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Friday, April 15, 2022

Keeping apples fresh using clay films

Long-term food storage technology may help address potential food crises

NATIONAL INSTITUTE FOR MATERIALS SCIENCE, JAPAN

Appearance changes — IMAGE: EXTENT OF DECAY IN APPLES TREATED WITH CLAY FILM AND CLING WRAP view more
CREDIT: MIHARU EGUCHI NATIONAL INSTITUTE FOR MATERIALS SCIENCE EGUCHI.MIHARU@NIMS.GO.JP

An international research team consisting of NIMS, The University of Queensland and National Taiwan University has succeeded in creating a clay film with its gas permeability optimized for long-term storage of fresh produce by adjusting the sizes of the clay nanosheet particles comprising it. The team then uniformly coated the surfaces of various fruits with the film. This treatment kept the fruits’ respiration rates low without completely depriving them of oxygen, preventing them from decaying.

Efforts have been made to develop gas barrier films using clay nanosheets. Although some researchers attempted to improve the film properties of clay nanosheets by adding organic polymers to them, films can also be formed using only clay nanosheets without additives. Only a few studies had previously evaluated the physical properties of clay films composed solely of clay nanosheets.

This international joint research team focused on the gas permeability of clay films and found that a film composed of clay nanosheets with particle sizes in the range of several dozen nanometers (1 nm = one millionth of 1 mm) had relatively high permeability to gas molecules as they can pass through gaps between particles. This gas permeability is equivalent to that of plastic bags with minute pores used to store fresh produce. These bags are able to adequately reduce oxygen supply to fresh fruit, preventing it from ripening too rapidly. The gas permeability similarities between the clay film and the plastic bags inspired the research team to assess the ability of the clay film to preserve the quality of fresh produce for long periods of time.

In this research, the team applied a suspension of clay nanosheets to the surfaces of various fruits (e.g., apples, bananas and oranges) to form uniform films on their surfaces. The team also prepared untreated fruits and fruits covered in cling wrap for comparison. The gas emissions and appearance of these treated and untreated fruits were monitored for several months. As shown in the figure below, the untreated apples (the first photo from the left) had decayed by the end of the experimental period and the apples covered only in cling wrap (the fourth photo from the left) had also decayed and grown mold. By contrast, the apples coated with the clay film (the two middle photos) did not decay or grew mold, presumably because the film reduced the external oxygen supply needed for ripening and mold growth. In addition, the clay film was confirmed to be in tight contact with the surfaces of the apples it coated, suggesting that it may be able to effectively block the diffusion of ethylene into the air, a phytohormone which plays an important role in inducing fruit ripening.

In addition to its potential ability to restrict the external oxygen supply and ethylene diffusion, the clay film may be able to prevent odor compounds produced by fresh produce from diffusing into the air, possibly making them less attractive to pests. In future research, the team plans to improve the ease of application and strength of the clay film to make it more suitable for preserving the quality of fresh produce during its transportation to the market.

This project was carried out by an international joint research team consisting of Miharu Eguchi (Senior Researcher, Mesoscale Materials Chemistry Group, International Center for Materials Nanoarchitectonics, NIMS) and researchers from The University of Queensland and National Taiwan University. This work was supported in part by JST-ERATO Yamauchi Materials Space-Tectonics Project.

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This research was published in Journal of Materials Chemistry A (the January 28, 2022 issue, pp. 1956-1964).

JOURNAL

Journal of Materials Chemistry A

DOI

10.1039/D1TA08837H

METHOD OF RESEARCH

Experimental study

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

Highly adhesive and disposable inorganic barrier films: made from 2D silicate nanosheets and water

Surfing at the atomic scale: Scientists experimentally confirm new fundamental law for liquids

by Australian Nuclear Science and Technology Organisation (ANSTO)

The first experimental evidence to validate a newly published universal law that provides insights into the complex energy states for liquids has been found using an advanced nuclear technique at ANSTO.

