New research: Keeping fruit fresher for longer
Professor Zora Singh

New research: Keeping fruit fresher for longer

Angela Youngman

Keeping food fresher for longer is one of the key issues facing the produce industry.  Two new initiatives involving innovative university research in Australia and the UK could well revolutionise the situation. Produce Business UK takes a closer look. 

At Curtin University in Western Australia, horticultural researcher Professor Zora Singh and organic chemist Dr Alan Payne have devised new compounds called ethylene antagonists which slow down the process that leads to spoiling. The researchers believe that it has the potential to substantially reduce the billions of tonnes of food wasted every year because of spoilage. 

“I started to think how could I make a compound that is easier to make, easier to use and I came up with these compounds that Zora was happy to test on fruits,” says Dr Payne. 

“The way these compounds work is that they don’t reduce the production of ethylene, they prevent the fruits and vegetables from perceiving ethylene. Every fruit has a receptor that ethylene binds to. What we’re doing is we’re masking those receptors.

“The beauty of these compounds is that we can apply them in the production phase, and they are more user friendly,” adds Professor Singh. 

The duo claim their ethylene antagonists are extremely versatile and can be used in a variety of ways; before and after harvesting as a solid or liquid, dipping, waxing and fumigation. The ethylene antagonists are created in the form of solids and liquids, ensuring they can be easily used at any point in the production process.  

They are said to be most effective when applied prior to the beginning of the ripening process. Although the compounds are environmentally friendly, they are not registered to be used in organic produce.

Dr Alan Payne and Professor Zora Singh

These new ethylene antagonists are said to be suitable for a wide range of fruits and vegetables including apples, nectarines, plums, tomatoes, bananas, pears, papaya, mangoes, peaches, apricots, oranges, lemons, limes, grapefruit, tangerines, kiwi fruit, pineapple, persimmons, avocados, melons, berries, cherries, most leafy green vegetables such as lettuce, spinach, cabbage, vegetables such as carrots and potatoes, onions, garlic, asparagus, sweetcorn, broccoli, peas and herbs such as basil and oregano.

An additional advantage possessed by the new ethylene antagonists is the fact that they can allow producers to control the rate of development in the fields, thus protecting from plant stresses. 

Zora and Payne say that, “Ethylene is not only a ripening hormone but is also involved in plant developmental and stress responses. As these compounds block ethylene action, they retard development of flower and leaf abscission and have the potential to alleviate ethylene-mediated stress responses.”

Search for partners 

The discovery of ethylene antagonists has already won Payne & Singh a Curtin University Commercial Innovation Award and a patent has been filed, while potential partners to commercialise the technology are now being sought.

“The research being conducted by a group in Australia on ethylene antagonists looks very interesting and could be worth trialling in the future. New products like this need to be fully evaluated by the appropriate regulatory authorities before they can be used commercially. Ethylene, whilst important, is only one element in a complex interaction of many factors. Ethylene antagonists used in combination with the new MAP techniques might further extend shelf life. We shall be keeping an eye on these developments closely,” says Keston Williams, technical director Barfoots. 

New Research into MAP techniques

It is these MAP techniques that are coming under scrutiny in another research project that has just begun. Cranfield University is working with sustainable technologies company Johnson Matthey on the next generation of modified atmosphere packaging with the aim of extending shelf life.

The three year project started last October and has received more than a quarter of a million pounds in funding (£275,733) from the Biotechnology and Biological Sciences Research Council (BBSRC) and Innovate UK.

The aim of the researchers is to create innovative, cost effective solutions to allow fresh produce to keep longer at optimum freshness.  Attention is being focused particularly on the control of respiratory gases so that it can cope with the way in which fresh produce changes its physiology during storage and this can lead to suboptimal conditions. This can have a major impact on the condition of fruit and vegetables.

