Context
At the present time none recent study was carried out on the food safety of - consumption potato. But, because of the harmful effects of previous alimentary crisis in Belgium, it is proved to be judicious to carry out an inventory of fixtures as for the presence of pollutants from various origin in potatoes; in particular heavy metals, nitrates, residues of pesticides and solanin and chaconin. These two glykoalkaloïds are naturally present at low rates in tubers, but their production may be stimulated by some factors and reach dangerous concentrations for human health.
Moreover the determination of the potato quality standards needs the use of various analysis methods, which have as main characteristics rapidity and reliability. At present, several proximity laboratories exist in Wallonia, where growers may ask an estimate of their batches in order to optimize their valorization. Unfortunately these laboratories have developed their own personal analysis protocols. Therefore to answer to the needs of the profession, the development and the harmonization of analysis methods proved to be necessary in order to confirm the credibility and the reliability of the analysis carried out in the different proximity laboratories.
Objectives
On the one hand the project aims to carry out an inventory of fixtures about the presence of pollutants (heavy metals, residues of pesticides, nitrates and glykoalcaloïds contents) in the consumption potatoes in Walloonia.
On the other hand the project aims to seek and develop new analysis techniques for potato quality standards.
Lastly a field is devoted to actions of information, advice and technical support for the professionals working in the potato field in order to guide the techniques of production toward the respect of the quality parameters.
Expected results
-) Inventory about the presence of pollutants :
We noticed an overspending of the norm for some heavy metals however the way we took the samples doesn’t allow us to determine the origin of the overspending. Studying this complex problem goes beyond the scope of this project and should include the identification of all the factors influencing the potatoes heavy metal content.
Content in nitrates, glycoalcaloïds and residues of pesticides (13 different active substances) are under the MRLs; except for a series of sample that shows a cholpropham content superior to the MRL that is explained by the period of sampling, realised just after the application of the sprout inhibitor.
-) Development of new analysis techniques :
NIRS : In comparison to the average results obtained, we decided to stop the trials. Indeed we aimed to find a more operational approach for this project applicable to entire tubers within the process chain. But previously studied approaches on crushed and freeze-dried potato samples gave better performances, but the samples conditioning was long and boring what removes all its interest to the technique.
Image analysis : firstly this technique was developed for the determination of the frying colour index although it still must be validated by repetability and reproductibility trials. Secondly it is in development to determine the after cooking blackening because the estimation is currently made by visual comparison with reference cards.
Results obtained
Development of new analysis techniques :
- Near Infra Red Spectrometry (NIRS): this method is developed in order to specify the potato composition and organoleptic or technological characteristics in a rapid and standardized way. At the beginning, NIRS was tested on entire tubers, no peeled, with a view to develop a method as rapid as possible. Unfortunately, the method didn’t give satisfactory results: the coefficient of determination is under 50 % for the culinary type prediction. It is superior to 60 % for all the biochemical parameters, and it exceeds 70 % for the dry matter, after cooking blackening and sugars content. However even for these latter parameters, calibrations are short of precision and don’t allow any quantitative amount.
- Image analysis : this method is used for the determination of the frying colour index. This one reveals the colour of a batch of french fries, an essential standard for the varieties marketing (For more information about this method, see the page relating to the project “Characterization of the culinary and technological quality of consumption potatoes” on this website). At the present time, the index is determined by visual comparison with reference cards, in other words, according to the judgment of colours by human eye, including a part of subjectivity. The use of an image analysis software makes the method more objective. That’s why the programming and the calibration of the software were developed. The coefficient of determination is up to 0.9040 between the reference analysis and the new technique, it is a very good result compared with the weak repetability of the reference method, submitted to the judgment of colours by human eye.
- Card of determination of internal defects : by the calculation of an index this card makes it possible to assess the extent of internal defects of a potato batch. Defects are estimated by comparison with a reference card presenting 18 pictures of potatoes damaged at increasing levels. The percentage of defects compared with total surface area of the tuber was calculated by image analysis. Defects were then divided into 5 categories of increasing gravity, which correspond to a coefficient allowing the calculation of the internal defects index. This card is currently used as part of Terra Nostra trademark analysis.
Contribution
Department Pesticide research: determination of residues of pesticides in potatoes.
Department Crop production: determination of nitrates content in – potatoes.
Department Quality of agricultural products: determination of heavy metals content in potatoes, development of the NIRS.
Farming Systems Section: determination of solanin and chaconin contents in potatoes, development of the image analysis software and the card for the determination of internal defects, coordination of the project.
Partners
Ministry of the walloon Region;
Asbl FIWAP;
Asbl REQUASUD.
CRAW off coordinator
SOETE Alice (Attachée scientifique)
Section Systèmes agricoles
Rue de Serpont, 100
B-6800 Libramont
Tél. :+ 32 (0) 61 / 23.10.10
Fax :+ 32 (0) 61 / 23.10.28
E-mail :soete@cra.wallonie.be
Funding
- DGARNE
