Hyperspectral imaging selects the best fruit

Wasted food amounts to loss of earnings if you're a retailer selling produce. Damaged or rotting fruits and vegetables are routinely thrown out when they can no longer be sold. It is therefore imperative that the retailer buys produce with a good shelf life. But knowing which ones will stay fresh the longest is not always apparent from a visual inspection. Bruised fruit may show no signs of damage on the surface but will be the first to rot. Scientists from the Fraunhofer Institute for Photonic Microsystems (IPMS) in Germany have been working on an inspection tool that uses hyperspectral imaging to reveal such information.

Hyperspectral imaging involves illuminating a sample with broadband light and recording the intensity variations across the range of wavelengths in the reflected spectrum. It's like having eyes that can not only detect the colour of an object, such as the rosy red of an apple, but that can discern all of the individual colours that are reflected and that combine to form that single colour. Because we don't see the constituent colours, we miss out on valuable information. In this case, the information we can't always perceive with our eyes is damage to fruit - until the rot sets in a short time later.

Commercial hyperspectral imaging systems can be prohibitively expensive, so the IPMS researchers developed a system which could be sold far more cheaply. They did this by scaling down the detector from a typical two dimensional sensor array, which detects both position and wavelength, to a linear one which is sensitive to just the wavelength intensities and relies on a moveable mirror to scan the sample. A broadband infra-red light source is used to illuminate the sample and the mirror, which contains a diffraction grating, splits the reflected light into its component wavelengths, which are then detected by the sensor.

With such a device installed in a production line, it should be possible to select the highest quality produce, which will have longer and more guaranteed shelf lives. The poorer quality produce could be discarded and, instead arriving on the supermarket shelves, would be sent elsewhere for processing.

Source: Fraunhofer-Gesellschaft