Nanotech to make produce safer?

Nearly half of foodborne illnesses in the U.S. from 1998 through 2008 have been attributed to contaminated fresh produce. Prevention and control of bacterial contamination on fresh produce is critical to ensure food safety. The current strategy remains industrial washing of the product in water containing chlorine.

(an effective on-farm food safety program helps)

lettuceHowever, due to sanitizer ineffectiveness there is an urgent need to identify alternative antimicrobials, particularly those of natural origin, for the produce industry.

A team of researchers at Wayne State University have been exploring natural, safe and alternative antimicrobials to reduce bacterial contamination. Plant essential oils such as those from thyme, oregano and clove are known to have a strong antimicrobial effect, but currently their use in food protection is limited due to their low solubility in water. The team, led by Yifan Zhang, Ph.D., assistant professor of nutrition and food science in the College of Liberal Arts and Sciences, explored ways to formulate oil nanoemulsions to increase the solubility and stability of essential oils, and consequently, enhance their antimicrobial activity.

“Much of the research on the antimicrobial efficacy of essential oils has been conducted using products made by mixing immiscible oils in water or phosphate buffered saline,” said Zhang. “However, because of the hydrophobic nature of essential oils, organic compounds from produce may interfere with reducing the sanitizing effect or duration of the effectiveness of these essential oils. Our team set out to find a new approach to inhibit these bacteria with the use of oregano oil, one of the most effective plant essential oils with antimicrobial effect.”

Zhang, and then-Ph.D. student, Kanika Bhargava, currently assistant professor of human environmental sciences at the University of Central Oklahoma, approached Sandro da Rocha, Ph.D., associate professor of chemical engineering and materials science in the College of Engineering at Wayne State, to explore options.

“In our research, we discovered that oregano oil was able to inhibit common foodborne bacteria, such as E. coli O157, Salmonella and Listeria, in artificially contaminated fresh lettuce” said Zhang. “We wanted to explore the possibility of a nanodelivery system for the oil, which is an area of expertise of Dr. da Rocha.”

The team initially considered the use of solid polymeric nanoparticles for the delivery of the oil, but da Rocha suggested the use of nanoemulsions.

“My team felt the use of nanoemulsions would improve the rate of release compared to other nanoformulations, and the ability of the food grade surfactant to wet the surface of the produce,” said da Rocha. “We were able to reduce L. monocytogenes, S. Typhimurium, and E. coli O157 on fresh lettuce. Former Ph.D. student Denise S. Conti, now at the Generics Division of the FDA, helped design the nanocarriers and characterize them.”

The team added that while there is still work to be done, their study suggests promise for the use of essential oil nanoemulsions as a natural alternative to chemicals for safety controls in produce.

“Our future research aims to investigate the antimicrobial effects of essential oil nanoemulsions in various combinations, as well as formulate the best proportions of each ingredient at the lowest possible necessary levels needed for food application, which ultimately will aid in maintaining the taste of the produce.”

More information: The study, “Application of an oregano oil nanoemulsion to the control of foodborne bacteria on fresh lettuce” appears in the May 2015 issue of Food Microbiology.

Slowing bacteria’s ‘happy dance’ improves food safety

New nanotechnology developed by University of Guelph researchers that stops pathogenic bacteria from doing their happy dance might help improve food safety.

ListeriaIn an article published this week in the Royal Society of Chemistry’s Lab on a Chip Journal, the team describes nanotechnology used to study how food preservatives such as vinegar can control individual cells of Listeria monocytogenes.

In 2008, this bug killed 23 people after contaminating meat-processing equipment at Canadian-based Maple Leaf Foods.

Besides lead author Evan Wright, third-year biological engineering, the team consisted of Guelph engineering professor Suresh Neethirajan; Prof. Keith Warriner, Department of Food Science; and Scott Retterer and Bernadetta Srijanto, Oak Ridge National Laboratory in Tennessee.

In Neethirajan’s bio-nano lab, the researchers developed a nano-porous microfluidic device to see how individual Listeria cells respond to acetic acid (vinegar).

This technology is much more precise than traditional methods of measuring how preservatives affect microbes.

Adding more vinegar slowed the bacteria and made them move more randomly and with less end-over-end tumbling – what Neethirajan calls “dancing.” Those changes indicate stress, meaning that the bacteria are less able to make biofilms and become less infective.

“We know exactly at what moment the bacterial change in motility occurs in relationship to the change in concentration,” said Neethirajan.

Listeria can grow over a wide range of temperatures and withstand many stresses.

“This is a powerful technology with strong potential,” said Warriner, a microbiologist who has studied bacterial food outbreaks. “It’s a method of testing the mode of action of preservatives in food systems.”

