Homestead Science: How Does Lactic Acid Fermentation Work?

In this post, we are going to look at one type of fermentation that humans use to process food in a healthful way. If you need a brief primer on the basics of fermentation in general and why these microorganisms ferment food for us, then read the first article in the series found here. (https://steemit.com/fermentation/@slhomestead/homestead-science-the-basics-of-fermentation )

Two important lessons from The Science of Fermentation part 1 are that organisms require food in order to get nutrients and energy to live and that they ferment food in order to unlock that energy. Today, I will answer your next burning question: "How does lacto fermentation work?"

In General Terms
Fermentation, regardless of the specific type, takes sugar molecules found in food and breaks them in half. This cleaving of sugar molecules releases a tiny bit of energy that can be used by the cell to perform various vital functions. It is the next step in fermentation that varies from one type to another. In lactic acid fermentation, that half of a sugar molecule is changed into lactic acid, which is where we get the name of this sort of fermentation. The reason lactic acid is formed is to allow the chemical reactions to continue and release more energy from other sugar molecules.

A Bit Deeper
Hold onto your seats, folks. I am going to go all science on ya. When I taught about fermentation in school, I would split it up into two parts. The first part of fermentation where glucose (and other sugar molecules) is broken into two identical molecules called pyruvate is known as glycolysis. This fancy science word literally means “sugar cut” because that is exactly what is happening. However, it is crucial to know that glucose doesn’t just randomly break in half. There are actually over 10 other chemicals (called enzymes) that help this happen. But even if you had glucose and these other enzymes, it still wouldn’t work. You need two other chemicals; one is called NAD+ and the other is called ADP.

Now, if you are a really astute observer, then you might recognize ADP as looking a whole lot like ATP (which we discussed in our first article). And you would be correct! You can look at ADP and ATP as the same molecule. When it is “charged up” with energy, it is called ATP, and when it is drained of that energy, it is called ADP. So, ADP is going to take some of the energy found in the glucose and become ATP. In a similar fashion, NAD+ and NADH are pretty much the same molecules. When NAD+ takes an electron from the glucose molecule, it becomes NADH; if it hands that electron to something else, it goes back to being NAD+.

Okay, so now the stage is set for the second part of the fermentation process. The most important thing to remember at this point is that there is only a certain amount of NAD+/NADH and ADP/ATP in each cell. So, eventually, once all of the ADP becomes ATP and all of the NAD+ becomes NADH, the chemical reaction would come to a screeching halt even if you had lots of sugar around. So, something has to take the energy from ATP (to make it back to ADP) and the electron from NADH (to make it back to NAD+). Normal cell functions use the energy from ATP, so that is not an issue. Usually, the issue is getting NADH back to NAD+. In lactic acid fermentation, pyruvate is what does that—pyruvate will take the electron back from NADH. NADH will become NAD+ and pyruvate will become lactic acid. Now the cell can allow glycolysis to continue and get more energy!

Where Does This Occur?
Lactic acid fermentation occurs all over the world in myriad places, but you actually don’t even need to look outside of your own body in order to find it occurring! When we go through a period of intense exercise, our body uses this method of fermentation in order to give us quick energy. However, it does have a notable side effect! All of that lactic acid building up in our muscles causes them to burn—something that everyone has experienced at one point or another.

You could probably guess many of the other products produced through lactic acid fermentation. Just think of things that have a sourness to them, as that is how our taste buds interpret acid in our foods. Sour cream, yogurt, kefir, various cheeses, pickles, sauerkraut, kimchi, and so much more! These are all produced through the efforts of lactic acid bacteria (and other microorganisms).

Benefits of Lactic Acid Fermentation
If you are on this website, you probably don’t need to be told that fermenting foods is good for you, but I will tell you that anyway. And many scientists would agree with me. Stanley Gilliland found that the benefits of lactic acid fermentation include: increasing nutrient availability in food, controlling some forms of cancer (especially those of the digestive system), and keeping intestinal infections in check. You can read all about his findings here (http://www.sciencedirect.com/science/article/pii/037810979090705U ). Lactic acid fermentation has also been shown to help with allergies (see here http://www.sciencedirect.com/science/article/pii/S156757690100025X ), improve food safety (see here http://www.sciencedirect.com/science/article/pii/S0956713597000753 ), and lengthen the shelf life of food (see here http://www.sciencedirect.com/science/article/pii/S0956713597000157 ). I could go on, but this probably deserves a blog post or two in its own right!

In summary, eat more fermented foods!

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This is the second in a series of posts we'll be putting up on how the different types of fermentation work. Andrew first wrote this article for the Fermentools.com blog that we contribute to (can you tell he used to be a science teacher?). Check out the original article in its context here! http://www.fermentools.com/blog/how-does-lactic-acid-fermentation-work/

If any of you homeschooling parents want more information or ideas on how to share this information with your kids, please don't hesitate to ask!

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