1.Block the mode of action and biosynthesis of ethylene, a ubiquitous plant hormone which promotes aging and senescence.

2. Reduce rots by directly inhibiting the growth of pathogens and by maintaining the health and integrity of the plant tissue, which reduces its susceptibility to infection.

3. Slow yellowing of green tissues by preventing chlorophyll degradation

4. Maintain the food and nutritional value and flavour of produce by slowing the loss of food reserves, particularly sugars, inhibiting the loss of labile vitamins such as vitamins C and A, and by slowing the accumulation of undesirable secondary metabolites in the plant’s tissues, such as free ammonia.

5. Slow cell membrane degradation and loss of cellular compartmentation and function.

6. Inhibit discolouration of cut surfaces.

A well designed MA package is a discreet, self sufficient, fully portable (at least up to the pallet level) ‘pseudo’ CA (Controlled Atmosphere) storage unit, which can provide significant benefits to fresh produce in reducing quality loss and extending storage and market life. MAP provides the horticultural industry with a means to add value to their crops by expanding existing and developing new domestic and export markets.

MAP Research at IHD Knoxfield
At the Institute for Horticultural Development (IHD), Knoxfield Victoria, research into modified atmosphere packaging has been continuing for a number of years under team leader Bruce Tomkins. With funding from both government and industry, the team has met with considerable success in developing commercial applications of MAP. Recently, they were awarded the Daniel McAlpine Award for Outstanding Advances & Excellence in Science, by the Victorian Government.

IHD’s MAP team in collaboration with industry partners, has successfully introduced commercial MAP systems for the following crops: broccoli, cauliflower, celery, sweet corn, artichokes, parsnips, leeks, cherries, sugar plums, Kiwi fruit, nectarines, lettuce, Japanese and European plums, bananas, blueberries, Packham, WBC and Bosc pears, lettuce mixes, chestnuts, and stirfry and soup mixes. It is estimated that the availability of MAP has already increased the value of horticultural exports by at least $10 million per annum. At the launch of a large MAP contract research project between IHD, CSIRO and ANL Limited, the then Minister for Primary Industries, Mr Simon Crean, stated that the development of MAP will add $300 million per annum to the value of Australian horticultural exports.

Interaction with CSIRO
In developing commercial applications for modified atmosphere packaging, IHD’s MAP team collaborated with other research and industry institutions to form a multi-disciplinary team. A collaborative research program with the CSIRO resulted in an early research milestone – the development of a predictive mathematical model for MAP applications. The model, developed jointly with the CSIRO’s Division of Materials Science and Technology, has been shown to be a very effective and valuable tool in predicting the gas transmission requirement of specific MAP applications under a wide range of environmental conditions. Application of the model has speedup the development of packaging applications by eliminating much of the time consuming, empirical research required to select suitable packages, if this information was not available.

Interaction with ICI and CP
One MAP technology developed by IHD in collaboration with ICI Films is the ‘LifeSpan’ range of packaging. IHD developed a simple technique for altering film permeability and provided ICI with expert advice and research on the horticultural and postharvest physiological factors which need to be accounted for in the design of MAP. This information and the ability to easily alter film permeability to account for the needs of individual products, have been the major reasons for ‘LifeSpan’s’ success.

Both the technology and the ‘LifeSpan’ team were recently sold to Containers Packaging (CP), a subsidiary of Amcor. IHD has an on-going collaborative research agreement with CP, and the Institute receives royalty payments for all ‘LifeSpan’ products sold. At present, ‘LifeSpan’ packaging is commercially available for broccoli, cauliflower, celery, sweet corn, artichokes, parsnips, leeks, cherries, sugar plums, kiwi fruit, William pears, nectarines, lettuce and a range of Japanese and European plum cultivars. Packages for approximately 15 other crops are currently being developed, with some undergoing commercial trials. All these packaging applications are for carton lots of produce. Orders for ‘LifeSpan’ packaging are now being received from overseas and a recent consignment of 200,000 bags was sent to Europe.

Interaction with ANL Ltd and CSIRO
Collaboration with the CSIRO Division of Materials Science and Technology, and their team of polymer chemists and materials engineers, has provided the ability to select and manufacture new films, specifically designed for MAP according to the model’s predictions. CSIRO has patented the technology to manufacture MAP films and the license has been purchased by ANL Limited. IHD conducted a very large contract research project with ANL to commercialise packaging systems using the range of new MAP technologies developed.

