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# Histological assessment of fruit skin thickness on four Apple cultivars

François Laurens, Benjamin Moutault, Michel Chevalier

► To cite this version:

Francois Laurens, Benjamin Moutault, Michel Chevalier. Histological assessment of fruit skin thickness on four Apple cultivars. 5. International Postharvest Symposium, Jun 2004, Vérona, Italy. International Society for Horticultural Science, Acta Horticulturae, 682, pp.2238, 2005, Acta Horticulturae. hal-01605502

HAL Id: hal-01605502

https://hal.science/hal-01605502

Submitted on 4 Jun 2020

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# Histological Assessment of Fruit Skin Thickness on Four Apple Cultivars

F. Laurens, B. Moutault, M. Chevalier

Centre INRA d'Angers UMR GenHort - INRA/INH/UA BP 60057 - 49071 Beaucouzé CEDEX - France

Skin thickness can dramatically depreciate the taste of apple fruit. This research was performed in the frame of a regional project focused on apple texture analysis based on instrumental, histological and sensory approaches. The present study aims to automate the characterization of the sub-cuticular cell layers in order to assess relevant morphological features with the current software and tools available in our lab: size, shape and cell wall thickness.

## Material and Methods

Four apple cultivars were studied: 'Ariane', 'Verline' (both newly released scab resistant cultivars), 'Pink Lady' and 'Granny Smith'. They were selected in previous sensory tests for their contrasting skin thickness. Skin samples were collected on both the blush and non-blushed sides at the equatorial part of the fruit. They were fixed and embedded as described by Chevalier and Lespinasse (1994). Semi-thin sections

were cut at 4 µm with a Leica RM 2165 microtome, stained by Periodic Acid Schiff coloration (PAS) and mounted in synthetic resin. Images were acquired using a BH2 Olympus microscope by a triCCD SONY camera and a CG-7RGB acquisition card. The image analyses were performed with the SCION image programme.
In this preliminary study, only one fruit/cultivar was sampled; 30 images were acquired for each fruit side.

The protocol for skin thickness assessment was as follows:

<figure><img src="image_3.png" /><figcaption>Fig. 1a: Selection of a sub-cuticular zone on a section stained by PAS coloration - cvar 'Verline'</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>Fig. 2a: Cell identification after making binary the selection - cvar 'Verline'</figcaption></figure>

1

Delimitation of the studied zone: 3-4 cell layers under the epidermis (Fig.1a and b)

2

The selection is made binary (black and white) (Fig.2a and b)

3

Using the SCION image software the number of cells and some morphological parameters are computed for each cell: surface, length and width.
The percentage of wall surface is then estimated, expressed as the % of white pixels in the selected area.

<figure><img src="image_5.png" /><figcaption>Fig. 1b: Selection of a sub-cuticular zone on a section stained by PAS coloration - cvar 'Granny Smith'</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>Fig. 2b: Cell identification after making binary the selection - cvar 'Granny Smith'</figcaption></figure>

## Results - Discussion

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There was a significant effect of the factor 'variety' on the two studied variables (% of cell wall, cell density; Fig.3 and 4; ANOVA results not presented here). The amount of cell wall also showed a significant 'fruit side' effect (Fig.3), which was much larger on the two bicoloured cultivars 'Ariane' and 'Pink Lady' compared to the two green skinned cultivars. The fruit of 'Granny Smith' showed histological features with a lower amount of cell wall and a higher number of cells compared to the other three cultivars.

We have shown the efficiency of the method, which allows to acquire and analyse 30 sections in less than one hour, and to characterize accurately different histological features from different cultivars. Further studies are planned now to correlate histological observations with data from instrumental tests (penetrometer, compression, ...) and sensory analysis.

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INRA