I haven't posted here in a while. I'm going to try posting something blank and building it up over time, like a wiki article. It surely won't ever get posted if I write it in a text editor. So here we go: Space Food. Part 2/3.
Microbial manufacturing:
Food molecules in nature are made through molecular assembly by enzymes. Let's do that. Our nanotech isn't far enough, but our bio tech is. One option is that we can grow microorganisms and remove their enzymes with a centrifuge, allowing us to do their chemistry ourselves at larger scales. Homebrewers buy amylase for example to break down starches into simpler sugars. Enzymes extracted from yeast (twelve of them and some nucleotide cofactors, collectively known as zymase) are then capable of fermenting sugars! Without cells! This fact basically led scientists in the early 1900s to discover the reaction pathways of glycolysis and fermentation, in a very exciting sequence of Nobel prize-winning discoveries that also involved enzymes extracted from animal muscles. Muscle enzymes, you see, serendipity of serendipities, also perform fermentation, and that let us work at characterizing the chemistry from two different angles. It was basically like two dogs eating one strand of spaghetti and then kissing in the middle, but for scientists researching carbohydrate metabolism. So yeah, we can do a lot of cool digestive chemistry in a cell-free environment. And that was a hundred years ago! We can do a lot more these days.
Another option for microbial manufacture of food is to let the microbes do it and not kill them with a centrifuge. Let's talk about single-cell proteins, SCPs! There are four main ones. Spirulina, chlorella, yeast, and quorn. They're all reportedly complete proteins: each cell contains some of the nine proteinogenic amino acids that humans can't synthesize. I plan to investigate their content of conditionally essential amino acids too. And their vitamin content. And their fatty acid content. I'm curious if there's a mix of the four big SCPs that lets you meet daily dietary recommendations if you eat, say, 300 grams of SCP per day. What's a good ratio of spirulina to quorn? But let's talk about them one at a time first, and get to the joint optimization later.
Spirulina is an aquatic photosynthetic cyanobacterium (genus Arthrospira), and like all cyanobacteria, it's a prokaryote - it's a super simple cell with no organelles. And it's so fucking cool. I could talk about it all day. The rest of this big paragraph is just going to be about the history of where it grows, not even about the organism as a food source. That's how cool it is. The Aztecs used to harvest it (Arthrospira maxima) from the alkaline Lake Texcoco that surrounded their islet city of Tenochtitlan. They called it "rock excrement", tecuitlatl. The other lakes of the Valley of Mexico aren't as alkaline, and the Aztecs had dams to keep the lakes from mixing in times of flooding. Unfortunately, the dams were destroyed in Cortes's siege of Tenochtitlan in 1521, and the culture that harvested spirulina was destroyed soon after. Soon Texcoco was drained to make arable land, and to mine its sodium carbonate, and five hundred years later, the whole of Mexico City is still an ecological disaster. A bunch of local species of fauna are critically endangered or recently extinct, including the Cozumel Thrasher bird and the axolotl, an adorable and fascinating salamander. Also, the city is all at once sinking, flooding, and running out of drinking water. I shake my damn head. Okay, back to spirulina. Back in the 1960s, the Mexican people started harvesting spirulina again! A company called Sosa Texcoco had a huge concrete solar evaporator for getting soda from what remained of the Texcoco lake bed, and spirulina was fouling their machinery, so they tried growing it for food. It worked for a while. Then they went out of business. At the same time that spirulina was rediscovered in Mexico, Science and Western civilization were discovering spirulina in Africa. The Kanembu people of Chad were harvesting spirulina (Arthrospira platensis) on the shores of Lake Chad, where they call it dihe. And spirulina also grows in the alkaline lakes of the African Great Rift Valley, where it's the preferred food of the Lesser flamingo! Imagine, if you will, a festive holiday meal celebrated over a traditional roasted Martian flamingo. And there's a family of pet axolotls smiling from an aquarium. Spirulina also grows in Lonar Lake in India, a high-velocity asteroid impact crater! And it grows in Chenghai lake in China, and two lakes in Myanmar. And I'm sure those places have good stories too. I think it's even been found in merely saline waters of lower pH, like the coastal lagoons of Del Mar, California, by San Diego. I got my live culture from a company there. But it usually grows in high pH water, which keeps down populations of basically everything else - all the microorganisms that aren't alkaliphilic. That's super convenient for growing it as a food source. And there are other cool things about the organism itself, and not just where it grows, like how it changes shape to shade itself when there's too much UV radiation.