In developing these new packaging systems, the MAP team follows a structured experimental protocol, starting with a critical review of published literature. There are a number of steps involved:

Determine the optimum storage environment.
Determine the product’s physiological response to this environment during prolonged storage.
Measure the product’s respiration rate.
Mathematically model the packaging application to predict the film permeability requirements.
Design and test prototype packages in the laboratory and determine the maximum storage and market life.
Test the best prototype package(s) in a land-based seafreight container trial to simulate export by sea.
Conduct full scale seafreight shipments under full commercial conditions.
A member of the MAP team travels to the market to examine the quality of the produce on arrival and exposes the produce to a simulated marketing phase to ensure it has an adequate shelf life after shipment.
A full quality assurance (QA) protocol is developed for the postharvest handling and packaging of the product.
The packaging system is produced commercially and sold with the QA protocol.

This research program has produced commercial packages for broccoli, Packham’s Triumph pears and bananas. All have been very successful under commercial conditions and are being used to export these products by sea to Japan, Hong Kong, Singapore, Malaysia, the Middle East and Greece. Other packaging applications which have been developed to commercial testing include citrus, plums, apples, lettuce, cauliflower, broccoli florets and WBC and Bosc pears.

Interaction with Growers, Exporters and Processors
A range of other packaging applications has been developed from pallet to consumer pre-packs. Bulk packaging systems have been developed for blueberries, cherries and chestnuts. Pre-packs have been developed for herbs, asparagus and a range of minimally processed vegetables, including salad, stir-fry and soup mixers. MAP is an essential requirement for minimally processed vegetables and the success of the industry. It has been estimated that minimal processing will add up to $1 billion dollars to the value of Australia’s vegetable industry over the next 5 to 10 years.

Specific Industry Developments
Below are a few examples of industry developments as a result of the IHD MAP team’s research work.

Woolworths have insisted to growers that all broccoli delivered to their stores in New South Wales, Queensland and a large proportion in Western Australia has to be in ‘LifeSpan’ packaging. This has reduced costs by at least 25% and all components of the package are fully recycled.

Previously, expanded polystyrene packaging was used and its disposal caused substantial problems and was very costly. Now Woolworths are paid by the recyclers for the used cartons and carton liners.

Sea-freight exports of broccoli to Japan are increasing exponentially. Due to the availability of MAP, two new export groups have formed in Victoria, one based in Warrnambool and one in East Gippsland. They are exporting six 20-foot container equivalents each week, which will amount to approximately 1400 tonnes per year with a value of around $1.5 million per annum (after freight). This is expected to increase substantially. Also, supplying a new export market has reduced the social and economic impact on East Gippsland growers of the closure of the Gardenland processing factory.

This packaging system, which was developed entirely by the MAP team, is applied at the pallet level, is made by the growers themselves and is extremely inexpensive.

Blueberries are a very seasonal crop and in the past, growers have had to sell their crop during the middle portion of the season at below break-even prices. Now, they have the means to store fruit for up to 12 weeks during market gluts. One larger grower who stored most of his crop for the last 3 years, has more than doubled his total income.

As well as storing berries, Corindi Farms now use MAP to export to Europe. They estimate the size of this new market at approximately 200 tonnes or $3 million after freight costs.

Over the last two seasons, approximately 2 million dollars worth of cherries have been sea-freighted to Hong Kong, Singapore and Taiwan with few out-turn problems. The Taiwan market has tremendous potential and the capacity to take a large increase in volume.

In addition, some cherries have been stored domestically to increase the length of the season.

The MAP team is one of the few teams world wide who have had a high level of success in developing MAP applications for the horticultural industries. This has had a significant impact in reducing wastage, adding value and increasing exports. According to IHD, a keystone to their success has been a multi-disciplinary approach through effective collaboration and working closely with industry. Collaborators include the CSIRO Divisions of Materials Science and Technology, Horticulture and Food Research, the Western Australian Department of Agriculture, AFISC, growers, packers, exporters, processors, film manufacturers and transport companies.

(IHD’s MAP team is funded by Industry, the HRDC, RIRDC and the Victorian State Government’s Recurrent Funding and Food and Agriculture Initiatives.)