Chlorpropham (CIPC), the main sprout suppressant used when storing commercial potatoes, is now prohibited in Switzerland. Agroscope tested alternative substances in order to guarantee the production of indigenous chips and crisps.
Chlorpropham (CIPC) is a highly effective compound that has been used throughout the world for decades to control potato sprouting over several months of storage. Following a re-evaluation of the approval file of this product and owing to its unfavourable toxicological profile, CIPC is no longer approved in the European Union as of January 2020.
In Switzerland, the sale of CIPC has been banned since 15 August 2020, and the use-up date for existing stocks was 30 September 2020. This means that Switzerland could still treat potatoes with CIPC when they went into storage in 2020, provided that these treatments were carried out within the legal deadlines. However, treating potatoes with CIPC in 2020 was discouraged, in order to avoid problems of residues in the tubers and storage cells, given the high persistence of this compound in storage facilities.
Six alternative compounds studied
Anticipating this situation, Agroscope, together with different partners*, conducted a series of trials from 2015 to 2020. The aim was to find alternatives to CIPC in order to continue to maintain the quality of the potatoes intended for commercial use (chips and crisps) over the storage period. The researchers studied the efficacy of six compounds as sprout suppressants: L-carvone (contained in mint essential oil), limonene (contained in orange essential oil), 1,4-dimethylnaphthalene (1,4-DMN), 3-decen-2-one, maleic hydrazide and ethylene. Ethylene, which can increase the level of reducing sugars** (which are undesirable in potatoes) in certain varieties, has also been tested in combination with 1-methylcyclopropene (1-MCP). The use of 1-MCP limits the risk of developing reducing sugars, which can cause undesirable browning and the production of toxic acrylamide in processed products.
All of the compounds tested proved effective in controlling tuber sprouting, with varying levels of efficacy. Despite this, none of the compounds compared with CIPC was as effective, and their use was for the most part more restrictive and/or more expensive. Three of these compounds are already authorised in Switzerland: ethylene, L-carvone and maleic hydrazide, each with their constraints. 1,4-DMN, on which the hopes of the sector are pinned and which is already approved for use in numerous countries, has just been authorised in Switzerland.
Researchers face a challenge on multiple fronts, since the aim is to maintain high-quality, sprout-free tuber stocks, without toxic residues and without an increase in reducing sugars, all over a period of several months.
*Partners: Swiss project partners: Fenaco, Zweifel, Innosuisse – the Swiss Innovation Agency, and Swisspatat. Belgian project partners: UPL Benelux, the Walloon Region (subsidised by EUREKA) and the Gembloux Agro-Bio Tech University of Liège.
**Reducing sugars: High amounts of reducing sugars in potatoes are to be avoided for commercial varieties, as they can cause a bad (sweet) taste, the browning of processed products when fried (chips and crisps) and the production of toxic compounds such as acrylamide in processed products.
***Sweetening: Sweetening in potatoes is caused by an increase in reducing sugars in the tubers. This undesirable phenomenon can happen with certain varieties when stored at low temperatures, but also during the physiological ageing of the tubers over time.
In order to be effective, alternative compounds to CIPC will have to be combined with new storage strategies. Agroscope researchers are working on different innovative solutions for controlling sprouting:
- A sprouting model was developed to predict the sprouting date of a given variety based on weather parameters. In particular, this model will help to reduce or avoid the application of products.
- Identification of commercial varieties not susceptible to sweetening*** when stored at low temperatures (4 °C or 6 °C), which would allow tuber sprouting to be delayed. Three varieties have already been identified: Lady Claire, Verdi and Kiebitz.
- Reconditioning: This technique consists in storing varieties prone to sweetening at a low temperature (4 °C), followed by a reconditioning period (gradual raising of the temperature up to 15 °C). Reconditioning enables a significant reduction of reducing-sugar levels in certain susceptible varieties.