Next time I'll talk about spirulina as food, along with chlorella, yeast, and quorn, and the ease and difficulty and merits of growing them. Vitamin concentrations, purine metabolism, taste, ethyl carbamate production, stuff like that.
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Chlorella:
Yeast: Yeasts are unicellular fungi. The one used in brewing and baking, Saccharomyces cerevisiae, can be eaten in bulk as a single-cell protein. In bulk, it's usually consumed as marmite or yeast flakes. Marmite is also called yeast extract or yeast hydrolysate, and it's a paste made by heating the cells so that they burst, and then filtering out the ruptured cell walls, which have lots of indigestible beta-glucan polysaccharides. You can also mill the yeast and dry it out, to get nutritional yeast powder, which is called "nooch" if you're being cute, although some abbreviation of "yeast flakes" would have been a lot more descriptive. On earth, nutritional yeast is fortified with laboratory vitamins to appeal to vegetarians, which makes looking up its vitamin content a little harder, but I know that yeast naturally contains vitamin D pro-vitamer called ergosterol, just like chlorella, and that it does not contain B12, since it's not a bacterium. Lots of websites call yeast flakes a complete protein, but no one gives the amino acid profile (e.g.. in mg acid per gram of substance). Also, no one calls marmite a complete protein, which is pretty suspicious. You'd think that if it were a good protein source, then someone would be advertising the fact. The best data I've found so far is a table in "Nutritional Yeast Biomass: Characterization and Application" (p 282 of the pdf, p 255 of the book) that gives a profile for 8 of the 9 essential amino acids, skipping histidine. And what does the table say? ...
Nutritional yeast powder is not great to eat. It is sometimes described as nutty or cheese-like, but these are euphemisms for bitter and funky. Funky as in food spoilage. You'd think it would taste like beer or sourdough bread, but the aroma of a live yeast culture is not the dominant flavor, from what I've eaten. It's also salty, and I don't if that's from the yeast's cellular composition or the food on which it's grown or if it's added later. Nutritional yeast is interesting in small amounts as a seasoning, and if you've had it on popcorn more than once, you might soon come to crave it as a seasoning. But it's difficult to eat in large amounts, both because of the strong flavor and because the dry flakes are hard to transform into a pleasing texture. I've tried mixing it with glucose syrup and with citric acid and with garlic and with other things. Glucose and garlic and oil made it taste remarkably like the crust of a pizza from a fast-food restaurant, which until then I had not realized to be so sweet. Still, you would have to be highly motivated to get say 20% of your daily calories from nutritional yeast powder. Or maybe I just need to invent some better recipes. I made a drink of it with cinnamon and ginger and granulated sugar. I got it down, but the aftertaste was like a dusty barn or some other non-food. What happens if you make a paste of it with water and then toast it like a tortilla or fry it like a fritter? Citric acid was not an improvement, but what about other organic acids or an alkali? Vinegar? Malic acid? I don't think savoriness was the missing factor, but why not try MSG? Or mix it back in with the beer from whence it came. I have some culinary investigating to do. The best way to eat it I've found so far is sadly to eat it dry with carbs, like cereal. Moistening it seems to make the flavor more pronounced. If palatability seems to be a real problem in space, even for highly motivated individuals, that's still not a defeating consideration for nooch as a protein source: you could just pipe it into someone's stomach with a PEG tube through their abdominal wall. The stomach can also be picky about foods, but often less so than the mouth. I don't actually think that will be necessary. People are pretty good at learning to like weird foods, especially if the food is a major source of calories in their diet or if it's simply very salty. I just need a better recipe. Update: nooch and vinegar is pretty good. I can totally imagine astronauts using a nooch based vinaigrette salad dressing to increase their protein intake. Or little nooch meatballs with a brown sugar vinegar glaze maybe. Or nooch hotdogs with a mostly vinegar mustard? Idk.
