Potato storage: quality management

With the highest level of potato consumption in the world, Europe needs to store large quantities of the potato crop, sometimes for long periods, both for the processing industry and the fresh trade.

With the highest level of potato consumption in the world, Europe needs to store large quantities of the potato crop, sometimes for long periods, both for the processing industry and the fresh trade. Maintaining quality during storage is of prime importance and Good Agricultural Practice allows the controlled use of approved crop protection products to assist in both production and storage of a healthy, quality crop. As a result of the mode of action of some of these products there may be instances where product residues in the crop, substantially below the officially recognised Maximum Residue Levels, cannot be avoided and must be balanced against the resulting quality of the product which could not otherwise be maintained.

The potato processing industry requires a year round supply of raw materials and imposes strict quality standards on growers and suppliers. Major concerns relate to skin quality, which can be damaged by disease, and secondary growth or sprouting, which is undesirable as it causes weight loss, quality deterioration and subsequent wastage.

Disease protection starts with seed treatments applied to protect tubers in storage against a variety of fungal diseases such as Fusarium spp., Phoma spp., Helminthosporium solani, which would damage their quality as seed potatoes. Pre-plant treatment against Rhizoctonia is used effectively to reduce disease pressure on the crop in the ground and is therefore a key tool in Integrated Pest Management systems. Without their use increased treatment levels would be required during the crop season.

Potatoes used for processing pose considerable challenges in that storage at temperatures sufficiently low to maintain dormancy causes the formation of higher sugars in the tubers. These lead to browning of the potato and to an increase in the levels of acrylamides formed during processing, from the interaction of the sugars with amino acids naturally present. To avoid the higher sugar levels potatoes for processing are therefore typically stored at 7-9°C. Discoloration from high sugar levels is even more important in potatoes for crisp production so these are stored at 9-12°C to help keep sugar levels down. At these temperatures, sprouting will also cause irregular sugar concentrations in the tubers, resulting in irregular fry colours. Effective sprout suppression is therefore vital.

However, in terms of sprout suppression, the processing industry has a very limited range of options. Growth regulator, maleic hydrazide, may be used in the field pre-harvest and Chlorpropham (CIPC) in store. The former will prevent sprouting for a few weeks after harvest and may save one treatment of CIPC in store. It also offers the benefit of reducing the occurrence of volunteer potatoes, which can be a weed in a following crop, and the source of potato blight infection as well as a cause of build up of nematode problems and soil-borne diseases. If maleic hydrazide is not used, potatoes for processing will need to be treated to prevent sprouting if they are to be stored for longer than 2 or 3 months. This can be done as they are placed in store with CIPC applied as a liquid (Gro-Stop Ready, Gro-Stop Basis ) or as a fogging treatment when the stores have been filled, but preferably within 3 weeks after store closure (Gro-Stop Fog, Gro-Stop Innovator, Gro-Stop Solid). Frequent checks must be made on the need for a further sprout suppressant application.

Both maleic hydrazide and CIPC are known to leave some residues in the tubers or in the skins but, with no viable alternative to CIPC, and sprouting rendering the crop useless for processing, these must be balanced against the requirement for high quality crop specifications and management in the storage process to achieve those. Suppliers, growers and processors are working to manage the use of the actives, with low dose rates and innovative techniques in order to keep residues to a minimum. The residues that do occur are well below permitted Maximum Residue Levels (MRLs) and are present as part of a managed programme to provide control and maintain the quality of the crop for processing.

Mark Verhooren, manager of LambWeston Meijer, a major European processor, confirms that the quality of the raw material is vital to the production of good quality processed products and that they are trying to protect the products currently used to provide that security by careful stewardship:

"We are working closely with our growers and crop protection solution providers, Certis Europe, to develop innovative and sustainable stewardship programmes to provide high quality stored potatoes for the processing industry. The residues seen in these potatoes are very small and far below the maximum acceptable residue levels prescribed by the authorities. Without CIPC we would not be able to maintain the required quality standards of the crop for successful processing."  

Potatoes for fresh consumption are normally stored at the lower temperature of 2-4°C to help maintain the quality and dormancy of the tubers. In some circumstances ethylene used at very low concentrations can successfully maintain dormancy but sometimes, particularly if stored for long periods and depending on the variety in question, there may still be a need to use CIPC to prevent sprouting. As a result residues may also be found in some fresh potatoes but this must be weighed against the fact that sprouting potatoes are unacceptable to consumers since they quickly become unusable.

It is important for processors and users of fresh potatoes to have a supply of high quality, disease free potatoes through the year, matching their quality requirements. Careful management of the stored crop and sound stewardship of the crop protection products available is vital to providing that.

Notes

Production of potatoes has declined in Europe by almost a quarter in the last 10 years from 80 million to about 61 million tonnes and, whilst the continent still has the highest level of potato consumption in the world, more of the production is now processed by a sophisticated industry, providing substantial exports. Processing is concentrated in UK, Netherlands, Belgium, France and Germany, where production has remained more or less flat. The EU-27 Potato Products Annual (USDA) (22.12 2009) reports that the processing capacity in North-Western Europe grew over the past decade grew from 11 to 14 million tonnes of potatoes per year, and expectations are that this trend will continue.

For more information please contact:

Kevin Price Market Development Manager Certis Europe T: +32 2 331 3894 E: price@certiseurope.co.uk

Gill Norriss Corporate PR Sequitur T: +44 1794 388 831 E: gillnorriss@sequitur.eu.com

About the Company

Certis Europe includes operating units in France, Netherlands, Belgium, Italy, Spain and UK, as well as BCP Certis. It also has close links with Certis USA and Spiess-Urania.

Mitsui & Co. markets and distributes a wide variety of pesticides, bio pesticides and biological pest control products and services through its European, Japanese, African and U.S. marketing subsidiaries. 

Useful Certis group & Mitsui & Co websites:
Certis Europe: www.certiseurope.com
BCP Certis: www.bcpcertis.com
Certis USA: www.certisusa.com
Mitsui & Co: www.mitsui.co.jp