A fresh baked loaf of sourdough bread, a yogurt parfait, some kimchi and rice - all of these delicious foods have something in common. Aside from being delicious, they’re alive! Fermented foods like these ones contain live cultures, sometimes called probiotics, that can help digestion and boost immunity. Tara Parker-Pope at The New York Times gives the “Do’s and Don’ts” of eating and shopping for fermented foods; this article will summarize her findings, and provide some of the chemistry to go along with it.
Parker-Pope explains that yogurt, kimchi, and sauerkraut, kombucha, and kefir are fermented foods that promote good digestion and immunity. Other foods to look out for at the store include miso, cottage cheese, gouda cheese, and some apple cider vinegar. Parker-Pope explains that not all fermented foods are created the same. The consumer should be looking for a label that says “live cultures,” “contains probiotics,” or “naturally fermented,” in order to receive the benefits of these foods, as manufacturers sometimes remove the probiotics from the foods before they are packaged and hit the market. It is also possible to make many of these foods at home. Online recipes are available and even can be found through The Times website. You can receive the same benefits from these health foods right from your kitchen.
These cultures are actually a variety of microorganisms. They come in the form of bacteria, yeast, and mold - all of them capable of the fermentation process. Fermentation occurs when these superbugs break down glucose into lactic acid, or ethanol and carbon dioxide. Which process occurs depends on the organism and the resources available to them. Both processes are outlined below. In alcoholic fermentation, glucose (sugar) is broken down into ethanol (alcohol) and carbon dioxide. In lactic acid fermentation, glucose is broken down into two lactic acid molecules.
C6H12O6 (glucose) → 2 C2H5OH (ethanol) + 2 CO2 (carbon dioxide)
C6H12O6 (glucose) → 2 CH3CHOHCOOH (lactic acid)
In her article, Parker-Pope keeps to a recent study where yogurt, kimchi, sauerkraut, kombucha, and kefir are the focus. Of these, yogurt, kimchi, sauerkraut, and kefir - a fermented milk drink, all are created via lactic acid fermentation. Kombucha is made by microorganisms that produce ethanol.
Both processes start with a familiar biochemical pathway, glycolysis. In glycolysis, glucose is broken down into two molecules of pyruvate. This involves a number of enzymes that split the glucose molecule into two, and alter the halves in small steps, sort of like an assembly line. The overall reaction is shown below.
After glycolysis, NADH needs to be regenerated as NAD+. Producing lactic acid or ethanol accomplishes this task. In this first instance, acetaldehyde, a commonly occurring biological molecule, acts as an intermediate between pyruvate and ethanol. The conversion of acetaldehyde to ethanol achieves the conversion of NADH back to NAD+.
Lactate dehydrogenase accomplishes this task similarly in lactic acid fermentation.
After looking into the biochemistry of fermentation, it is clear that fermentation is a pretty complex process, but the good impact fermentation has on our foods is a little more straightforward. Probiotics in food outcompete harmful bacteria and produce beneficial nutrients for the body, resulting in overall better health.
References
Duke, O., Gloyd, J., Meluskey, J., Peralta, J., & Velazquez, F. A. (n.d.). Group 4 Midterm.
Khan Academy. (n.d.). Fermentation and anaerobic respiration | cellular respiration (article). Khan Academy. https://www.khanacademy.org/science/ap-biology/cellular-energetics/cellular-respiration-ap/a/fermentation-and-anaerobic-respiration.
Lactate Fermentation : Anaerobic fate of Pyruvate. (2020). Youtube. https://www.youtube.com/watch?v=EnX9YzoUOo8.
Parker-pope, T. (2021, August 19). The DOS and don'ts of fermented foods. The New York Times. https://www.nytimes.com/article/fermented-foods-dos-facts.html?.%3Fmc=aud_dev&ad-keywords=auddevgate&gclid=Cj0KCQjwssyJBhDXARIsAK98ITQSNarxR8kydsZxs2pyYLXWgz413EF8ZauNiAci2iTeNdeLIRBY5NYaAnVpEALw_wcB&gclsrc=aw.ds.
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