The work has just been published in the Journal of Physical Chemistry Letters as the editor's choice and featured on the front cover of the journal.

The equation for the vibrational density of states formulated by Alessio Zaccone and Matteo Bagglioli was published in a paper in PNAS in 2021, providing an answer to a question that has been elusive for at least a century.

The elegant mathematical theory has solved the problem of obtaining the distribution of these complex energy states for liquids.

"One of the most important quantities in the physics of matter is the distribution of the frequencies or vibrational energies of the waves that propagate in the material. It is particularly important as it is the starting point for calculating and understanding some fundamental properties of matter, such as specific heat and thermal conductivity, and the light-matter interaction, "said Prof Zaccone on the University of Milan website.

"The big problem with liquids is that, in addition to acoustic waves, there are other types of vibrational excitations related to low energies of the disordered motion of atoms and molecules— excitations that are almost absent in solids. These excitations are typically short-lived and are linked to the dynamic chaos of molecular motions but are nevertheless very numerous and important, especially at low energies. Mathematically, these excitations, known as 'instantaneous normal modes' or INMs in the specialized literature are very difficult to deal with as they correspond to energy states described by imaginary numbers."

The time-of-flight neutron spectrometer Pelican at ANSTO's Center for Neutron Scattering has been used to measure the vibrational densities of states for several liquid systems including water, liquid metal, and polymer liquids. The Pelican instrument has the extreme sensitivity to measure rotational and translational vibrations over short time intervals and at low energies.

The experiments at ANSTO confirmed the linear relationship of the vibrational density of states with frequency at low energies as predicted by Alessio Zaccone and Matteo Bagglioli, as shown in the figure below.

With the COVID lockdown, no accessibility to instruments, the small team that included University of Wollongong Ph.D. candidate Caleb Stamper, Dr. Cortie and Dr. Yu decided to focus on re-analyzing past experimental data from a new perspective, to validate the new law, inspired by the theoretical work from Alessio Zaccone and Matteo Bagglioli.

"The exercise not only achieves such a great outcome but also provides a good introduction of neutron spectroscopy to Caleb, who has done an excellent job," said Dr. Yu as Caleb's ANSTO supervisor and the corresponding author of the paper.

The work would also help them address questions relating to phase transitions in superionic liquids in their work on thermoelectric materials.

"Major challenges arise because liquids are not mechanically stable, as the atoms in a liquid diffuse and the liquid as a whole will flow," explained Dr. Cortie.

The universal law is based on a theoretical framework, known as instantaneous normal modes, as described by Prof Zaccone above, which prescribe a set of instantaneous forces, frequencies, and velocities as quantities.

A complication in deriving a theory to predict the vibrational density of states in liquids arose because of the presence of a small fraction of "imaginary modes."

"Imaginary modes are important because they represent the fact that a liquid is not stable. The atoms in a liquid are strongly interacting with one another all the time but not in the same way a solid does. The relationship is not 'harmonic' meaning that the atoms are not going to be restored to the same configuration after an interaction. The atoms will continue to diffuse quickly and slide past each other," said Stamper.

"The imaginary modes reflect the negative curvature on the potential energy surface of a liquid. It is a very complex energy landscape but if you think of the analogy of a surfer on an ocean wave. The atoms in the liquid follow the curves of the wave itself (see the front cover of the journal). But the atoms can be in a position on the crest, under the surfboard or in the trough, always moving," said Dr. Yu.

