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Newly developed antioxidant mats containing tannic acid derived from red wine could limit spoilage in foodstuffs by reducing oxidation.
Oxidation is the culprit behind many examples of food spoilage and wine connoisseurs will be painfully familiar with the dangers of wine becoming oxidized. Antioxidants can combat these spoilage effects by curtailing oxidation, but their ability to do this is severely limited and unfortunately does not last very long.
In a new paper published in the journal ACS Applied Material & Interfaces, researchers from Texas A&M have revealed a crafty mechanism that builds upon the properties of certain antioxidants to combat food spoilage. The team has created mesh-like mats composed of a network of intertwined ultra-fine polymer and antioxidants from red wine contained within tannic acid.
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The mats in question are strong and stable, making them capable of delivering antioxidant effects for an extended period of time. But, even though the problem of food spoilage should not be underestimated, the mats could have another, more pressing usage. When worked into bandages, the research team says that the antioxidant mats can help prevent the build-up of free radicals, promoting healing of the affected area.
The paper describes the team’s perfection of a system to spin defect-free nanofibers into mats capable of delivering high-performance antioxidant effects. The key to this breakthrough is the fact that they have been able to molecularly bind several antioxidant molecules to each nanofiber.
This means the final mat which constructed of millions of such fibers has massively enhanced antioxidant capability.
This is not the first time that antioxidants have been put forward to combat food spoilage. Kemin Industries is just one of many commercial ventures that offer products that utilize antioxidants as a solution to oxidation. The manufacturer uses both novel synthetic antioxidants, and natural antioxidants found in rosemary and green tea to halt the cycle by which oxidation spoils food to significantly increase the shelf life of foodstuffs.
Even so, the use of a mat that does not add any unnecessary ingredients and additives is highly desirable, especially when it comes to wine production.
Tackling Food Spoilage
Food deterioration during storage is a primary concern for the food industry, as well as a major environmental issue, and oxidation — in addition to bacteria contamination — is one of its major causes.
Oxidation occurs when oxygen is able to reach fats, pigments, or cells of foodstuff. The most common example that everyone is likely familiar with, is a damaged apple becoming ‘bruised.’ The development of a darker hue around the damaged area is a result of oxygen making contact with cells within the apple. A much less pleasant example is when oxygen reaches fats in meats, this results again in a darkening effect, but when left can lead to foul smells, odors and sour tastes.
Yet oxidization is a problem that is most familiar to winemakers and consumers. In alcoholic drinks such as wines, excess oxidation leads to the formation of acetaldehyde. This alters the drink’s taste, color, and smell.
So far, the tools at the disposal of winemakers have been fairly limited. One technique used is the limiting of contact with oxygen immediately after fermentation, with careful use of vacuum-sealed containers used during barreling and bottling. Mitigating all contact with oxygen is impossible.
Winemakers can also add sulfur dioxide to their wine to grab free radicals and reduce oxidation. The major problem with this technique is that if used liberally the chemical can mask some of the wine’s more delicate aromas and tastes.
Antioxidants control oxidative reactions by combining with ambient oxygen, or alternatively, by donating electrons to ‘free radicals’ to neutralize them. Free radicals are atoms with unpaired electrons, which cause damage in foodstuffs and in the body as they tend to be extremely chemically reactive, snatching electrons to complete pairings. Having a substance that can ‘scavenge’ these free radicals and freely donate electrons to them can limit the cellular damage they cause.
In particular, research has found that tannic acid— a compound found predominantly in red wine — is of particular use as an antioxidant in food storage because it also has limited antibacterial qualities. These properties arise as a result of the presence of atom groups called polyphenols in the molecular structure of tannic acid. The sheer abundance of these polyphenols makes tannic acids an excellent scavenger of free radicals.
Of course, this leads to the natural question, if tannic acids and by extension, polyphenols are so beneficial in preventing spoilage, why are they not being used more widely already?
It turns out that in previous studies, the synthetic mats that material scientists have created have been flattened into sheets. As a result, the surface area across which the antioxidants can act is severely limited.
One of the team’s main objectives was to increase the surface area for antioxidant action. They tackled this by using a new blending technique and a polymer capable of gripping multiple tannic acid molecules via hydrogen bonds, resulting in a mesh of ultrafine fibers and tannic acid, each strand of which makes its own contribution to antioxidant activity.
The beauty of using a hydrogen bond to attach the tannic acid molecules to the fibers — made from a material known as polyvinylpyrrolidone — is that it increases the strength of the mats by a factor of 10 when compared with mats comprised of polyvinylpyrrolidone alone. Additionally, the use of hydrogen bonds means that the flow of tannic acid from the mat can be controlled by changing the pH of the substrate in which the mat sits.
A lack of defects in the mats, confirmed under an electron microscope, also increases this tensile strength, as well as giving them admirable stability in water.
All this results in an antioxidant mat which has impressive tensile strength whilst still being flexible enough to be described as cloth-like, and stable enough to deliver sustained and controllable antioxidant activity for a period of around 20 days. Thus, the mats can be used for the inner-linings of food containers and in bandages, preventing cellular damage from free radicals that can hinder the healing process.
We can be thankful that the researchers from Texas A&M never listened to the adage that solutions cannot be found at the bottom of a bottle, because in the case of spoilage through oxidation the answer may have lurked in wine bottles all along.
References and Further Reading
Gaikwad, A., Hlusko, H., Karimineghlani, P., et al. . ‘Hydrogen-Bonded, Mechanically Strong Nanofibers with Tunable Antioxidant Activity,’ ACS Applied Material & Interfaces,[https://pubs.acs.org/doi/10.1021/acsami.9b23212]
Brewer. S,  ‘What is oxidation, and how does it alter food products?’