Atmosphere regulated by photoacoustic sensors during the transportation of fruit

© Fraunhofer IBP

The transportation of fruit from remote fruit farms to local supermarkets is a long-lasting procedure in most cases, especially if tropical fruit is involved. The ripening process, however, is continued during storage and transportation. If the fruit is overripe, quality is deteriorated. This can entail high losses between 50 and 70 percent after the harvest according to the duration of storage and transportation as well as predominating conditions during this period of time. The ripening process, however, is slowed down by refrigeration and by storing and transporting fruit in refrigeration containers. This kind of refrigeration, however, requires high energy consumption and the costs have a great effect in form of a noticeable increase in the price of fruit.

In cooperation with researchers at the University of Campos in Brazil (UENF) investigations were conducted on the question how the ripening process can be specifically regulated by precise monitoring in order to reduce energy consumption, to prolong the transportability of the fruit, and to minimize costs. The specific emission behavior of the fruit serves as an approach for this kind of monitoring. During the ripening process they emit certain gases. Especially ethylene is a gaseous hormone of plants which causes an auto-catalytic process during the ripening process. To allow the detection of this indicator of ripeness of the fruit during transportation in a first step suitable photoacoustic sensors were developed. They use the effect that gaseous molecules, if they are 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 the degree of ripeness of the fruit can be assessed by this information, and the optimal storage atmosphere in the container can be regulated.

The next steps of common research are already defined. Since the optimal atmosphere is different for the various types of fruit and also dependent on temperature the aim is now to determine parameters of the different types of fruit and to develop adequate photoacoustic gas sensors. The advantages to detect even minimal gas concentrations with high selectivity and by cost-efficient technique are a good reason to put this method into practice.