Research Results

Kiwi - NIR measured on skin or flesh

In GreenCHAINge fruit & vegetables, non-destructive measurement techniques are explored and developed. The general aim is to measure quality aspects non-destructively, objectively, repeatable and reliably. One of those measurement methods is by using NIR. In this subproject, NIR measurements of kiwi are explored.

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To measure the quality of kiwifruit with near-infrared spectroscopy (NIR), it is important to know if the NIR measurement can be done on the skin of the kiwi or if the flesh needs to be visible before a proper measurement can be done.

Experiment and Results

More than 350 kiwifruits were stored at 20 °C. The kiwis were measured using a SCIO portable NIR (reflectance mode) spectrometer. Each kiwi was measured with and without skin. Firmness, determined with a penetrometer, and Brix measurements were taken as reference (ground truth).

Correlation matrix of NIR measurement with Brix and Firmness measurements

R2 measured on Flesh R2 measured on Skin
Brix 0.745 ± 0.036 0.564 ± 0.055
Firmness 0.553 ± 0.054 0.440 ± 0.053

The prediction (R2) of the Brix and Firmness was improved by removal of the skin. The skin of kiwi suppresses reliable non-destructive measurements of internal quality characteristics like Brix and firmness.


The SCIO portable NIR can better predict firmness and brix based on measurements on the flesh than measurements on the skin.