Metabolism 101: Food and Anaerobic Respiration

I’m not sure how humans began using microbes (bacteria and fungi) in food production but it was well before we even knew what microbes are. Nevertheless, microbes are useful because they can undergo a process called fermentation. This process is similar to human anaerobic respiration but produces different end-products.

See, microbes are different from us and can actually thrive in anaerobic or oxygen lacking environments. Bacteria are quite simple and unlike our cells lack key components necessary for aerobic respiration. Therefore, they undergo fermentation which results in the production of byproducts such as ethanol (alcohol), carbon dioxide, or lactic acid. Although simply byproducts for the bacteria, humans taken advantage of them to make food.

So what are some of these commonly used microbes?

Saccharomyces cereviceae is a common strain of yeast. These little guys have been used everywhere from my old lab to wine, beer, and bread making. They convert sugars present in foods into ethanol and carbon dioxide. These sugars range from maltose in barley for beer, glucose and fructose in grapes for wine, or starch in wheat for bread. The alcohol gives beverages its distinct properties while the carbon dioxide helps develop taste and fizziness.  In terms of bread, the carbon dioxide makes the dough rise while ethanol evaporates during the baking process.

In the milk industry the well known probioticsLactobacillus bulgaricus and Streprococcus thermophilus, are commonly used. These little guys convert the milk sugar, lactose, into lactic acid, thus giving the final product that acidic taste. At the same time the acidity will alter the milk protein structure which gives yogurt its thick texture. The beauty of Lactobacillus is that it’s not necessary to use milk in order to culture them. Anything that’s got a sugar will do the job! That is the reason why you can make all of these non-dairy yogurts. All the benefits of probiotics without all the nasty saturated fat 😉

Lastly I wanted to mentioned kombucha which is fermented tea. In this case the fermentation involves SCOBY or symbiotic culture of bacteria and yeast. The exact composition of the culture varies but generally consists of Acetobacter sp. along with various yeasts such as Bretanomyces sp. and Saccharomyces sp. All in all, the sugar in the tea will feed the culture which will give off useful bi-products such as a bit of alcohol, acetic acid and gluconic acid. The gluconic acid is key for kombucha and is believed (although not well researched) to have liver cleansing properties.

La voila! Here are some of the common microbes we use in our food.

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