He said this study can also help in looking at how antibiotic resistance develops in pathogens such as Salmonella, and how Listeria and other pathogens invade tissue to cause illness. He said food companies might use their work to improve food packaging and storage to inhibit bacterial growth.

Along with Maple Leaf Foods, the Guelph researchers are using the technology to study resistance to cleaners for food preparation surfaces.

Adam Vogt, a master’s student with Neethirajan, uses the model to study Helicobacter pylori, which is associated with stomach ulcers and spicy food. 

Nanoparticles: a new bug killer?

The use and overuse of antibiotics have, according to The Economist, led to bacteria evolving resistance to many medications. Dealing with multi drug-resistant strains of Staphylococcus aureus (which causes MRSA infections) and Escherichia coli (linked to food poisoning) requires complex and costly care. The emergence of totally drug-resistant tuberculosis threatens a return to a time before antibiotics, when many life-threatening conditions were largely untreatable.

fda-antibiotics-agricultureNanotechnology could be one way of avoiding, or at least postponing, such a nightmare. Many nanoparticles, which are substances smaller than 100 nanometres (billionths of a metre) have antimicrobial properties, disrupting bacteria and either preventing them from spreading or killing them outright. Silver nanoparticles, in particular, interfere with bacterial replication and the tiniest specks physically abrade and disrupt membrane walls. The most powerful nano-attacks, however, appear to involve reactive oxygen species (ROS). These chemically active molecules are the shock troops of the biological world, rampaging through DNA, oxidising enzymes and damaging many of the cells and proteins essential for life.

The problem is that the mechanisms that allow nanoparticles to kill bacteria pose a risk to the very people they are intended to protect. Inhaled nanoparticles of metal oxides or silver can persist in the lungs and migrate to the kidneys, liver and brain with toxic effects. And ROS have been linked to genetic damage, heart problems and Alzheimer’s disease.

Now Philip Demokritou and Georgios Pyrgiotakis at the Centre for Nanotechnology and Nanotoxicology at the Harvard School of Public Health have come up with a way of creating safer nanoparticles, literally from thin air, using a process called electrospraying. A cooling element chills a tiny needle to condense a minuscule drop of water vapour from the atmosphere. Applying a high voltage to the needle then explodes the drop into a spray of droplets, each just 25 nanometres in size, containing water and ROS.

How to regulate nanotechnology in food?

In 1959, a Nobel Prize-winning physicist challenged his colleagues to use submicroscopic particles to manufacture a wide range of products—an idea that captivated the imagination of scientists and inspired the science fiction movies “Fantastic Voyage” and “Innerspace.”

Fifty years later, “nano” (small) technology has moved from the science fiction realm to scientific fact, and federal regulators are laying the groundwork for monitoring a new generation of medical devices, drugs, cosmetics, and other products.

The U.S. Food and Drug Administration is continuing a dialogue on nanotechnology begun in 2011 by publishing proposed guidelines on the evaluation and use of nanomaterials in FDA-regulated products.

The first draft guideline, “Draft Guidance for Industry, Considering Whether an FDA-Regulated Product Involves the Application of Nanotechnology” was published in the Federal Register in June, 2011. The FDA is still reviewing and receiving comments on this document from the public.

In April 2012 the FDA is issuing two new draft guidelines for manufacturers of food substances and cosmetics, which are also open for public comment.

FDA Commissioner Margaret A. Hamburg, M.D., says the guidelines provide a starting point for the nanotechnology discussion. “Our goal is to regulate these products using the best possible science,” Hamburg says. “Understanding nanotechnology remains a top priority within the agency’s regulatory science initiative and, in doing so, we will be prepared to usher science, public health, and FDA into a new, more innovative era.”

Nanotechnology—the science of manipulating materials on a scale so small that they can’t be seen with a regular microscope—could have a broad range of applications, such as increasing the effectiveness of a particular drug or improving the packaging of food or altering the look and feel of a cosmetic.

“Guidance for Industry: Assessing the Effects of Significant Manufacturing Process Changes” describes factors industry should consider when determining whether a significant change in the manufacturing of a food substance affects its identity, safety or regulatory status (such as whether a substance is covered by an existing food additive regulation). A food substance is one that is added to food or to food packaging for purposes that include improving taste, texture, or shelf life.

This guidance covers “any manufacturing process change that might affect a food substance’s identity, intended uses, or the way it behaves in the body after it is eaten,” says Dennis Keefe, Ph.D., director of the Office of Food Additive Safety.

Keefe added that nanotechnology now is being studied in food packaging to combat bacteria and detect spoilage, and to improve the bioavailability (the degree and rate at which a substance is absorbed into one’s system) of nutrients, among other applications.