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Ageing in store

1 May 2012

If you are storing potatoes until this time of year, tuber ageing is going to affect your crop and probably in more ways than one. How?

The simplest effect is through potatoes losing moisture. Weight loss results in softening and shrinkage, maybe even compression damage. Dehydration is a fairly simple, physical process and we understand what we have to do to limit it - keep humidity high and fan hours low. But, at the same time, crops are ageing physiologically. These processes are not very well understood but can have further, serious consequences for crop quality and saleability.

Store managers and processors of potatoes recognise senescent sweetening - an irreversible increase in sugar content that marks the end of useful storage for processing. Varieties differ in the timing of the onset of senescent sweetening and this is also influenced by storage temperature. While the exact mechanism is not known, variety characteristics are sufficiently well understood  for purchasers to draw up fairly sophisticated processing timelines, especially in the crisping sector where sugar content (and therefore fry colour) is of critical importance. It is their susceptibility to senescent sweetening that gives us the progression of varieties used for processing. So, often, whilst Lady Rosetta would be used initially, this gives way to Hermes for the medium storage durations and then, finally, Saturna - which is relatively resistant to senescent sweetening - for long-term storage.

Blackheart is another defect associated with tuber ageing.  It is thought that blackheart does not normally occur in the field, and only manifests itself after storage, with risk increasing as storage progresses. It is a physiological disorder resulting in blackening or necrosis, and sometimes cavity formation, in the centre of a tuber (see photo). It can be influenced by the availability of oxygen within the central tissues but this is not always the case. From the outside, tubers usually appear sound so the blackheart cannot be detected - and therein lies the problem.

More recently, blackheart has emerged as an increasingly frequent problem for the GB packing industry. SBCSR, working in collaboration with Cranfield University and the Fresh Potato Suppliers’ Association, is currently researching risk factors and potential mechanisms leading to blackheart formation. The team at SBCSR would like to hear from store managers who believe they may have crops with symptoms similar to those shown in the photo. Please phone 0800 0282111 or email adrian.briddon@ahdb.org.uk if you can help.

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