Tag Archives: Kee Woei Ng

Cellulose nanocrystals (CNC), protein, and starch eletrospun to develop ‘smart’ food packaging

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A December 29, 2021 news item on ScienceDaily announces research into ;smart’ sustainable packaging from a joint Nanyang Technical University and Harvard University,

A team of scientists from Nanyang Technological University, Singapore (NTU Singapore) and Harvard T.H. Chan School of Public Health, US, has developed a ‘smart’ food packaging material that is biodegradable, sustainable and kills microbes that are harmful to humans. It could also extend the shelf-life of fresh fruit by two to three days.

The waterproof food packaging is made from a type of corn protein called zein, starch and other naturally derived biopolymers, infused with a cocktail of natural antimicrobial compounds. These include oil from thyme, a common herb used in cooking, and citric acid, which is commonly found in citrus fruits.

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A December 28, 2021 Nanyang Technological University press release (PDF), also on EurekAlert but published December 27, 2021, which originated the news item, offers a few more details about the research (Note 1: Links have been removed; Note 2: I had to dig into the abstract to find the cellulose nanocrystals),

In lab experiments, when exposed to an increase in humidity or enzymes from harmful bacteria, the fibres in the packaging have been shown to release the natural antimicrobial compounds, killing common dangerous bacteria that contaminate food, such as E. Coli and Listeria, as well as fungi.

The packaging is designed to release the necessary miniscule amounts of antimicrobial compounds only in response to the presence of additional humidity or bacteria. This ensures that the packaging can endure several exposures, and last for months.

As the compounds combat any bacteria that grow on the surface of the packaging as well as on the food product itself, it has the potential to be used for a large variety of products, including ready-to-eat foods, raw meat, fruits, and vegetables.

In an experiment, strawberries that were wrapped in the packaging stayed fresh for seven days before developing mould, compared to counterparts that were kept in mainstream fruit plastic boxes, which only stayed fresh for four days.

The invention is the result of the collaboration by scientists from the NTU-Harvard T. H. Chan School of Public Health Initiative for Sustainable Nanotechnology (NTU-Harvard SusNano), which brings together NTU and Harvard Chan School researchers to work on cutting edge applications in agriculture and food, with an emphasis on developing non-toxic and environmentally safe nanomaterials.

The development of this advanced food packaging material is part of the University’s efforts to promote sustainable food tech solutions, that is aligned with the NTU 2025 strategic plan, which aims to develop sustainable solutions to address some of humanity’s pressing grand challenges.

Professor Mary Chan, Director of NTU’s Centre of Antimicrobial Bioengineering, who co-led the project, said: “This invention would serve as a better option for packaging in the food industry, as it has demonstrated superior antimicrobial qualities in combatting a myriad of food-related bacteria and fungi that could be harmful to humans. The packaging can be applied to various produces such as fish, meat, vegetables, and fruits. The smart release of antimicrobials only when bacteria or high humidity is present, provides protection only when needed thus minimising the use of chemicals and preserving the natural composition of foods packaged.”

Professor Philip Demokritou, Adjunct Professor of Environmental Health at Harvard Chan School, who is also Director of Nanotechnology and Nanotoxicology Center and Co-director of NTU-Harvard Initiative on Sustainable Nanotechnology, who co-led the study, said: “Food safety and waste have become a major societal challenge of our times with immense public health and economic impact which compromises food security. One of the most efficient ways to enhance food safety and reduce spoilage and waste is to develop efficient biodegradable non-toxic food packaging materials. In this study, we used nature-derived compounds including biopolymers, non-toxic solvents, and nature-inspired antimicrobials and develop scalable systems to synthesise smart antimicrobial materials which can be used not only to enhance food safety and quality but also to eliminate the harm to the environment and health and reduce the use of non-biodegradable plastics at global level and promote sustainable agri-food systems.” 

Providing an independent assessment of the work done by the NTU research team, Mr Peter Barber, CEO of ComCrop, a Singapore company that pioneered urban rooftop farming, said: “The NTU-Harvard Chan School food packaging material would serve as a sustainable solution for companies like us who want to cut down on the usage of plastic and embrace greener alternatives. As ComCrop looks to ramp up product to boost Singapore’s food production capabilities, the volume of packaging we need will increase in sync, and switching to a material such as this would help us have double the impact. The wrapping’s antimicrobial properties, which could potentially extend the shelf life of our vegetables, would serve us well. The packaging material holds promise to the industry, and we look forward to learning more about the wrapping and possibly adopting it for our usage someday.”

