Put the safety of nuts first: dried fruits and well-being

14 November 2018

Low-moisture products, such as nuts, dried fruits and spices, are often thought of as ‘safe’; however, following a number of product recalls, we are seeing a heightened focus on their microbiological quality. Ingredients Insight takes a look at how safe these products are and sees whether innovative pasteurisation services can be used to treat them.

Low-moisture foods, like dried fruits and nuts, are not usually seen as potential culprits for food-borne illness. We know such products can cause allergic reactions in those susceptible. But unlike, say, sour milk or raw eggs, they do not famously fall foul of dangerous microbes.

True enough, dried food products are not the riskiest category on the market. The European Food Safety Authority (EFSA), which is the EU risk assessor for food and animal feed, does not consider them a major concern – at least not compared to other products.

“EFSA has not worked specifically on an assessment of the microbiological risks posed by dried foods,” explains Pietro Stella, scientific officer at EFSA’s Biological Hazards and Contaminants Unit. “In 2013, EFSA published an opinion that aimed to identify and rank specific food/ pathogen combinations most often linked to food-borne human cases originating from food of non-animal origin in the EU. No dried food of nonanimal origin was included among the five top ranking groups of food/ pathogen combinations.”

The list, however, does include several products that are naturally low in moisture. Specifically, it mentions spices and powdered herbs that are contaminated by Bacillus or Salmonella, as well as nuts and nut products contaminated with the latter. “Food safety risks in minimally processed dry products like almonds, pistachios and peanuts are different from high-moisture foods,” reads part one of ‘Risk posed by pathogens in food of non-animal origin’.

“Therefore, the most likely sources of contamination by food-borne pathogens are animal wastes, particularly manures that have been added to improve soil texture and as a fertiliser.”

The report adds that, as a result of hygiene conditions in the growing regions, spices are particularly susceptible to microbial contamination from food-borne pathogens. In 2007– 11, there were seven Bacillus outbreaks in the EU associated with spices and dried herbs. More than 300 people were affected, although none of these cases resulted in hospitalisation.

Beyond this particular report, stories about contaminated nuts are not hard to find. Over the past few years, Europe has seen a number of product recalls relating to products like chocolate and tahini, after Salmonella was found in certain batches. Most recently, Tesco Ireland recalled a batch of organic almonds.

The health and well-being of almond consumers matters deeply to everyone in the California almond industry. We’re not afraid to tackle food safety challenges head-on.
– Tim Birmingham, Almond Board of California

Across the pond

The same applies across the Atlantic. In 2015, the grocery store chain Kroger recalled some of its popular spices due to a possible Salmonella contamination, while Whole Foods recalled its packaged raw macadamia nuts the following year. In 2018, Kellogg Company recalled 1.1 million packets of Honey Smacks cereal after preliminary evidence linked the product to more than 60 cases of Salmonella.

Perhaps the biggest cautionary tale, however, is that of the disgraced ‘peanut executive’ Stewart Parnell, who in 2015 was sentenced to 28 years in prison for his role in a 2008–09 Salmonella outbreak. Parnell, the former head of the Peanut Corporation of America, was found to have knowingly provided Salmonella-tainted peanut butter to its customers, leading to one of the largest food recalls in US history.

It is clear, then, that nuts, spices, seeds and so forth are not inherently ‘safe’. In fact, they carry microbiological risks that need to be addressed appropriately, often by means of pasteurisation.

“In the previously mentioned 2013 EFSA opinion on the food of non-animal origin, some aspects of pasteurisation are discussed in relation to dried fruits and vegetables, fruit and vegetable juices, and heat-treated products,” adds Stella. “For dried fruits and vegetables, it is mentioned that, in some cases, pasteurisation or the addition of preservative such as potassium sorbate is needed.”

In fact, the pasteurisation of nuts has been a hot topic in the ingredients industry since 2007, when the US introduced mandatory pasteurisation laws, which pertained to almonds. These came about as a result of serious Salmonella outbreaks in 2001 and again in 2004. At the time, low-moisture products were considered a minimal threat, but the Almond Board of California (ABC) investigated further and discovered Salmonella could pose a problem.

California, which produces nearly 80% of the world’s almonds and close to 100% of the domestic supply, has long set the tone for the industry. ABC’s research, conducted over a period of several years, found that around 1% of the almonds tested did contain low concentrations of Salmonella. This spurred the board to establish standards for the market. Since then, there have been no further outbreaks associated with California almonds.

