Why do the vegetables, fruit and cut flowers you buy stay so fresh after harvest? It's something that consumers give little thought to. But behind the scenes, Wageningen University & Research (WUR) has been carrying out lots of research to ensure you can munch on juicy apples year-round or enjoy a beautiful bouquet in your vase for weeks on end.
A product's freshness (and how long it stays fresh), shelf life or ripeness at the time of purchase depends on various factors, such as the crop, the time of harvest or the storage or cooling method. The quality of a product is not static: it can be affected at every stage of the process.
Making sure products stay fresh for longer not only benefits the quality of produce in shops, but also means products aren't thrown away when they're still edible. A vast quantity of food is thrown away or not eaten (produced for consumption, but instead processed into something else), with Dutch consumers alone putting several billions of euros of edible food in the bin each year. This waste problem is widespread. It occurs during harvest, storage or transport and even in supermarkets, cafés, hotels and restaurants, and at home.
On 6 October, WUR opened a completely redesigned research facility, equipped with climate chambers and packaging research areas, to support business owners in their efforts to improve the shelf life of fresh produce. The facility has also been kitted out with the latest robots and computer-controlled techniques for visual assessments.
This bundling of expertise is just as important as the facilities. Knowledge about physiology – i.e. the processes in ‘living material,’ which includes vegetables, fruit and flowers – and characteristics relating to quality and shelf life play an equally crucial role as the ability to develop computer models. As WUR has all this expertise on-site, it can develop methods that use sensors (or automated robots) to quickly, accurately and consistently measure and predict quality and shelf life – all without damaging the produce.
When is an avocado ripe?
We have all tried one of those ‘ready-to-eat’ avocados. As avocados do not ripen until they've been harvested, the fruit – a native of South America – is first harvested from the tree before being shipped to the Netherlands in a cooled environment a few weeks later. Once ripened at room temperature, the fruits are laid out in the shop.
But that's not the end of the story, says Wageningen-based research Eelke Westra. Avocados can be very temperamental. ‘Each avocado ripens differently. While one may ripen quickly, the other one may take days.’ WUR was conscious of this problem and developed assessment methods, such as a measurement of a fruit's hardness, that can predict when an avocado is ripe and at its best. WUR also carries out similar research on other tropical fruit.
Plants are very sensitive to temperature. For instance, chrysanthemums (Dutch) seem to be at their happiest when they're stored at fridge temperature (5°C) immediately after harvest. They also need to remain at this temperature until they're been put out in the shop. In contrast, the orchid Phalaenopsis (Dutch) prefers warmer climes. Growers, traders and transporters need to make sure their premises and processes cater to these different preferences to make sure the products are of the best possible quality.
Packaging fresh produce in the right sort of protective packaging can also reduce spoilage and triple a product's shelf life. An important consideration is that many fresh products continue to ‘breathe’ after harvest: they absorb oxygen and release carbon dioxide, water and heat. This process converts starch into sugars, which in turn are made into energy. We can make sure products stay fresh for longer by tailoring the packaging to this respiration behaviour, such as by creating very small holes. On the other hand, fresh meat, fish, cheese and cooked products do not breathe. This means they stay fresh for longer in the packaging that has a specific air composition. Het Klokhuis, a Dutch children's TV programme, recently aired a programme about smart packaging (Dutch).
Mobile research facility
Wageningen has also developed a unique mobile research facility (Dutch) for this type of research. This ‘Cool container’ was unveiled in August. From the outside it looks like a shipping container, but inside it houses a high-tech research space complete with climate chambers and modern measuring and control equipment. The mobile facility means research on the quality and storage of fresh produce can be carried out anywhere in the world. This will be a great benefit for companies and governments in developing countries. Having products with a longer shelf life will help to reduce food waste and improve export opportunities.
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