Munich - Strawberries in January, apples in May: according to 40 per cent of consumers interviewed in a current TÜV SÜD survey, the traditional time of harvest no longer seems to play a role in the availability of many types of fruits and vegetables in Germany.The respondents stated that for them, enjoying fruits and vegetables all year round and not just in their season was very important or important.TÜV SÜD’s experts explain how the ripening process can be speeded up and how consumers can best store and handle fruits that have undergone controlled ripening.
Supermarkets offer a large range of fresh fruits and vegetables throughout the year. In TÜV SÜD’s food safety consumer survey, just under 40 per cent of respondents indicated that for them, enjoying fruits and vegetables all year round and not just in their traditional harvesting season was important. “The fact that many types of fruit are offered fresh even in late winter is due to the controlled ripening process", explains Dr Andreas Daxenberger, food expert at TÜV SÜD.
But what does ‘controlled ripening’ actually mean? What has to be observed in the storage of fruits and vegetables that have undergone controlled ripening, and when are these fruits best for consumption? Depending on their origin, avocados, mangoes, papayas and other tropical fruits are offered in supermarkets all year round, for example. However, when we buy them, many of these fruits are still rock-hard and take a long time to soften even when we keep them at home. Some of these fruits are not sweet when we buy them, yet spoil in our kitchens within a few days before ripening.
Ripening gas – a trick of nature
It’s all in the biology. Some fruits, including avocados, kiwis and bananas but also peaches, tomatoes and apples, produce large amounts of ethylene while ripening. As ethylene is a gas that simulates the ripening process, they continue to ripen after they have been harvested. Given this, these types of fruit are not harvested when ‘ready to eat’, but when ‘ready to pluck’. Full ripeness is only achieved during transport and storage. However, determining exactly when a fruit is 'ready to pluck' is not always easy. Given this, the fruits sold in the supermarket may sometimes be overripe or not yet ready to eat.
The right level of ripeness at the right time
To offer customers fresh produce that is ‘ready to eat’, supermarkets increasingly sell fruits and vegetable that have undergone controlled ripening. Controlled ripening has been used for bananas for decades. The fresh produce is harvested when it is just ripe enough to be plucked. It is then transported and stored in a controlled atmosphere. By reducing the levels of oxygen the fruits are put into artificial hibernation, thereby interrupting their ripening process. They are not ‘woken up’ until shortly before they are sold, when they immediately start to ripen again. This ripening process is speeded up by storing the fruits for some days at specific temperatures in an atmosphere to which the ripening gas, ethylene, is added. Thus the fruits ripen, become ‘ready to eat’ and can be enjoyed immediately after buying. Studies on the nutritional value of mangoes have showed that the nutrient content of mangoes after controlled ripening hardly differs from that of naturally ripened fruits. However, fruits that are plucked too early will not be able to build sufficient flavours and nutrients during post-harvest ripening.
Tips for consumers
“For consumers, this means that fruits and vegetables that underwent controlled ripening do not keep very long. They should therefore be consumed as quickly as possible", recommends Daxenberger. Many of these fruits do not tolerate cold temperatures either, so that storage in the fridge is a no-no. In addition, each type of fruit produces different amounts of ripening gas or shows differing levels of sensitivity to it. Given this, fruits that produce ethylene (e.g. stone fruits and pome fruits, melons, bananas and tomatoes) should always be kept separate from ethylene-sensitive fruits and vegetables (e.g. aubergines, cucumber, leafy salad greens, parsley, cauliflower, carrots, pumpkin).