Sun. Sep 25th, 2022
Brewing Kombucha Tea.  Note the distinctive gel-like layer of SCOBY (symbiotic culture of bacteria and yeast).
enlarge Brewing Kombucha Tea. Note the distinctive gel-like layer of SCOBY (symbiotic culture of bacteria and yeast).

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Kombucha tea is all the rage these days as a convenient alternative to alcoholic beverages and for its purported health benefits. The chemistry behind this popular fermented drink is also inspiring scientists from MIT and Imperial College London to create new kinds of tough “living materials” that could one day be used as biosensors, help purify water or detect damage to “smart” ones. packaging materials, according to a recent article published in Nature Materials.

You only need three basic ingredients to make kombucha. Simply combine tea and sugar with a kombucha culture known as a SCOBY (symbiotic culture of bacteria and yeast), also known as the “mother,” also known as a tea mushroom, tea mushroom, or a Manchurian mushroom. (Combucha tea is believed to have originated in Manchuria, China, or possibly Russia.) It’s actually related to a sourdough starter. A SCOBY is a firm, gel-like collection of cellulose fibers (biofilm), thanks to the active bacteria in the culture that provide the perfect breeding ground for the yeast and bacteria to thrive. Dissolve the sugar in non-chlorinated boiling water, steep some tea leaves of your choice in the hot sugar water before throwing them away.

Once the tea has cooled, add the SCOBY and pour into a sterilized cup or jar. Then cover the beaker or jar with paper towels or cheesecloth to keep out insects, let it sit for two to three weeks, and voila! You have your own home brewed kombucha. A new “daughter” SCOBY will float right on top of the liquid (technically known in this form as a pellicle). But be warned: it’s important to avoid contamination during preparation, as drinking tainted kombucha can have serious, even fatal, adverse effects. And despite claims that drinking kombucha tea can treat aging, arthritis, cancer, constipation, diabetes or even AIDS, to date there is no solid scientific evidence to support those claims.

Two types of fermentation take place: alcoholic fermentation and acetic acid fermentation, and a really good kombucha will strike the perfect balance between the two. The yeast in the SCOBY produces an enzyme (invertase) that breaks down the sugar into fructose and glucose. The glucose is then broken down into pyruvate, acetaldehyde and finally ethanol, releasing carbon dioxide as a by-product to give kombucha that pleasant whiff of carbonation.

It’s not a lot of ethanol, as the bacteria in the SCOBY convert a lot of it into acetic acid. Too much alcohol would even stop the fermentation process. So most kombucha teas contain less alcohol than even a very light beer. (You can get higher alcohol concentrations if you add too much sugar and/or let the stuff ferment too long, but your kombucha will probably just taste like pure vinegar.)

In addition to its popularity as a drink, kombucha holds great promise as a useful biomaterial. In 2016, for example, Young-A Lee, a professor of apparel, merchandising and design at Iowa State, drew attention for her proof-of-concept research into using dried SCOBY as a sustainable leather substitute. She thought it would be possible to make biodegradable SCOBY-based clothing, shoes or handbags.

There are still a few hurdles to overcome to make SCOBY a viable alternative, most notably how the material reacts to moisture in the air (it softens) and cold temperatures (it becomes brittle). It also takes three to four weeks to grow SCOBY in the lab, then dry and treat it to get that leathery consistency, which is not conducive to mass production. Nevertheless, Lee thought the material showed promise and even made a prototype vest and shoes from the cellulose fiber.

This latest study builds on previous work by MIT engineer Timothy Lu, who E coli to create biofilms embedded with gold nanowires. Those films weren’t quite viable for large-scale applications, so he teamed up with colleagues from MIT and Imperial College London to devise a method to generate harder materials using microbes. Kombucha was a natural choice.

lu et al† couldn’t use the wild yeasts typically used in kombucha because they are genetically difficult to modify. They instead used lab-grown yeast, specifically a species called Saccharomyces cerevisiaewhich they then combined with a bacterium called Komagataeibacter rhaeticus (which can make a lot of cellulose) to make their “mother” SCOBY. (They call it a “Syn-SCOBY.”) They were able to manipulate the cells in the yeast to produce, say, glow-in-the-dark enzymes, or enzymes that could detect pollutants and then release them after detection. to break down. For example, one of their prototype materials detects the pollutant estradiol, while another can detect luciferase, a bioluminescent protein.

Any number of other strains can be exchanged to achieve different functional properties. The authors state that their research has provided a fast, simple method for generating biosensor materials with broad applications. It only took a few days for their “living material” to grow, and they found that over extended periods of time it could grow enough to become the size of a bathtub – at least a thousand times more material than achieved with E coliaccording to co-author Tzu-Chieh Tang, a graduate student in Lu’s lab.

In fact, the researchers also showed that they could grow these living materials in sugary tea, with the possibility that people could one day grow their own water filters at home, for example. “We envision a future where diverse materials can be grown at home or in local production facilities, using biology rather than resource-intensive centralized production,” Lu said.

Organisms are remarkable material-producing systems capable of self-assembling complex materials with diverse chemical and physical properties, starting only from simple raw materials, the authors concluded. “Synthetic material systems that can mimic all of these behaviors do not exist. … The ability to genetically control the process of material self-assembly seen in natural biological materials could revolutionize[ize] the manufacture of products for use in many areas of human life and society.”

DOI: Nature Materials, 2021. 10.1038/s41563-020-00857-5 (About DOIs).

What is kombucha? And are there limits to what we can turn into kombucha?

By akfire1

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