Controlled Atmosphere with Photoacoustic Sensors during the Transportation of Fruit

Test setup Photoacoustic Sensors
© Fraunhofer IBP
Test setup Photoacoustic Sensors.

The transportation of fruit from distant fruit farms to the local supermarkets usually takes a long time, especially if it is tropical fruit. The ripening process continues during storage and transport. However, if the fruits are overripe, they lose quality. This can entail high losses of between 50 and 70 percent after harvesting, depending on the prevailing conditions during this time. The ripening process is therefore slowed down which involves storing and transporting the fruit in refrigerated containers. This kind of refrigeration in turn, requires a lot of energy and the costs are reflected in a noticeable increase in the price of the fruit.

In cooperation with researchers from the University of Campos in Brazil (UENF) investigations were conducted on how the ripening process can be specifically controlled by close monitoring in order to reduce energy consumption, extend the transportability of the fruit, and minimize costs. The starting point for this monitoring is the specific emission behavior of the fruits. During the ripening process they emit certain gases. Especially ethylene is a gaseous hormone of the plants, which causes an auto-catalytic process during ripening. To detect this indicator of ripeness of the fruits during transport in a first step, suitable photoacoustic sensors were developed. They make use of the effect that gas molecules, when excited by modulated laser light, produce a measurable sound emission, the amplitude of which is a measure of concentration. Applied in combination with ethylene and carbon dioxide, this information can help to assess the degree of ripeness of the fruit, and to control the optimal storage atmosphere in the container.

The next steps of the joint research have already been defined. Since the optimum atmosphere differs for the various types of fruit and also depends on the temperature, the aim is to determine the parameters for different types of fruit and develop adequate photoacoustic gas sensors. The advantages to be able to detect even minimal gas concentrations with high selectivity and inexpensive technology provide good reasons to put this method into practice.