“This new research, now underway at Cranfield, is a very welcome development. The fresh produce industry is constantly trying to reduce waste throughout the supply chain, extend the seasons (especially the UK), deliver high quality produce to the consumer with long shelf life, adds Williams. 

“Current MAP (modified atmosphere packaging) technology addresses some of these issues, but it still needs further optimisation.  My expectations are that this project will be able to deliver this optimisation, together with the benefits to both supply chain and consumer.”

“Current MAP systems are optimised to a typical respiration rate within a typical temperature range, which is great if you have a perfect storage environment with a perfect crop. Step outside of these ‘typical ranges’ and the MAP doesn’t perform as well as it could.  I am hoping this research, coupled with EMAP packaging, will be able to resolve these current problems.”

Consumers now expect to have fresh produce available throughout the year. Consequently produce has to be stored for longer periods in order to provide that availability, and out of season produce has to travel long distances from overseas growers.  Losses due to deterioration during storage from grower to retailer can be as high as 40 percent.  Farmers lose money and produce has to be destroyed.  To replace this lost produce, more items have to be imported from all over the world which can substantially increase food miles and overall costs.

“We can already extend the post harvest quality of fresh produce through current modified atmosphere packaging (MAP). It’s performance is often limited, however, by an inability to respond to the changing physiology of the produce, leading to the development of suboptimal gas conditions. The packaging would benefit considerably if it is made flexible so that it responds to the changing physiology of the produce,” says director of environment and agrifood at Cranfield University, Professor Leon Terry.

Improving MAP performance

The research project will investigate technologies that can extend shelf life beyond the level of refrigeration. According to the project outline ‘Current methods to store fresh produce rely on a combination of refrigeration and MAP. The packaging films are often more permeable to CO2 than to 02 but if micro perforations are added, the permeability to both is similar. The control of temperature, humidity, 02, C02 & ethylene concentrations can al help extend the produce’s shelf life.  EMAP packaging such as Xtend can control 02, C02 and humidity to a certain degree, but there are instances where EMAP alone is insufficient.’

The biggest problems are encountered with fresh produce that does not react well to very low levels of CO2, packaging which is subject to temperature abuse or where the EMAP conditions take a week or more to reach optimum levels.

Typical examples are berry fruits such as grapes that can deteriorate during storage. 

Existing methods being used to store grapes and berries include the use of SO2 releasing pads. These are not fully effective, although the pads allow the produce to be stored for up to three months and the chemicals used are a known allergen. This can result in the flavour becoming tainted, colour bleaching and berry shattering. The researchers believe that creating more effective bulk modified atmosphere packing would be revolutionary.

Another typical problem with existing modified atmosphere packaging relates to asparagus. This is a product that reacts well to modified atmosphere packaging, and better optimisation of the gas compositions within the packaging would enable asparagus to be stored much longer, thus extending the season for UK asparagus.  

Avocados are an example of the problem of coping with low temperatures during shipment and shelf life in the retail outlets at a much higher temperature. To overcome this and extend the shelf life of avocados, the researchers believe there is an opportunity to improve the packaging by the addition of ‘active materials’.  

At present the only active materials applied to fresh produce on a major scale are ethylene scavengers.  These materials work in the same way as a catalytic converter by removing ethylene gases which cause fruit and vegetables to ripen, thus ensuring that they stay in optimum condition loner. 

As a result, researchers will be focusing on methods of developing MAP systems comprising innovative cost effective inserts which can manipulate the internal packaging atmosphere. This would allow ideal gaseous conditions to be kept at optimum levels for prolonged storage and better produce management throughout the supply chain. 

As Professor Leon Terry indicates: “The project will focus on the development of the next generation of modified atmosphere packaging comprising innovative cost-effective inserts which are able to manipulate the internal atmosphere of the packaging.”

Commenting on the two new initiatives, Nigel Jenney, chief executive of the Fresh Produce Consortium says “the industry welcomes research and innovations which can maximise shelf-life and quality for consumers.”





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