The results of the study were published in the peer-reviewed academic journal ACS Applied Materials & Interfacesin October [2021].

Cutting down on packaging waste

The packaging industry is the largest and growing consumer of synthetic plastics derived from fossil fuels, with food packaging plastics accounting for the bulk of plastic waste that are polluting the environment.

In Singapore, packaging is a major source of trash, with data from Singapore’s National Environment Agency showing that out of the 1.76 million tonnes of waste disposed of by domestic sources in 2018, one third of it was packaging waste, and over half of it (55 per cent) was plastic.

The smart food package material, when scaled up, could serve as an alternative to cut down on the amount of plastic waste, as it is biodegradable. Its main ingredient, zein, is also produced from corn gluten meal, which is a waste by-product from using corn starch or oils in order to produce ethanol.

The food packaging material is produced by electrospinning[1] the zein, the antimicrobial compounds with cellulose, a natural polymer starch that makes up plant cell walls, and acetic acid, which is commonly found in vinegar.

Prof Mary Chan added: “The sustainable and biodegradable active food packaging, which has inbuilt technology to keep bacteria and fungus at bay, is of great importance to the food industry. It could serve as an environmentally friendly alternative to petroleum-based polymers used in commercial food packaging, such as plastic, which have a significant negative environmental impact.”

Prof Demokritou added: “Due to the globalisation of food supply and attitude shift towards a healthier lifestyle and environmentally friendly food packaging, there is a need to develop biodegradable, non-toxic and smart/responsive materials to enhance food safety and quality. Development of scalable synthesis platforms for developing food packaging materials that are composed of nature derived, biodegradable biopolymers and nature inspired antimicrobials, coupled with stimuli triggered approaches will meet the emerging societal needs to reduce food waste and enhance food safety and quality.”

The team of NTU and Harvard Chan School researchers hope to scale up their technology with an industrial partner, with the aim of commercialisation within the next few years.

They are also currently working on developing other technologies to develop biopolymer-based smart food package materials to enhance food safety and quality.

Here’s a link to and a citation for the paper, followed by the key (nanocellulose crystal mention) sentences in the abstract,

Enzyme- and Relative Humidity-Responsive Antimicrobial Fibers for Active Food Packaging by Zeynep Aytac, Jie Xu, Suresh Kumar Raman Pillai, Brian D. Eitzer, Tao Xu, Nachiket Vaze, Kee Woei Ng, Jason C. White, Mary B. Chan-Park, Yaguang Luo, and Philip Demokritou. ACS Appl. Mater. Interfaces 2021, 13, 42, 50298–50308 I: https://doi.org/10.1021/acsami.1c12319 Publication Date: October 14, 2021 Copyright © 2021 American Chemical Society

This paper is behind a paywall.

Excerpt from abstract,

Active food packaging materials that are sustainable, biodegradable, and capable of precise delivery of antimicrobial active ingredients (AIs) are in high demand. Here, we report the development of novel enzyme- and relative humidity (RH)-responsive antimicrobial fibers with an average diameter of 225 ± 50 nm, which can be deposited as a functional layer for packaging materials. Cellulose nanocrystals (CNCs) [emphasis mine], zein (protein), and starch were electrospun to form multistimuli-responsive fibers that incorporated a cocktail of both free nature-derived antimicrobials such as thyme oil, citric acid, and nisin and cyclodextrin-inclusion complexes (CD-ICs) of thyme oil, sorbic acid, and nisin. …

I have been following the CNC story for some time. If you’re curious, just use ‘cellulose nanocrystal(s)’ as your search term. You can find out more about ComCrop here.

Nanosunscreens, zinc oxide, cancer, and the latest research

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Researchers in Singapore (Nanyang Technological University and the National University of Singapore) have published a study suggesting that nano zinc oxide, found in some sunscreens, may potentially cause cancer. The Nov. 29, 2011 news item on Nanowerk provides this detail,

The chemical, Zinc Oxide, is used to absorb harmful ultra violet light. But when it is turned into nano-sized particles, they are able to enter human cells and may damage the cells’ DNA. This in turn activates a protein called p53, whose duty is to prevent damaged cells from multiplying and becoming cancerous. However, cells that lack p53 or do not produce enough functional p53 may instead develop into cancerous cells when they come into contact with Zinc Oxide nanoparticles. [emphases mine]

I was able to access the study and while I’m not an expert by any means I did note that the study was ‘in vitro’, in this case, the cells were on slides when they were being studied. It’s impossible to draw hard and fast conclusions about what will happen in a body (human or otherwise) since there are other systems at work which are not present on a slide.

