Caractérisation de la qualité culinaire et technologique des pommes de terre de consommation

Characterization of the culinary and technological quality of consumption potatoes

Context

For 45 years the Farming Systems Section of the walloon agricultural Research Centre (CRA-W) has been active in research on the different aspects of the potato production.

Among the whole of its research activities, the Section developed a considerable experience in the field of the productions qualification.

The developed expertise permits to determine the following parameters: weight under water (dry matter), quantification of the external and internal defects, technological quality (frying colour index, after-cooking blackening), or culinary quality (flesh consistency, colour, humidity, appearance on the dish, taste intensity, flouriness, etc.). The figure 1 illustrates the number of analysis carried out at the Farming System Section during 2003/2004, as well as its distribution between the different qualitative criteria.

These analysis are carried out in routine by the Quality Potato laboratory at the request of various types of clients whose needs are variable :

we are in charge of analysis for inscription,of new potato varieties to the national list;
farmers ask for rapid and reliable analysis of the dry matter content, in order to control at best the orientation and the price of their productions;
we call upon the tasting jury for the Section’s breeding program;
the organism Procerviq, in order to look after the respect of culinary aspects according to the reference lasting book of Terra Nostra trademark;
the organism Promag asl for analysis in the frame of its works on the Platte de Florenville variety;
and the BPQA (Best Potato Quality Award) jury, which rewards the potato grower who succeeds in the production of high quality potatoes in the respect of good agricultural practices.

However the determination of certain parameters is done by visual estimation (with reference pictures, colour cards) or sense of taste. Therefore, although carried out by a coached staff, it remains a part of subjectivity that physical analysis techniques could reduce at least.

Objectives

Among the parameters determined at the laboratory appear the frying colour index and the after-cooking blackening.

The quality of potatoes intended for frying (fritability) is defined by three criteria :

The frying colour index : it represents the colour of a french fries batch, it is determined by visual comparison with a reference card, by ranking 20 french fries among 7 colour categories going from 000 (no blackening at all) to 00, 0, 1, 2, 3, and 4 (french fries totally tanned), and by calculating a weighted average;
The number of colour categories (maximum 7) : it reveals the homogeneity of the batch;
The number of brown bits (darker colour at the French fries ends).

The programming of an image analysis software for the determination of these three criteria would make it possible to replace the quotation of judges by digital vision, more objective and reliable.

Expected results

Validation of the method and transfer to laboratory of the FIWAP, in Gembloux.

Results obtained

The determination of the three parameters relative to fritability with the image analysis is almost finalized. Indeed the programming and the calibration are finished.The calibration gives very good results (R² = 0.9040 between the reference analysis and the new technique) compared with the weak repetability of the reference method submitted to the judgment of colours by human eye.The advantages of this technique are multiple : once the software is finalized, its use is easy, what reduces needs in qualified staff; results are reliable and easily archived (storage of the pictures taken by the software for the image analysis; automatic emission of a report); the method is rapid.The prospects of improvement of the technique are at two levels. On the one hand, the size of the trays used to arrange the 20 analysed french fries aren’t adapted. Indeed they are sometimes too small in comparison with the size of the marketed french friesand it is essential that french fries don’t adjoin at the time of the picture taking.

On the other hand the necessity to distinguish 7 colour categories must be revised because the clear references (000 and 00) are hardly discernible.

Contribution

The Farming Systems Section is the project leader. It is occupied of the establishment and the follow-up of the project, as of the analysis of the results.