Fruit safety and local water quality: Do they mix?

South Africa is facing a dual crisis of water availability and deteriorating water quality. Should the fruit industry be taking the situation more seriously?

By Jorisna Bonthuys

Ensuring the safety of produce from farm to market has never been so critical. In the last few years, a number of outbreaks of foodborne diseases worldwide have also shown just how important food safety is in the supply chain. This is the opinion of Prof Lise Korsten from the University of Pretoria, Institute of Food Nutrition and Well-being and the Department of Science and Technology/ National Research Foundation Centre of Excellence in Food Security. Her teams’ research has over the last decade focused on developing a food safety framework for the local fruit and vegetable industries.

Korsten, considered a world leader in her field, has been closely involved in studies on irrigation water and food safety. This includes coordinating a four-year-long study on contaminated water related to potential risks for the local fruit industry, funded by Hortgro Science. It is no secret that the agricultural sector is genuinely concerned about the quality of water used for agricultural purposes as well as the public’s perceptions about it. “Water is a limited and scarce resource particularly in South Africa, we, therefore, need to look after it and manage it more effectively.”  The lack of good quality water can also be seen as a possible ‘barrier-to-trade’. “This is because fruit exported from developing countries like South Africa are often incorrectly perceived to be produced under unhygienic conditions or are considered of poor quality and safety.”

Public health threats are further increased due to an increase in immuno-compromised individuals, global procurement and movement of fresh produce. There has also been an increase of fresh produce consumption over the past twenty years, resulting in more cases of foodborne associated disease outbreaks. Given that the world has become an interconnected “global village” as well as the importance of our fruit being sold on the overseas markets, it is crucial that food safety is considered key to assured and sustained exports. Furthermore, it is paramount for local producers that public perception about the safety of our food supplies is not compromised. According to Korsten this is especially the case given the deteriorating quality of many of our freshwater resources, causing a real concern for producers and consumers.

Outbreaks of foodborne diseases in recent years highlighted the potential economic impact that food safety scares can have on farmers. In May 2011, for example, there was an outbreak of E. coli in the European Union that was initially pinned on Spanish cucumbers and tomatoes. Although it was later linked to a German sprout producer, Spanish farmers lost 225 million Euros per week because of the initial misdiagnoses. “Supermarkets are therefore very sensitive to any possible risks that might arise due to food safety factors,” says Korsten

Pathogen alert

Local producers should always be in “pathogen alert” mode, she says. This has been underlined by new scientific information due to a myriad of novel research techniques. New results obtained from her research team during the last two years highlight the importance of continued research to stay at the forefront of global innovation. Antimicrobial resistance is, for instance, emerging as a major global concern in public health, she says. “This aspect of plant-and-human health has major implications for food producers in the future.”

There are many pathogens that can cause foodborne disease outbreaks, including E. coli and Salmonella species. This is because waterborne pathogens can enter plants through growth cracks, roots and little openings in the fruit skin (stomata/lentils). Determining the level of risk associated with irrigation water used in the agricultural sector on deciduous fruit and grapes is therefore very important. Produce can be contaminated before, during and after harvest, including through organisms that are present in the soil and in irrigation water as well as when handled by humans. This is because water is used for irrigation purposes, in pesticide spray tank mixes, as a medium to cool fruit, transport and wash it, or to clean facilities and wash hands with. Contaminated water used could lead to the asymptomatic infection of people and animals, thereby increasing the risk of contamination of produce.

The science of unraveling risk

Korsten, heading up the Fresh Produce Food Safety team in the Department of Plant Science at the University of Pretoria, has led a multi-year research project for the local fruit industry on this issue. This project ran from 2006 to 2010. Scientists employed various molecular and other techniques to more accurately and rapidly identify pathogens. Water and fruit samples (including apples, pears, table grapes, plums, and peaches)were collected from selected farms, mainly in the Western Cape and Limpopo. These samples were analysed for the presence of Escherichia coli, Listeria monocytogenes, Salmonella enterica subsp enterica Typhimiuriuma and Staphyococcus aureus. These organisms are all serious pathogens that can cause foodborne diseases.