The other common culinary form of yeast (called yeast extract, or yeast hydrolysate, or marmite) I've not tried, but I understand it's also salty, and strongly flavored, and an acquired taste, and mostly used as a condiment or the base for a soup broth. I look forward to acquiring some, especially if it has a similar nutritional profile and a different taste.
Growth: Yeast is ridiculously easy to grow in nature. It grows by itself on the skin of fruits and on the skin of people. You can leave flour/water paste out in a forest or field and capture wild yeast from the air. But what about feeding it on just chemicals and/or microorganism byproducts, since we haven't gotten to the botanical manufacturing section of this essay yet? Despite its ubiquity in nature, growing yeast on a chemical diet is a little bit tricky, compared to, say, spirulina. Yeast needs fermentable sugar and vitamins, which spirulina doesn't need. Let's just focus on growing brewers yeast and forget wild yeasts like Candida albicans. After sugar and water, the biggest thing yeast needs is a nitrogen source, for which brewers often use diammonium phosphate (DAP), which can be made by reacting ammonia and phosphoric acid, and I've also seen ammonium sulfate is in laboratory work. You could also use hydrolyzed protein from spirulina or another easier to grow microorganism as a nitrogen source. Yeast also needs some other chemical elements, particularly phosphorous, sulfur, and zinc. Probably smaller amounts of potassium, calcium, iron, and manganese too. Lots and lots of growth medium nutrient mixes for yeast (sold as yeast booster for brewers) include a mix of B vitamins, but I haven't seen any paper establishing which ones are vital to the yeast as they are vital to human metabolism. Vitamins B1 and B5 are always included, and often (B3, B7, B9, inositol). My guess is that B1, B5, B7, and inositol and essential to yeast, and B3 and B9 don't hurt, and some of the yeast's vitamins just aren't always included in the growth media because it's assumed that the brewer will be using a fermentable sugar source like grapes or wheat that already has most of what the yeast needs. How much of the vitamins and elements does yeast need for a given amount of sugar and water? I don't know, but you can look at the nutrients in, e.g. beer wort or wine must to get upper limits. Like, green grapes have a low amount of B3 compared to other grapes (~0.1 mg B3 / 100 g must), so that must be enough for yeast, if indeed they need any.
Except do they need any? There's a modern Finnish alcoholic spirit called kilju (Is that pronounced "kill you" or "killed you"?) which is made by fermenting plain refined white sugar and water, which I wouldn't think would have any nitrogen or vitamins left. This confuses me. It seems to say that nitrogen and vitamins aren't essential to yeast, which is nonsense, because yeast has to make the proteins in its cells out of something. So I think either (1) The dry yeast you add to the kilju syrup contains nitrogen and other chemical elements and vitamins, and the yeast population doesn't really exceed the initial numbers of dry yeast cells put in, because there isn't anything for new yeast to build their cells out of, or (2) people add some nutrients to the kilju syrup and it just doesn't get advertised all that much. Oh, hey, wait, NileRed on Youtube made alcohol out of toilet paper that one time. That's kilju. Did he add nutrients? I can't remember. Regardless, you need fermentable sugar to grow yeast, which already makes it slightly harder to grow than spirulina if you don't have plants for some reason, like being on a planet where plants are hard to grow. And if you want to use the yeast as a protein source, and not just for fermenting carbohydrates, then you'll need some diammonium phosphate and zinc and vitamins to build up a culture. That makes it a little less attractive as a protein source for a space diet, but the growing conditions aren't terribly harsh, and it's nice to have a protein source in this diet that isn't algae. And it's good to have a fungus for vitamin D production.
