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201912 Fresh Quarterly Issue 7 02 Past Research On Packaging Options
Issue SevenDecember 2019

Past research on packaging options

Past and present project. By Dawie Moelich and Anna Mouton.

The Post-Harvest Innovation Programme and the Deciduous Fruit Producers’ Trust — now Hortgro — funded a project on internal packaging for Golden Delicious and Pink Lady apples, Bon Chrétien and Forelle pears, and Sapphire and Larry Ann plums from 2008 to 2010. Dawie Moelich, then of ExperiCo, tested various liners in combination with plastic crates and cardboard boxes.

Forced-air cooling rates were faster in the plastic crates than in the cardboard boxes. Fruit also cooled four to eight times faster without liners. Faster cooling was beneficial for Bon Chrétien but had no benefit for the other cultivars.

Fruit lost the most moisture in the plastic crates and when packed without liners. The researchers concluded that packaging liners are necessary as moisture barriers in most cases. With Bon Chrétien, 20µm bags resulted in yellower fruit. A significant and surprising finding was that 20µm LDPE — low-density polyethylene — bags had similar performance to 37µm and 60µm LDPE bags when tested in the apples and Forelle pears.

Modified atmosphere potential of LDPE liners

The South African fruit industry used the beneficial effects on pome fruit of modified atmosphere packaging for decades. The original 37µm LDPE bags were mainly utilised for the preservation of green skin colour of Golden Delicious and Bon Chrétien, whereas the 60µm LDPE bags were used both for the preservation of green colour and preventing the development of greasiness in Granny Smith. Notably, these original liner types were successfully introduced into the ‘deeper’ packaging formats — MK4 and MK6 telescopic cartons, which dominated the industry at the time.

In this project we used MK9 or similar dimension packaging for the pome fruit studies. No major quality differences resulted from polyethylene bags of different thickness in some of the pear and apple populations. Therefore, this provides an opportunity for reduction of material with optimum picked and packed fruit.

However, a concern was raised that the transition of the original modified atmosphere packaging technology from mainly MK4 and MK6 to MK9 packaging has not occurred optimally. The specifications of the commercial bags used at the time may also have been compromised.

Although oxygen and carbon dioxide levels were not specifically studied in this programme, the atmospheric gas levels were occasionally monitored towards the end of the cold storage period. In the 600 x 400 mm pome fruit packaging, the carbon dioxide levels were frequently below 1%. This indicated that the LDPE liners, as tested in MK9 format on the pome fruit, were likely to have minimal impact on maintenance of green skin colour by means of atmosphere modification, even if the moisture barrier properties of the film are beneficial.

It was also evident that the carbon dioxide levels in packaging with more free headspace were lower than in the fuller packed formats, indicating that the “folding” of the bags is important, as has been previously reported.

Since the requirement for some form of moisture barrier was clearly evident for most of the fruit populations studied, sacrificing the modified atmosphere ability seems to be a significant waste of a potential quality maintenance benefit of polyethylene liners, especially for cultivars which are not sensitive to elevated carbon dioxide levels. For cultivars with specific requirements, where it is still potentially beneficial to utilise the modified atmosphere potential of LDPE for quality maintenance, the consistency of quality and dimensions of polyethylene liners and means of application require continual attention.

More information is available on the Post-Harvest Innovation Programme website.

The rise of edible coatings

One way to gain the advantages of plastic without the drawbacks is to coat fruit in waxy materials called edible coatings. The fruit’s natural wax is removed, and a synthetic coating applied, limiting moisture loss, and protecting the fruit from spoilage organisms.

Edible coatings are already common in both Chile and the United States. New Zealand is also increasingly turning to waxes, although they use less plastic than South Africa — New Zealand fruit is exported in bulk and bagged in the country of import.

Hortgro Science has been funding trials of edible coatings on stone fruit. Trials done on plums showed that certain edible coatings could reduce shrivel significantly. Dr Ola Fawole presented the latest on this research at the recent Hortgro Science Symposium. Read a summary of his presentation in the July 2019 issue of Fresh Quarterly.

Two new plastics projects get under way

Hortgro Science has contracted ExperiCo to conduct a knowledge review of plastic use in the pome and stone fruit industries. The review will include lessons to be learnt from other local industries. It will cover the entire value chain from packhouses to retailers with special consideration of the requirements of our export markets. Close attention will be paid to trends in other exporting countries such as Chile. The knowledge review is a one-year project and is seen as a starting point for further research.

The second project is a collaboration between the Agricultural Research Council and ExperiCo and will involve packaging trials. Researchers will test the efficacy of a plastic cover that encloses an entire pallet. The current standard is a plastic liner in each box of fruit. Covering the entire pallet may reduce the total amount of plastic as well as facilitating recycling. Initial trials will be conducted with Royal Gala apples.

The packaging trials will also revisit the use of different liners for Forelle pears. Previous research showed that 20mm polyethylene bags have the potential to replace the standard 37mm bags. The new project will focus on FEMA — Forelle early market access — pears. A reduction in liner thickness holds the promise of decreasing total plastic use.

Results from the first year of packaging trials will determine the experimental design for the second year of the project.

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