Microbes are everywhere. Their ability to adapt to environmental conditions means they can survive on surfaces and enter the food manufacturing chain where they continue to multiply. This presents a daunting uphill battle for food manufactures to maintain hygiene and prevent contamination.
Of the more than 200 pathogenic organisms that cause foodborne illness, Listeria monocytogenes is among the most concerning for public health.
The team of Dr. Aliyar Cyrus Fouladkhah, Associate Professor at Tennessee State University, has pioneered validation studies offering invaluable insights into how high-pressure techniques can be adapted to decontaminate food such as ready-to-eat products. In doing so their work is and will be instrumental in making the food we eat safe and improving public health in the USA and worldwide.
Read the original article: https://doi.org/10.3390/microorganisms12091858
Image Source: Adobe Stock Images / digicomphoto
Transcript
Hello and welcome to Research Pod. Thank you for listening and joining us today.
In this episode, we will be learning about the foodborne illness, Listeriosis and the emerging processing technology used to prevent it. Despite tight regulations particularly in developed countries, fatal outbreaks of Listeriosis still occur globally. This highlights the urgent need for improved decontamination techniques to prevent one of the deadliest foodborne illnesses.
Critical to this work is the research of Dr. Aliyar Cyrus Fouladkhah, Associate Professor at Tennessee State University. His team’s pioneering validation studies are offering invaluable insights into how high-pressure techniques can be adapted to decontaminate food such as ready-to-eat products. In doing so their work is and will be instrumental in making the food we eat safe and improving public health in the USA and worldwide.
Microbes are everywhere. Their ability to adapt to environmental conditions means they can survive on surfaces and enter the food manufacturing chain where they continue to multiply. This presents a daunting uphill battle for food manufactures to maintain hygiene and prevent contamination. Of the more than 200 pathogenic organisms that cause foodborne illness, Listeria monocytogenes is among the most concerning for public health.
Over 99% of Listeria monocytogenes outbreaks are foodborne with raw milk and its associated products, ready-to-eat foods, vegetables, juices and fish at high risk. Able to survive and even multiply at temperatures from zero to 45°C and in PH ranges of 4 to 9.5, refrigerated or even acidic products can be contaminated. Furthermore, consumers may not detect contaminated food because often it does not smell or taste off. This bacterium is ubiquitous and can be found in food manufacturing areas. As part of the environmental monitoring programme in the USA, manufacturers are required to test all ready-to-eat products for Listeria. Refrigerated products with prolonged shelf lives such as smoked fish can harbour high levels of the bacteria and in 2022, 17 cases of Listeriosis in multiple countries in Europe were linked to smoked fish.
The incubation period of Listeria monocytogenes was believed to range between 3-70 days with a median of 21 days, but recent studies suggest that on average it takes 11 days from ingestion to the onset of symptoms. General symptoms of infection include fever, confusion, headaches and muscle pain but can worsen to septicaemia and meningitis. Groups that are most susceptible and at risk of severe illness are the elderly (those over 65 years old), very young (those under 5 years old), immunocompromised and pregnant women. Pregnant women are ten times more likely to contract Listeria and infection, which can result in miscarriage, premature births, stillbirths, or neonatal infection.
From 1998 to 2017, the centres for disease control and prevention detected at least 77 outbreaks of Listeriosis in the USA alone with a 78% hospitalization and 20% fatality rate. Similar epidemiological trends are seen in Europe while in South Africa in 2018, the largest outbreak of any foodborne pathogen in recorded history occurred. Nine hundred and thirty-seven people were infected after eating processed meat half of those were pregnant women. Of the patients with a known outcome, 27% died. Considering the significant risk of severe disease and fatality from Listeriosis, stringent food manufacturing processes need to be in place to prevent further outbreaks.
So, what can be done to remove these bacteria from our food? Well commonly, extreme thermal or heat processing is used to inactivate foodborne bacteria. However, while effective, this method reduces the quality and nutritional value of food, so alternative techniques are needed. The last decade has brought advances in food manufacturing technology and with-it new possibilities to prevent foodborne outbreaks. One of these techniques is high-pressure processing where intense pressure is applied to food to disrupt bacteria physiology and induce cell death. These techniques are revolutionising the field by providing the double benefit of decontamination and preservation of food freshness and nutrition.
