Food freezing and preservation may be headed for a “green” revolution. Scientists from the Agricultural Research Service (ARS) of the US Department of Agriculture (USDA) and the University of California Berkeley (UCB) have teamed up to develop a new way to preserve food that offers energy-saving, carbon-reducing and quality advantages over conventional freezer technologies.
The researchers’ innovation is to shift from conventional (isobaric) freezing to isochoric (constant-volume) freezing. Conventional freezing exposes food to air and freezes it solid at temperatures below 32 degrees F whereas the new method, isochoric freezing, preserves food at cold temperatures without freezing it solid.
The researchers had observed the fundamental relationship between temperature and pressure in liquids. Exposed to low temperatures, liquids tend to expand. Confining water in “constrained-volume contexts”—rigid, sealed containers that don’t allow liquids to expand as the temperature drops and pressure builds—can limit ice formation while recent experiments have shown that “macroscopic (visible to the naked eye) confinement” restrains ice growth and alters kinetic (movement-related) behavior. These discoveries laid the foundation for the new, breakthrough system.
The research team’s isochoric freezing method seals food in a rigid plastic or metal container that is completely filled with water or other liquids, allowing only a fraction of the liquid to freeze while the rest remains under high pressure—isochoric freezing requires that the volume of the liquid remains constant in a tightly closed system. According to the ARS, isochoric freezing thus avoids the biggest threat to food quality in conventional freezing: ice crystallization that leaves food dry and damaged. This makes isochoric freezing beneficial for preserving all kinds of foods, especially certain fresh produce, such as potatoes, cherries, and tomatoes, that don’t fare well with conventional freezing.
There are energy benefits too. "A complete changeover to this new method of food freezing worldwide could cut energy use by as much as 6.5 billion kilowatt-hours each year while reducing the carbon emissions that go along with generating that power by 4.6 billion kg, the equivalent of removing roughly one million cars from roads," said ARS food technologist Cristina Bilbao-Sainz, who works at the USDA’s Healthy Processed Foods Research Unit, a division of ARS's Western Regional Research Center (WRRC) in Albany, California.
Bilbao-Sainz goes on to say that freezing food solid, and maintaining it in that state, takes a tremendous amount of energy compared with isochoric freezing. Their new method also avoids energy-intensive quick-freezing methods that are used to avoid the formation of ice crystals.
Moreover, the technology may not be as disruptive as it sounds. Bilbao-Sainz thinks their technology, if adopted as conceived, can be employed without “any significant changes” to already established frozen food manufacturing equipment and infrastructure.
Health and food-safety benefits are achieved with the new method as well. According to the study, which appeared in the journal, Renewable and Sustainable Study Reviews, isochoric freezing kills harmful microbes during processing.
The benefits of the new method are such that adaptation could lead to “the next revolution in freezing foods."
Considering the broad array of benefits associated with isochoric freezing, it is easy to see why the developers are looking for opportunities to advance its acceptance and adaptation. WRRC center director and co-leader of the study, Tara McHugh, said in a February 2022 ARS bulletin, "The entire food production chain could use isochoric freezing.” That includes growers, food processors, product producers, wholesalers and retailers. In other words, this revolutionary form of freezing could be part of every step on the way from farm to table. McHugh says their method can actually be used in a home freezer without requiring a significant investment in new equipment. She believes the benefits of the method are such that adaptation could lead to “the next revolution in freezing foods.”
ARS credits Boris Rubinsky, a UCB biomedical engineer, for developing the team’s isochoric supercooling model, which was initially created to preserve tissues and organs for transplantation. Hence, the technology has great biomedical application potential for preserving tissues and organs that are short-lived outside of the human body and typically preserved for one or two days using expensive cryopreservation techniques.
Isochoric preservation has the potential to extend tissue preservation for many days without structural damage to the tissue and without needing the use of expensive cryoprotectants—substances that inhibit damage from freezing—such as dimethyl sulfoxide (DMSO) or glycerol.
Matthew Powell-Palm, one of the UCB engineers on the team and a lead author of the study, thinks the new method could even be useful to the space industry. It isn’t hard to imagine its potential for food and bio-preservation on long space voyages.
One of the next projects for the developers is to expand on the new technology’s applications and scale them up for manufacturing and industry. The team—ARS and UCB—has already applied for a joint patent for applying their new method to food preservation, a wise decision considering estimates, according to their study, that “the global frozen food market will reach $404.8 billion by 2027.”
As the world’s population continues to grow, finding better ways to preserve food is essential for achieving global food quality, nutrition and security, as well as energy-efficiency. If the researchers’ concept is successfully tested, scaled up and adopted, it could be a game-changer for global food preservation.
*The Earth & I Editorial Team