Non-invasive russet detection on apple and pear fruit

1) Background: Russet is a brown necrotic appearance or physiological disorder of pome fruit. 2) Objective: The objective of the present work was to identify russet in-situ on the fruit epidermis using new non-invasive technology with real-time data processing. 3) Materials and methods: Colourimetry, spectrometry, 3D profilometry and a luster sensor, were employed on ‘Conférence’ and ‘Williams Christ’ pear cultivars. 4) Results: Non-invasive true and false colour images at 40× magnification with a 3D-profilometer type VR-3000 (Keyence) allowed identification of russet on ‘Conférence’ pear with arithmetic roughness (Ra) larger than Ra 3.3 µm (SE 0.4) compared with Ra 2.5 µm (SE 0.3) on russet-devoid fruit epidermis.
The non-invasive russet detection using the luster sensor CZ-H72 failed to detect a significant difference (8 a.u.) in glossiness between russet (54.5 a.u.) and non-russet (62.5 a.u.) on ‘Conférence’ (green) in contrast to red ‘Williams Christ’ with nearly a 2-fold statistically significant difference between russet (38.4 a.u) and non-russet (67.5 a.u.) surfaces.
The situation reversed with colourimetry: For the red pears ‘Williams Christ’, differentiation between a russet (66.8 °hue) and russet-devoid epidermis (62.4 °hue) was impossible when using non-invasive colourimetry.
For green pears, however, a statistically significant difference in colour angle could be detected between russet (79.9 °hue) and russet-devoid (94.8 °hue for ‘Conférence’) fruit.
Russet could be successfully detected for all cultivars using portable non-invasive spectrometry (500-1100 nm). A new spectral russet index was proposed relating the two peaks of light reflection (550-600 nm and 775-785 nm) to the nadir (667-685 nm). Russeted epidermis (e.g. 3.6) exhibited 20-25% smaller SRI values than russet-devoid epidermis (4.2 and 4.8) of ‘Conférence’ (green) and ‘Williams Christ’ (red) cultivars, irrespective of epidermis colour. 5) Conclusions and outlook: Overall, both non-invasive techniques, 3D-profilometer and spectral light reflection with the novel russet index, proved suitable for russet detection in pears.
In particular, the study has identified colourimetry as a suitable measure for russet detection for green and a luster sensor for red pear cultivars.
The study has also shown that russet can be identified non-invasively by a range of new affordable mostly portable technologies in real time, which offer new possibilities of russet detection in the orchard or on a grading line.

IV International Symposium on Horticulture in Europe – SHE2021

M. Schuesseler, L. Damerow, M. Blanke

pear Pyrus communis L., consumer appeal, fruit epidermis, fruit quality, glossiness, non- invasive detection, epidermis roughness, postharvest, red pear, russet, surface roughness, yeast

https://doi.org/10.17660/ActaHortic.2021.1327.89