As the market for ready-to eat products grows so does the demand for effective high-pressure techniques. By 2018, sales of foods treated with high pressure had surpassed $9 billion in the USA alone. The private food industry commonly uses a pressure of 600MPa to decontaminate, but such extreme pressures can affect food quality and are expensive to run. Scientists therefore need to figure out the optimal set of conditions for maximum decontamination without unnecessary excessive pressure. This would reduce processing costs and preserve the shelf life of pressure tools enabling widespread and sustainable implementation of these techniques. Importantly, reduced pressure would preserve the quality and nutritional value of treated foods.
Working to crack the formulae, Fouladkhah and team conduct what are known as microbiological hurdle validation studies. Hurdle studies are a holistic approach combining methods which are otherwise ineffective on their own against foodborne bacteria. This synergistic approach aims to eliminate bacteria by determining the best combination of physical, physiochemical and microbial conditions for maximum decontamination.
Of the many factors scientists consider in the food decontamination process, three are key. These are temperature, intensity of pressure and use of antimicrobial agents. A major focus of Fouladkhah’s research over the last decade is to determine the most effective combination of these factors for decontamination while reducing the pressures used. One of these factors, mild heat typically 55 to 60°C is vital to the process and its addition inactivates Listeria monocytogenes in raw milk, orange juice and smoked fish. The researcher’s study in smoked trout, a food product particularly susceptible to Listeria monocytogenes confirmed this synergistic decontamination effect of high-pressure and mild heat. This process also removed background microbiota to prolong the product’s shelf-life.
With the importance of mild heat established for decontamination of Listeria monocytogenes, the team extended their research to include Listeria innocua and Staphylococcus aureus. They tested two different pressures at a low and high temperature in both milk and orange juice. This study answered several questions. Firstly, it reconfirmed previous findings that addition of mild heat, in this experiment 60°C to high-pressure treatments significantly enhances decontamination. It also confirmed this decontamination ability extends to other microbes such as Listeria innocua and Staphylococcus aureus. These similar effects mean the non-pathogenic Listeria innocua could be used as a surrogate for monocytogenes in validation studies of similar scope, a finding that has been reconfirmed in their latest study. Use of a surrogate reduces the risk of contaminating food manufacturing plants and laboratories with a pathogenic species. Decontamination of Staphylococcus aureus by the same process demonstrates its multiple beneficial effects in pathogen control.
One concern about the use of high-pressure techniques is that a subset of Listeria monocytogenes can survive the process, these are known as pressure-stressed bacteria. A further subset known as the habituated phenotype demonstrate a reduced response to pressure following repeated stimulations. Little is known about what happens to these bacteria, their ability to proliferate and if they demonstrate similar sensitivity to different decontamination processes compared with wildtypes. The team confirmed in two separate studies that these phenotypes do exhibit similar sensitivity to the tested processes despite their previous exposure.
Another important element is the addition of antimicrobial agents such as Nisin. Nisin, a naturally occurring antimicrobial peptide produced by the bacterium Lactococcus lactis has long been used in food manufacturing to eliminate Gram positive bacteria such as Listeria monocytogenes. However, little was known about its efficacy during high-pressure processing under controlled temperature and conditions. Aiming to fill this knowledge gap, Fouladkhah added nisin as a third hurdle to his validation studies. The addition of nisin to mild heat and high-pressure treatments boosted the decontamination of Listeria monocytogenes creating a ‘super synergistic effect’. However, this study was conducted in phosphate buffer solution and will require validation in food products.
Shifting focus from decontamination processes to packaging in the manufacturing chain, the team wanted to determine if adding nisin to smoked trout reduced Listeria monocytogenes counts during the product’s 4-week shelf life. They found Nisin was effective in removing approximately 90% of the pathogen during the initial storage period but its effects declined over time. While promising, the findings are a reminder of the importance of complete elimination of the pathogen before the product reaches supermarket shelves to prevent outbreaks.
This research demonstrates that decontamination of Listeria monocytogenes is feasible when using reduced pressure if other factors are included and controlled in the process. Commenting in the conclusion of their research paper published in the journal Microorganisms, Fouladkhah wrote.
“These results illustrate that high-pressure processing and thermally assisted high-pressure processing can be used effectively for the reduction of pathogens of public health concern and reducing background microbiota for extension of this product’s shelf life.”
The team will continue their work in advancing and optimising these techniques to improve food safety and maintain quality and freshness all while reducing manufacturing costs. The goal being to translate laboratory-based research into tangible solutions for public health.
That’s all for this episode – thanks for listening and stay subscribed to Research Pod for more of the latest science.
See you again soon.
Leave a Reply