Open the freezer door and there, method within the again, could also be an outdated carton of ice cream rising spikes of ice. Or a forgotten frozen lasagna lined in icy crystals. Or drying of meat surfaces if not nicely lined.
Folks generally name this phenomenon “freezer burn,” and it occurs when tiny ice crystals on the meals’s floor evaporate straight into vapor with out first going by means of the liquid water part – a course of scientifically termed sublimation. This moisture loss can go away the meals’s floor layers dried out and discolored.
As a meals scientist, I name the preliminary floor ice formation “ice recrystallization” and research methods to sluggish it down.
Ice recrystallization damages and destroys natural cells – the smallest dwelling items present in animals and vegetation. It’s simply as a lot an issue when storing harvested meals crops or biomedical analysis supplies – like cell cultures – as it’s for storing frozen pizza or peas, and may result in plenty of waste.
There are synthetic substances that stop this sort of ice injury, however few of them are fit for human consumption. So together with fellow College of Tennessee and Oak Ridge Nationwide Laboratory scientists, I’m working for the following three years below a $550,000 grant from the Nationwide Science Basis to determine protected “bio-based” choices – supplies already present in nature, together with substances derived from the pure human digestion course of when meals is consumed.
How does ice recrystallization occur?
The meals trade makes use of “blast freezing” to keep away from formation of huge ice crystals in frozen meals. This course of entails exposing meals in a short time to a low temperature and a excessive charge of air motion, which causes the meals to freeze right into a mass of quite a few small crystals. Small crystals are a lot much less damaging to frozen matter than giant ones.
The issue begins after these meals are moved to common freezers for storage, together with dwelling freezers. The automated defrost perform in such items entails turning the compressor on and off a number of instances a day, reducing and elevating the temperature to stop ice buildup. This fluctuation partially melts the ice within the meals after which re-freezes it, a course of that will create bigger and extra damaging ice crystals.
These modifications could make meals at finest unpalatable – who hasn’t endured consuming freezer-burned greens or a watery, thawed strawberry? – and at worst unusable.
In keeping with a latest research by School of William & Mary meals system researcher Zach Conrad, complete spending on meals in america per particular person per day, between 2001 and 2016, was $13.27, and $3.62 value of that expenditure, or 27%, was wasted meals.
Conrad discovered that simply 1.4% of that waste concerned frozen meals, amounting to about 5 cents per particular person per day, or $18.25 yearly. However these nickels add as much as greater than $5.89 billion value of frozen meals wasted yearly.
In order the frozen meals market continues to develop, the significance of minimizing or stopping ice injury turns into apparent.
Stopping ice development with synthetic substances
The artificial chemical compounds that stop ice recrystallization are usually poisonous to dwelling organisms, so their usefulness for shielding meals could be very restricted. Through its prolonged and rigorous evaluate course of, the U.S. Meals and Drug Administration has permitted a man-made polymer referred to as polyvinyl alcohol, or PVA, as protected to be used in meals packaging supplies, however not as a meals additive.
PVA is used industrially to stop ice recrystallization in substances like cement and concrete, in addition to when freezing human cells, tissues and organs to protect them for transplantation and biotechnology makes use of.
There are additionally “semi-synthetic” compounds – so labeled as a result of they’re made by altering naturally occurring supplies – that maintain promise for curbing ice injury. They embrace substances referred to as glycopolymers and polyampholytes, which have been reported to inhibit ice recrystallization, protect cells and enhance cell viability. Many of those compounds are in early phases of analysis and improvement, and never but used commercially. Their security to be used in meals has but to be demonstrated or permitted.
A safer various: Bio-based options
I analysis alternate options to each artificial and semi-synthetic supplies which are bio-based – that’s, primarily based on substances already present in people, animals and vegetation, and thru pure organic processes. I imagine that these bio-based options are particularly promising choices as a result of they don’t contain unnatural manipulation.
DigitalVision by way of Getty Photographs
As an illustration, for the egg processing trade, I found the best way to use pure peptides derived from eggs – quick strings of amino acids additionally present in our guts – to stop freezing-caused injury to egg yolks, moderately than including salt or sugar to yolk earlier than freezing.
Below our Nationwide Science Basis grant, my workforce is researching substances that mimic the capabilities of the antifreeze proteins present in cold-water fish or cold-tolerant vegetation, which inhibit ice recrystallization and stop ice development of their inner tissues.
One problem is that these antifreeze protein molecules are current in very low concentrations in nature. This makes them very expensive to extract from organisms and produce them at an industrial scale.
We’re conducting analysis on peptides derived from each widespread and distinctive meals proteins, resembling soybeans, dairy, fish, meat and bugs. Because of analysis by Srinivasan Damodaran of the College of Wisconsin, we already know that small peptides from fish gelatin and cattle collagen proteins are efficient in stopping ice recrystallization in ice cream. This energy of peptides varies significantly relying on the supply protein, nonetheless, so we’re investigating the explanations for these variations.
As we be taught extra about these peptides and the best way to produce them at a industrial scale, I imagine they could be helpful throughout a number of industries, from bettering the standard of frozen meals, to rising the resistance of agricultural crops to freezing temperatures, to higher preserving cells and tissues, and even in makes use of like de-icing roads and plane.
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