Fruit Ripening

More than half of the European population consumes fruit or vegetables daily. Consumers consider them healthy sources of vitamins and fiber. How our fruit and vegetables get into the supermarkets ripe and ready to eat, however, is rarely discussed.

Besides quality, the freshness, color and taste of fruits and vegetables are the main criteria for purchase. An appropriate degree of ripeness plays an essential role: If the fruit is not yet ripe enough for consumption, the buyer has to ripen it at home for a few more days. If the fruit is already overripe, both the appearance and the taste are impaired. With the right degree of ripeness at the time of sale, unnecessary food waste can be avoided. In times of climate change, avoiding overproduction and food waste is of great importance.

Fruits Influence Each Other

As with many processes in the human body, the ripening of fruits is also influenced by hormones, the so-called phytohormones. In addition to fruit ripening, these hormones also influence the growth and death of plant parts and the development of flowers.

The most important hormone for ripening is ethylene (C2H4). When food ripens, the concentration of emitted ethylene increases. The fruit itself also influences the amount of ethylene emitted. There are fruits that emit a lot of ethylene, such as apples, and those that emit less, such as bananas. The ethylene emitted by one fruit thus also causes other fruits to ripen more quickly. Something to consider when storing fruit, both industrially and in private households.

Targeting the degree of ripeness with gases

French scientist Jacques Étienne Bérard was already investigating the effect of gases on the degree of ripeness of fruit at the beginning of the 19th century. He discovered that already harvested fruits absorb oxygen (O2) and release carbon dioxide (CO2).

By removing oxygen, it was possible to slow down the ripening of the fruit. This made it possible to transport the fruit without it becoming inedible in the meantime. Today, knowledge of these ripening gases is used for early harvesting and transport to the point of sale. For example, many fruits are harvested in an unripe state and refrigerated while transported to briefly interrupt the ripening process. Once the fruit has reached its destination, ripening is artificially continued or even accelerated, as required. The targeted use of ethylene, but also of acetylene (C2H2) and carbon dioxide, has a precise effect on the ripeness of fruit for consumption. For continuous monitoring of these ripening gases, optical measurement techniques such as non-dispersive infrared spectroscopy (NDIR) are usually used. When using a broadband infrared source with high emission power, such as the one from Axetris, and a multi-channel detector, several gases can be measured simultaneously. This means that the measurement technology can be used flexibly, regardless of the ripening gas used.