PosterPDF Available

Movable external lamp fitted to a hand-held VIS/NIR spectrometer to scan ripening apples on the tree

Authors:

Abstract

To build a hand-held mobile device (operated by one hand), to obtain 'VIS/NIR‘ spatially resolved’ transmission spectra from ripening apples on the tree. To better determine fruit ripening processes, for reduced postharvest losses & more income for the fruit grower.
Movable external lamp fitted to a
hand-held VIS/NIR spectrometer to
scan ripening apples on the tree
Roy McCormick & Konni Biegert
Aims:
To build a hand-held mobile device (operated by one hand), to obtain VIS/NIR spatially resolved’ transmission spectra from ripening
apples on the tree. To better determine fruit ripening processes, for reduced postharvest losses & more income for the fruit grower.
Contact
Roy McCormick, Kompetenzzentrum Obstbau-Bodensee, Schuhmacherhof 6, 88213
Ravensburg, Germany
E-Mail: mccormick@kob-bavendorf.de
Results & Conclusions:
As fruit ripened, the amount of light recorded from the external light source decreased dramatically and the difference in the
amount of light (area under the curves) observed from the two external light positions (P1 minus P2) reduced from ~20% to ~4% in
the week immediately before harvest. Theses changes are most likely due to increased internal scattering and could potentially be
used as a fruit ripening index when measured systematically with an improved field instrument.
Variation between individual fruit was large. Most fruit ‘glowed’ while others remained dull when lit up with the external lamp.
Some trends (differences) between morning and evening scans taken on the same day could be observed.
The influence of rainfall, carbohydrate accumulation and the diurnal fruit growth patterns on the light movement through fruit
tissue requires further investigation.
Material & Methods:
A VIS/NIR spectrometer (F-750, Felix Instruments, Camas, USA) was fitted with a movable external light source (16W halogen).
A rubber grommet allowed the end of the external light to stay in the same position on the fruit surface, but the angle of incidence
light could be changed by ~7%. In Sept. & Oct. 2017, repeated scans of 40 ripening ‘Braeburn’ apples still attached to the tree were
conducted with the sensor orifice placed at the same location on the fruit surface and the external light source able to be moved
between two external positions. Scans (3x reps) per position were taken during darkness (morning and/or night) and data from the
F-750 calibration scan (shutter open, internal lamp off) were used for analysis. Soft foam padding was fitted to the sensor orifice to
block stray external light. The mean area under the wavelength versus spectral intensity curves for the 3 repeated scans from the
two external light positions was calculated and the difference expressed as a %.
Introduction:
When light passes through fruit tissue, the spectrum observed is a result of both absorption & scattering processes. It is possible to
separate these effects with laboratory methods. The reducing scattering coefficient can potentially provide information about tissue
structure. As apples ripen on the tree, the tissues change dynamically on a daily basis, as cells grow and the intercellular space
increases. The intercellular space and the apoplast (the space between cell membrane // cell wall) are either filled with fluid or air.
Fruit
that
glow
Fruit
that
remain
dull
Acknowledgements
Ryan Lerud, formerly with Felix Instruments, for advice on the F-750 settings.
Josef Streif, KOB Bavendorf, for help to construct the external lamp.
Pol Tijskens, Wageningen University, for encouragement with ‘R’.
~7° angle diff.
between
P1 - P2
Competence Centre for
Fruit Production Lake
Constance Germany
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