Open the freezer door, and there, at the back, maybe an old box of ice cream with points of ice. Or a forgotten frozen lasagna covered in ice crystals. Or drying the meat surfaces if they are not well covered.
People sometimes call this phenomenon “freezer burn”. It happens when tiny ice crystals on the surface of food evaporate directly into vapor without first going through the liquid water phase – a process scientifically called sublimation. This moisture loss can leave the top layers of food dry and discolored.
As a food scientist, I call the initial formation of surface ice “recrystallization of ice” and study ways to slow it down.
Recrystallization from ice damages and destroys organic cells, the smallest living units found in animals and plants. This is just as much of a problem when storing harvested food crops or biomedical research equipment – like cell cultures – as it is when storing frozen pizzas or peas and can lead to a lot of waste.
There are man-made substances that prevent this kind of damage from ice, but few of them are safe to consume. So, along with other scientists at the University of Tennessee and the Oak Ridge National Laboratory, I am working for the next three years with a $ 550,000 grant from the National Science Foundation to identify “bio-based” options. safe – materials already found in nature, including substances derived from the natural process of human digestion during the consumption of food.
How does freezer burn occur?
The food industry uses “quick freeze” to prevent large ice crystals in frozen foods. This process involves exposing the food to a low temperature and high air flow very quickly, causing the food to freeze into a mass of many small crystals. Small crystals are much less damaging to frozen material than large ones.
The problem begins after these foods are transferred to regular freezers for storage, including home freezers. The automatic defrost function of these units is to turn the compressor on and off several times a day, lowering and raising the temperature to prevent ice build-up. This fluctuation partially melts the ice in food and then refreezes it, a process that can create larger and more damaging ice crystals.
These changes can make food unpleasant at best – who hasn’t endured eating freezer-burnt veggies or a watery, thawed strawberry? – and at worst unusable.
According to a recent study by Zach Conrad, a food system researcher at the College of William & Mary, the total food expenditure in the United States per person per day, between 2001 and 2016, was $ 13.27, and $ 3.62 of those expenses, or 27 percent, were food wasted.
Conrad found that only 1.4 percent of that waste was from frozen food, which works out to about 5 cents per person per day, or $ 18.25 per year. But those pennies add up to more than $ 5.89 billion in frozen food wasted each year.
As the frozen food market continues to grow, the importance of minimizing or preventing damage from ice becomes evident.
Prevent ice formation with artificial substances
Synthetic chemicals that prevent recrystallization in ice tend to be toxic to living organisms, so their usefulness in protecting food is very limited. Through its long and rigorous review process, the United States Food and Drug Administration has approved an artificial polymer called polyvinyl alcohol, or PVA, as safe for use in food packaging materials, but not as a food additive. .
PVA is used industrially to prevent recrystallization of ice in substances such as cement and concrete, as well as in the freezing of human cells, tissues and organs to preserve them for transplantation and biotechnology. .
There are also “semi-synthetic” compounds – so labeled because they’re made by modifying natural materials – that show promise in reducing ice damage. They include substances called glycopolymers and polyampholytes, which inhibit recrystallization from ice, preserve cells, and increase cell viability.
Many of these compounds are in the early stages of research and development and have not yet been used commercially. Their safety for use in food has not yet been demonstrated or approved.
A safer alternative: bio-based solutions for freezer burn
I am looking for alternatives to synthetic and semi-synthetic materials that are bio-based, i.e. based on substances already present in humans, animals and plants, and through natural biological processes. I think these bio-based solutions are particularly promising options because they do not involve unnatural manipulation.
For example, for the egg processing industry, I discovered how to use natural peptides derived from eggs – short chains of amino acids also found in our intestines – to prevent freezing damage to egg yolks. eggs, rather than adding salt or sugar to the yolk. before freezing.
As part of our National Science Foundation grant, my team is researching substances that mimic the functions of antifreeze proteins found in cold-water fish or cold-tolerant plants, which inhibit ice recrystallization and prevent growth. ice in their internal tissues.
One challenge is that these antifreeze protein molecules are present in deficient concentrations in nature. This makes them very expensive to extract from organisms and produce them on an industrial scale.
We are conducting research on peptides derived from common and unique dietary proteins, such as soy, dairy, fish, meat and insects. Thanks to the research of Srinivasan Damodaran at the University of Wisconsin, we already know that the small peptides in fish gelatin and collagen proteins from cattle are effective in preventing ice recrystallization in ice cream. However, this potency of peptides varies greatly depending on the source protein, so we are investigating the reasons for these differences.
As we learn more about these peptides and how to produce them on a commercial scale, I believe they can be useful in several areas, from improving the quality of frozen foods to increasing the resistance of agricultural crops to freezing temperatures, through better preservation of cells and tissues, and even in uses such as de-icing roads and airplanes.
This article was originally published on The conversation through Tong (Toni) Wang To University of Tennessee. Read it original article here.