"The law will play, for liquids, the same pivotal role that the Debye law plays for solids. It will serve as the foundation for the whole research field involving liquids and beyond.Molecular 'dances' determine how liquids take up heat

More information: Caleb Stamper et al, Experimental Confirmation of the Universal Law for the Vibrational Density of States of Liquids, The Journal of Physical Chemistry Letters (2022). DOI: 10.1021/acs.jpclett.2c00297

Alessio Zaccone et al, Universal law for the vibrational density of states of liquids, Proceedings of the National Academy of Sciences (2021). DOI: 10.1073/pnas.2022303118

Journal information: Proceedings of the National Academy of Sciences , Journal of Physical Chemistry Letters

Provided by Australian Nuclear Science and Technology Organisation (ANSTO)

USA

New study provides guidance for reconsidering harmful place names in national parks

Peer-Reviewed Publication

OREGON STATE UNIVERSITY

In a new study examining the origins of more than 2,000 place names in 16 U.S. national parks, researchers have developed a tool for evaluating and changing names that may be harmful or rooted in white supremacy.

Oregon State University associate professor Natchee Barnd is a co-author of “Words Are Monuments,” published last week in the journal People and Nature. The intent of the paper is to open a conversation about place names, rather than defaulting to the assumption that those names are neutral, he said.

“There’s a process by which those names are chosen,” said Barnd, whose work focuses partly on Indigenous geography. “And if we’re operating within a system that has been grounded in white supremacy, it’s probably going to reflect that — some really explicitly and vehemently, and some by default or accidentally, such as the fact that a name is in English.”

That doesn’t mean all names need to be immediately changed, he said, but researchers sought to provide a tool people can use to think about how those names came to be.

While the work focused on national parks, the authors expect the categorization tool they developed to be applicable for people or institutions in any location seeking to improve naming practices.

For the study, researchers analyzed 2,241 place names in 16 national parks across the U.S., from Acadia in Maine to Hawai’i Volcanoes in Hawai’i. They created “decision trees” to classify name meanings into different categories, which allowed them to group together place names with similar origins so they could find and describe patterns in naming across parks in a consistent way.

Classifications included language origin; derogatory (involving use of a racial slur); erasure (such as replacement of Indigenous names); and dimensions of racism and colonialism.

All 16 parks contained at least one place or feature named after people who supported racist ideologies, capitalized on Indigenous colonization and/or participated in acts of genocide, the study said.

Researchers found 107 natural features with traditional Indigenous place names. They classified 214 names as appropriation, where Indigenous or Indigenous-sounding names were used incorrectly and without Indigenous input or consent; and 254 names that memorialize settler colonialism, such as Cadillac Mountain in Acadia, named for a French colonizer.

They found 21 names that commemorate individuals who espoused racist ideas, including Hayden Valley in Yellowstone, named for Ferdinand Hayden, a geologist who wrote that unless Native Americans were forcefully assimilated, “they must ultimately be exterminated.”

More nuanced were the 364 names that researchers classified as European (non-Indigenous) in origin with no record of their meaning, including descriptive names like Clear Creek and Long Pond.

“One goal is to open up the conversation and getting to the place of saying that these names are not neutral; they are values being represented in some way,” Barnd said. “Maybe we find out that the name has this whole history we don’t know about. It’s about trying to find intention, to trace a lineage. But you have to use a scientific process to sort through these names.”

This undertaking should be a collaborative process, he said. For example, in Oregon, a coalition of local agencies led by the Marys Peak Alliance recently worked with the Siletz and Grand Ronde tribes to pick names for some unnamed creeks on Marys Peak, just west of Corvallis.

The next step, after reconsidering place names and potentially replacing them with traditional Indigenous history in mind, will be returning ownership to the tribes as well, Barnd said.

National parks provide a perfect starting point for this process, he said. The parks have a long history of co-management with tribes, including deferring to tribal knowledge for how best to manage the land and resources, and substantial numbers of tribal members working in national parks.

“There are places where we can do things differently,” Barnd said. “Names are part of how we create the world we live in and believe in and understand. They’re not just there; we’re creating that meaning, which is also creating the meaning of ourselves.”

Co-authors on the study were Bonnie McGill, Stephanie Borelle, Grace Wu, Kurt Ingeman and Jonathan Uhuad Koch from the Society for Conservation Biology in Washington, D.C.