A few items I was not able to determine (it’s in the study but I don’t understand the term ‘sonicate’ or others the researchers used),

  • were the concentrations of nano zinc oxide used in the research the standard concentrations one would find in a sunscreen, and
  • were the cells continuously exposed to nano zinc oxide, e.g. sitting in a bath of the chemical, or were the cells exposed in the way cells in a body would be exposed

I ask these questions not to so much to expose my ignorance but to point out how difficult it is draw conclusions from a study when you don’t have the training for it. In fact, if you read the news item on Nanowerk or the study (The role of the tumor suppressor p53 pathway in the cellular DNA damage response to zinc oxide nanoparticles [article behind paywall]), you’ll notice that even the researchers have phrased their findings very carefully.

You’ll also notice that there is another agenda (from the news item on Nanowerk),

The breakthrough also validated efforts by Asst Prof Loo and Asst Prof Ng to pioneer a research group in the emerging field of nanotoxicology, which is still very much in its infancy throughout the world.

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The research team would also like to work with the European Union to uncover the risks involving nanomaterials and how these materials should be regulated before they are made commercially available. Asst Prof Joachim Loo, who received his Bachelor and Doctorate degrees from NTU, was the only Singaporean representative in a recent nanotechnology workshop held in Europe. At the workshop, it was agreed that research collaborations in nanotoxicology between EU and South-east Asia should be increased.

Another research study on nano zinc oxide was released last year (it was not cited in the references for the latest Nov. 2011 study). From the Aug. 20, 2010 news item on physorg.com,

A technique developed by Macquarie University has proven for the first time that a tiny amount of zinc from sunscreens is absorbed through the skin into the human body, but is not yet able to discern whether the zinc is in nanoparticle form.

Professor Brian Gulson of Macquarie University conducted the research – published online in the current edition of the journal Toxicological Sciences – with collaborators in CSIRO and the Australian National University and the Australian Photobiology Testing Facility. The research was widely reported on in February 2010 following a presentation by Gulson at a scientific conference.

The team traced the skin absorption of a highly purified and stable isotope which allowed them to distinguish the zinc from the sunscreen from that which is naturally present in the body or environment. Zinc is absolutely essential to bodily functions.

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The researchers suggest that follow-up studies from the scientific community with different formulations over longer periods of time are essential, but that until evidence to the contrary is obtained, people spending time outdoors should continue to use sunscreens.

Getting back to that question about the concentration of the nano zinc oxide solution used in the most recent studies in Singapore, here’s what Brian Gulson had to say about nano zinc oxide concentrations in his work and about a shortcoming in his study (from an Australian Broadcasting Corporation [ABC] Feb. 25, 2010 interview with Ashley Hall,

BRIAN GULSON: I guess the critical thing was that we didn’t find large amounts of it getting through the skin. The sunscreens contain 18 to 20 per cent zinc oxide usually and ours was about 20 per zinc. So that’s an awful lot of zinc you’re putting on the skin but we found tiny amounts in the blood of that tracer that we used.

ASHLEY HALL: So is it a significant amount?

BRIAN GULSON: No, no it’s really not.

ASHLEY HALL: But Brian Gulson is warning people who use a lot of sunscreen over an extended period that they could be at risk of having elevated levels of zinc.

BRIAN GULSON: Maybe with young children where you’re applying it seven days a week, it could be an issue but I’m more than happy to continue applying it to my grandchildren.

ASHLEY HALL: This study doesn’t shed any light on the question of whether the nano-particles themselves played a part in the zinc absorption.

BRIAN GULSON: That was the most critical thing. This isotope technique cannot tell whether or not it’s a zinc oxide nano-particle that got through skin or whether it’s just zinc that was dissolved up in contact with the skin and then forms zinc ions or so-called soluble ions. So that’s one major deficiency of our study.

Of course, I have a question about Gulson’s conclusion  that very little of the nano zinc oxide was penetrating the skin based on blood and urine samples taken over the course of the study. Is it possible that after penetrating the skin it was stored in the cells  instead of being eliminated?

It seems it’s not yet time to press the panic button since more research is needed for scientists to refine their understanding of nano zinc oxide and possible health effects from its use.

Final note: The researchers listed on the Singapore study are: Kee Woei Ng, Stella P.K. Khoo, Boon Chin Heng, Magdiel I. Setyawati, Eng Chok Tan, Xinxin Zhao, Sijing Xiong, Wanru Fang, David T. Leong, and Joachim S.C. Loo