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  • Alex Cloherty

Munchy munchy microbes

Updated: Dec 8, 2021

Here in the Netherlands, food waste is a big topic in certain circles. The app "Too Good To Go", which notifies you of locations where you can pick up packages of food that is either leftover or near its expiry date - from cafes or grocery stores or bakeries for example - is a real hit amongst students. Probably that is due to both its left-leaning ideology, and the fact that that food is sold at a highly reduced price. In Amsterdam and Utrecht, you will also find an organization with the catchy name, "Taste Before You Waste". Their goal? To reduce food waste, on a local scale and with a bottom-up approach, by, for example, cooking community dinners made out of salvaged food.

It's not only in the Netherlands that food waste is an important topic. According to the Food and Agriculture Organization, a mind-boggling 30% of our annual food production is never eaten, and goes to waste. A full third of all the food that we produce is going to landfill! Not only is this concerning in regards to equity in food access across human populations, but this loss also poses environmental concerns. Oftentimes the waste food does indeed go either to a landfill, or it is incinerated - turning gold into lead if you will. Not only is this food destroyed, but this type of disposal can lead to downstream water, soil, and air pollution.

But never fear. As you may have guessed, the microbes are here!

Well, ok, maybe fear a little bit. This is still a big issue for humanity to tackle in order to equitably feed a growing global population. But to throw some good news into the mix, today I want to tell you about how scientists are learning to harness the power of bacteria and fungi to turn that food waste into valuable secondary products. Scientists are figuring out how to restore that lead into gold.

Food waste is a particularly interesting type of waste because it is naturally so nutritious. It has loads of biologically useful ingredients, like sugars, proteins, starch, micronutrients, bioactive compounds, and dietary fibers. Those components are not only good for you and me, but also for our little microbial buddies. But instead of just producing a smelly stool at the end of their digestion process, when certain microbes eat up these ingredients they can produce poop in the form of biofuel, biodegradable plastics, fertilizers, and even electricity.

Single celled fungi are a great example for this concept. For instance, scientists were able to use Saccharomyces cerevisiae, the same kind of yeast that we use to leaven bread, to turn instant noodle waste into bioethanol. This yeast is able to eat up the starch in the noodle waste, and ferment that starch to produce bioethanol - in much the same way that the yeast in beer eats up the sugars in wort to produce that ever so tasty drink. Yeasts are experts in eating sugars, extracting energy, and pooping out carbon dioxide, ethanol, and a mix of acids.

How does this work? Well, these products of yeasts' digestion are made of carbon, hydrogen, and oxygen, just like the input sugars. However, the output from the yeast is composed of less structurally complex and energetic molecules than the input sweet stuff. As a very (very) rough rule of thumb, the more complex molecules are, the more energy it takes to make them. By breaking down complex sugars and leaving behind simpler molecules, yeasts squeeze out the chemical energy that was holding those sugars together, and then use that energy to power themselves.

So to summarize, yeasts absolutely love to be used in fermentation. When we humans want to make beer or biofuels, all we have to do is feed the yeast a feast and they'll do all the work for us - given that we keep them at the right temperature and pH, that is. I mean, you also wouldn't enjoy a feast as much if you had to eat it in a 50 degree vat of acid, right?

But back to the noodles. Researchers were indeed able to feed yeast, S. cerevisiae, instant noodle leftovers, and get bioethanol out. They even achieved an ethanol conversion rate of up to almost 97% - meaning the yeast made short work of those noodles and very little biological material went to waste.

To add to the coolness of this situation, the researchers even used the waste products of the waste products. After realizing that the yeast prefered their noodles sans oil, the researchers started boiling the oil off of the noodle waste to provide their Saccharomyces solely sugar. But then that waste oil from the waste noodles was even put to use! The researchers added a mix of chemicals (potassium hydroxide, also known as lye, and sulphuric acid, for the chemistry nerds out there) to the leftover oil to make biodiesel! They were able to convert up to nearly 99% of the waste oil into biodiesel within only a few hours. Talk about zero waste. As a fun fact, similar strategies have also been used to produce bioethanol from waste pizzas or hamburgers, with production yield of 0.292 grams ethanol per gram of waste pizza, or 0.271 grams ethanol per gram waste hamburger.

Of course, feeding our wasted food to microbes is not a solution on its own. A complete solution for eliminating food waste would also have to include a systems-based approach in which we would try to prevent so much waste from happening in the first place. But nonetheless, using microbes to turn our trash into treasure is one exciting tile in a mosaiced solution.

Until next time - eat up!

~ Alex

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