|Authors: ||A.M. Cavaco, M.D. Antunes, T. Panagopoulos, M. Rosendo, R. Pires, A. Brázio, L. Silva, A.M. Afonso, R. Guerra|
|Keywords: ||Algarve citrus, Vis/NIRS, field protocol, optimal harvest date, orchard management|
Visible/near infrared reflectance spectroscopy (Vis/NIRS) is more and more used to determine non-destructively several internal quality parameters of fruit in the packing houses.
We have recently started a project aimed at determining the optimal harvest date (OHD) of some of the most important cultivars of Algarve citrus, based not only on the legislated values for maturation index (MI) but also on other fruit quality parameters (QP). This is mandatory for a real time and extensive orchard management, as well as to optimize the postharvest conditions of the fruit, namely, by keeping its 'garden-fresh' characteristics up to the consumer.
We perform in situ Vis/NIRS measurements in citrus fruit on the tree and monitor the time evolution of the respective spectra.
The first problem encountered was the transfer of the reflectance measurement routine from the laboratory to the field.
Indeed, therein, several problems occur that are not a concern under laboratory conditions.
For example, the lifetime of the portable spectrometer battery is a major concern.
For long and/or intensive measurement sessions, one is forced to turn off the illumination for energy saving purposes.
However, turning off the illumination usually means having to wait some minutes for the lamp to stabilize again and to perform another reference spectrum.
The other problem is that for warm days and direct exposure to the sun, the light source intensity may fluctuate due to undissipated heat.
Again, this would imply frequent reference measurements, which is not convenient.
Finally, it may even be advisable to turn off the entire system, and in this case the dark measurements are a concern, since 15 min is usually the time it takes for settlement.
In this communication we present a protocol for Vis/NIRS measurements in the field that addresses all these problems.
It is based on the use of auxiliary reference samples for frequent absolute reference compensation and on two different techniques for automatic dark compensation.
The results, taken from our data, show that our protocol yields results with much lower variability, and that this difference in data variability is due to instrumental errors induced by the usual measurement method.
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