The fruit samples were spiked with waterborne pathogens to determine just how successful bacteria can attach to different fruit surfaces. The water samples were obtained from rivers, dams and pesticide spraying points in the region of Paarl (Bergriver), Drakenstein and Grabouw. The results provided valuable insights into the risk profile of the industry, says Korsten. High levels were detected of coliform bacteria in the water samples tested.  However, this on its own does not mean much. A more critical finding was that none of the more serious pathogens associated with foodborne of waterborne disease outbreaks were observed in the samples studied during this period. “Food safety concerns do not lie with farm water contamination only, but rather what happens further down the supply chain,” the researchers concluded. Generally, the number of pathogens present on fruit samples is much lower when compared with vegetable products. Korsten explains: “Fruit by its very nature as well as the production system has a lower risk for contamination than vegetables which are mostly grown in close proximity to the ground.” This is because vegetable crops like lettuce are for instance directly irrigated and at much higher risk than a product like table grapes (where the crop is not directly in contact with irrigation water).

In fruit production water does not generally come into direct contact with fruit in an orchard if crops are irrigated. This is particularly true when using a sprinkler, micro or drip irrigation under the trees or vines. It was found that if irrigation water does land on the fruit it tends to roll off and the pathogens do not generally attach. This is specifically true in cases of waxy and smooth fruit types. Very few farmers also irrigate directly out of rivers but rather use holding dams. This allows most pathogens to settle into the sediment below. The presence and persistence of pathogens on crops have been linked to crops’ surface characteristics (being hairy or smooth, etc). The fruits’ shape, as well as the thin layer and type of wax that covers for instance plums, are also some factors that play a role in effective microbial attachment. Basically, the ability of a pathogen to attach, colonise and survive on plant surfaces depends on the cultivar. This is linked to the nature of fruit peels. It is, for instance, easier for bacteria to latch onto a hairy peach than to a smooth plum.

Furthermore, if produce does get contaminated some (but not all) pathogens are also not likely to survive the local export chain due to harsh (cold) export conditions. Some organisms like Listeria monocytogenes can, however, survive at temperatures as low as 0.5°C in cold storage.

The way forward

Research has underlined the importance of food safety management systems for farmers, especially given current problems with water quality in the country. What can farmers do about this? “Firstly, ensure more effective implementation of international food safety standards and requirements, such as water quality management and effective hygiene and sanitation systems,” says Korsten. “Secondly, invest in human capital and contribute towards the training of a new cadre of young scientists in horticultural food safety. Go into partnership with research institutes doing cutting-edge research and provide financial support to these institutions of excellence. Establish an enabling platform to take the novel technology and new knowledge to the farm to ensure effective uptake and provision of real-time solutions.

“Furthermore, encourage the government to do the same and put pressure on local municipalities to ‘clean-up-their-act’ when it comes to wastewater management. Collective action between research institutions, farmers and the government, therefore, remains critical to protect local producers and consumers.” Appropriate water testing to ensure water is free of waterborne pathogens is also important, she says. “However, keep in mind that recent developments in water research technology and diagnostic test methods have been changing so rapidly that most of the traditional methods used in water and food laboratories are now outdated and obsolete, often providing inaccurate or meaningless results.”

“In my opinion, a lot of farmers are currently wasting their money with unnecessary testing of water and fruit samples if laboratories are using old technologies,” says Korsten. Water used in packhouses’ wash stations and in bathrooms on farms should also be managed effectively to ensure it is potable. “The effective washing of fruit (with the correct disinfectants) probably offers one of the best opportunities to get rid of newly introduced pathogens. This approach, if implemented rigorously, can provide a real-time solution similar to the concept of ‘hurdle-technology’ used in the food industry.” This does come ‘at a cost’ to producers (in terms of increased water replenishment rates and purification costs) and can negatively affect the water footprint of their produce.

Korsten says, “Contaminated water could still pose a food risk for waterborne pathogens. This is something that responsible producers should take very seriously, especially given emerging research on antimicrobial resistance.” And since some of the foodborne pathogens can attach and survive on certain fruit surfaces, it is important to consider certain interventions by focusing on applying crop protectants that are known to also inhibit the growth of some waterborne pathogens (such as Dithane, Copper hydroxide, Captan Flo and Prosper 500 EC).”

Although agricultural chemicals can be used to reduce the risk of pathogens on fruit, it is important to be aware that some of the chemicals can even support pathogen growth. “This should be taken into consideration in a risk assessment approach for each cultivar and spray program used on farms. Irrigate and use pesticides at the correct dosage, follow the described withholding periods and use the pesticide strategically to minimise waterborne pathogen growth.

(This article originally published by Hortgro Science 2016.)