In this interview with Dr. Bouvet, whose main role in AHDB is helping to disseminate the learnings from storage research to potato growers, storers and processors, she talks about what potato storage operators can do to prevent or get rid of some of the most common diseases.

What are the most common food safety threats that occur in stored potatoes?

There is this misconception of potatoes as being something inert once they’re in storage. But potatoes are alive and their physiology continues to change in storage. As they age, starches break down into sugars, which can lead to issues that reduce the value of the product. Tubers remain dormant initially but will eventually break from this dormancy period, leading to sprouting if left untreated. This can also reduce the value of the product.

There are three main diseases and physiological issues which I tell potato storers and processors to be wary of, these are:

• Rots and blemish diseases
• Sugar buildup
• Sprouting

The impact of these issues further down the distribution chain depends largely on whether the potatoes are destined for fresh pack sale, processing or for animal feed.

The fresh-pack sector demands low levels of blemish diseases – these diseases cause visual abnormalities which reduce the value of the potato to consumers. An example is black dot – which shows up as light to dark brown patches with black dots on the skin surface, detrimental from a visual perspective.

For processors, those sugar levels are important. High sugar levels can lead to unacceptable fry color, affecting quality further down the supply chain in a number of ways. Dark crisps or chips can indicate the presence of unacceptable levels acrylamide, a known probable carcinogen. There are commercial standards from a food safety perspective to keep acrylamide levels as low as possible, and that means keeping an eye on their fry color in storage with fry color tests. (Acrylamide is a biproduct of the cooking of starch products at high temperature – it’s the asparagine glycoprotein in the starch that causes it, and that asparagine builds up as the potato starch breaks down).

Sprouting in storage is one of the main concerns for store managers, particularly now that chlorpropham (CIPC) has been withdrawn and available alternatives aren’t like-for-like replacements. It affects the downstream value of the potato – whether that’s in processing where sprouts need to be removed prior to processing, or the fresh pack sector – because visually they affect consumer demand. Left untreated, sprout growth will cause water and weight loss as the potato respires and grows, reducing weight-at-sale by 2-3%, so it’s important to keep sprout growth under control during storage.

How much do diseased potatoes impact the distribution chain?

While few diseases actually originate in stores, it’s really important to keep an eye on and control diseases such as blemish diseases and also soft rots. Processors and packers work according to a set of specifications that growers and storage managers need to comply with, and there is a certain percentage level of disease that is commercially acceptable – so disease management is important to meet those specs and minimize waste.

What are the current best means of preventing and removing sources of infection and contamination in potato storage units?

Sniffing your store is still one of the best ways to monitor diseases, particularly for soft rot. And for blemish diseases, using the eyes. There’s no specific sensor for monitoring diseases in store yet – although B-Hive in the UK are working on developing such a thing, and have been given a government grant to help bring that to market. But as it stands, it’s still more prevalent to use the nose when carrying out regular store checks. Prevention is better than cure and the way you would prevent disease or reduce disease is by thorough cleaning once the store is empty, particularly if rots have existed previously and inoculum may be present – so it is about giving a deep clean, removing as much debris and residue as possible – in order to allow no breeding ground for spores to germinate. And then most diseases come from the field or the seed, so it needs to be a joined-up process of prevention in the field coupled with prevention in storage. I’ve started to encourage growers and store managers to think more about Integrated Store Management (ISM) – a multidisciplinary approach to storage – thinking about the storage environment and its management, the use of physical, biological and chemical measures for controlling disease pressure and sprouting, considering varietal traits – so integrating all of these different components as a whole, is crucial for storage moving forward. When it comes to loading the store, disease grading is important to make sure diseased potatoes aren’t stored with healthy potatoes – that’s all part of ISM – to keep disease levels down. It is difficult to treat pathogens that are attacking potatoes once they’ve spread in storage, hence why prevention and monitoring are important. Regular monitoring lets you make sure that disease levels stay down. One way is to divide up the store space so that if one sector develops a problem, it can be separated from the rest of the store to prevent spread.

How do you believe 2021 will impact the potato business?

The potato sector particularly processing has been hit really badly as a result of the pandemic and in particular as a result of the closure of the foodservice sector pretty much overnight when the country first went into lockdown last year. As a result, the supply and demand dynamic has completely shifted, which means that processors still have stock stored from last year. Now that we’re onto a new production year, what happens to the new stock? With the restaurants still closed at the moment demand has struggled to pick up again. There has been an uplift in demand from supermarkets as more people are cooking at home, but this hasn’t compensated entirely from the limited capacity of the foodservice market. So, I would expect the situation to improve in 2021 as the vaccine is rolled out and we get out of lockdown, potentially things will ease up, but there will be this lag as stored product remains to be used.