“The health and well-being of almond consumers matters deeply to everyone in the California almond industry. We’re not afraid to tackle food safety challenges head-on, aided by the expertise of our partners, and we’re proud of our pioneering best practices,” said Tim Birmingham, director of quality assurance and industry services at ABC, in a release. “In response to concerns about Salmonella, we conducted research and led extensive discussions with industry, university and government experts before adopting mandatory pasteurisation. After ten years with zero outbreaks, we are grateful that we took action.”

To date, ABC has invested a further $5 million in food quality and safety research, and has validated more than 200 treatment processes. One such treatment is steam processing, in which a short burst of heated steam treats nuts. The advantage here is that they can still be marketed as organic.

Residual effects of treatment

Another, more controversial, treatment is fumigation with propylene oxide. Although this preserves nuts’ desirable characteristics, the chemical is listed by the US Environmental Protection Agency as a potential carcinogen. It has fuelled concerns about effects from exposure to the chemical residue.

What all pasteurisation treatments have in common is that they kill any lurking microorganisms. While lowmoisture foods don’t have sufficient water activity to support microbial growth, low levels of bacteria can be enough to cause illness.

What is more, the Salmonella bacteria is able to survive in nuts for long periods of time. One 2011 study found that, contrary to consumers’ belief that freezing and refrigeration kills it, cold storage actually extends its survival. The Salmonella population tested did not decline over 1.5 years of refrigeration or frozen storage. It is therefore critical to find ways to remove these pathogens – particularly since the requirements around food safety are being tightened.

In 2011, President Obama signed the Food Safety Modernization Act (FSMA) into law, which authorised the US FDA to regulate the way foods are grown, harvested and processed.

The almond industry was uniquely well positioned to comply with these requirements. Other sectors have has a much trickier task. At present, almonds are the only nut with a mandatory pasteurisation programme and defined performance criteria. Since what works for almonds may not work for pecans, for example, specific research is needed on each type of tree nut.

FDA is taking this issue seriously. On its website, the agency has stated that it will conduct “quantitative microbial risk assessments to estimate the risk of human salmonellosis arising from the consumption of almonds, pecans, pistachios and walnuts in the United States”. Industry groups, meanwhile, are conducting their own assessments.

What we do know is that contamination is reasonably widespread. In a 2017 study, researchers collected 3,656 samples of six tree nuts – cashews, pecans, hazelnuts, macadamia nuts, pine nuts and walnuts. Just under 1% of the samples (32) were confirmed as containing Salmonella.

As understanding of the risks becomes more widespread, nut pasteurisation is rapidly becoming the norm – and not just in the US, but in Europe too. While EU legislation is not as strict, product contamination and food recalls can pose a big threat to a brand’s reputation. Many of the continent’s suppliers now have a dedicated pasteurised products line – and demand for these products is growing.

As Stella explains, authorities like EFSA help producers determine the risks they are facing.

“The EFSA Panel on Biological Hazards is the body in EFSA providing independent scientific advice on biological hazards in relation to food safety and food-borne diseases,” he says. “At request of the European Commission, the European Parliament, member states and EFSA itself, the panel provides advice and adopts scientific opinions in relation to the microbiological safety of food products. The advice from EFSA is used by risk managers as a basis for their decisions on the measures to be possibly taken at EU or national level.”

Today’s producers and tomorrow’s challenges

All in all, there is a greater focus on the microbiological quality of food products. We are also seeing the emergence of a burgeoning dry foods pasteurisation industry, with a variety of different services on offer. While some producers have invested in their own pasteurisation lines, many are choosing to outsource to third parties.

Typically, a pasteurisation treatment reduces the total bacterial load in a food product, decimating the population of pathogens like Salmonella. It also preserves the colour, texture, taste and nutritional properties of the nuts, meaning they can still be classed as ‘raw’.

Of course, these kinds of technologies may not be well known – mention pasteurisation to the average consumer and their mind will turn straight to dairy products. Behind the scenes, however, it’s a different story. With low-moisture food products under more scrutiny than ever, today’s producers don’t want to take any chances.

With pasteurisation, nuts can still be classed as raw foods. This method helps to reduce their bacterial load while preserving texture, colour and nutritional properties.

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