Oh hey, here's a paper on what vitamins are actually vital to yeast. That could be useful for optimizing its growth medium.
Quorn:
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After we've finished talking about single-cell proteins as space food, I'll move on to extracellular synthesis of food molecules by microorganisms, both natural and engineered, with special reference to edible sugars and polysaccharides, microbial oil, and the vitamin B12.
:: Microbial Carbohydrates
There are some simple carbohydrates made by microorganisms. Yeasts in the genus Saccharomyces famously make ethanol from sugar, and Acetobacter makes ethanol into acetic acid. Where do you get the sugar, though? Fear not! A bunch of biologists at Harvard engineered a rapidly-growing photosynthetic cyanobacterium, Synechococcus elongatus, so that it would produce and export glucose and fructose. Amazing. They put sugar on the microbial menu. Thanks so much. Sugar is not just a big part of normal human diets, it's also important as an important feedstock for other microbial food-producers. One more carbohydrate: a yeast called Candida glycerinogenes is used industrially to make glycerol.
I'd like to be able to make complex carbohydrates, like plant starch, but from microorganisms. Plant starch is cool both because you can make lots of traditional food dishes from it and because it's digested more slowly than plain sugars. It's made of two polysaccharides: amylose and amylopectin. Amylose is made of glucose subunits connected by alpha-1,4 linkages (the linkage-type specifies which of the six carbon atoms in the first sugar molecular binds to which carbon atom of a second sugar molecule, and the prefixed greek letters alpha or beta tells you about the 3D geometry of the chemical bond relative to the planes of the carbon rings in the molecules.). Amylose can have a few hundred to a few thousand glucose links in a line. It's digested slowly and is not very water-soluble. Amylopectin on the other hand has short (alpha-1,4 linked) chains of about 25 units, and they're all bound together by occasional branches of alpha-1,6 links. The chain length of amylopectin varies a little bit with the plant species. Amylopectin is digested more rapidly than amylose because of the shorter chain length. It's also more water-soluble. I can't find glycemic index numbers on the pure polysaccharides, but based on the G.I. numbers for starchy foods with different amounts of the two, I'd guess that amylose is around 35 and amylopectin is around 80. Boiling starch, as one does, also breaks down some of the linkages and increases its glycemic index. For comparison, molecules with short alpha-1,4 glucose chains (3 to 17 units) and no branches are called maltodextrins, and they're digested as fast as unlinked glucose (G.I of 100).
Can we make cool slowly digestible polysaccharides using microorganisms?
Maybe. Microorganisms are good at constructing large molecules outside of their cells. Most of these "extracellular polymeric substances" or EPSs are polysaccharides, but structural proteins, enzymes, nucleic acids, triglycerides, and a few other things are also included - even a class of biodegradable plastics, polyhydroxyalkanoates. It would be wonderful if we could get bacteria or yeast to export globular proteins like those found in egg whites, wouldn't it? A few minutes after I wrote that sentence, I found that Justin Atkin and his team at the Thought Emporium are trying to engineer yeast to make egg whites and deer milk. Deer milk? Apparently, so. This is relevant to my interests. But let's talk about carbs first. Xanthan gum is a famous EPS polysaccharide used as a food thickener, but the human body can't digest it. Technically, gut bacteria can partly digest most indigestible fibers, but the bulk of it still passes through you, and you can't live off of their scraps, so I'm not counting that. Alginate and welan are a little less famous, but also used as food additives. And they're also indigestible.
The biofilm that holds together grains of yeast and Lactobacillus bacteria when you make kefir from milk consists of an EPS polysaccharide called kefiran that's made of glucose and galactose. Some of the EPS polysaccharides are fructans (polymers of fructose) and the human body can't digest any of those. Some of the other ones are glucans (polymers of glucose), among which we can digest the ones with alpha linkages, but not the ones with beta linkages (like cellulose, curdlan, lichenin, and zymosan). Chitin is a polysaccharide in mushrooms and arthropod shells that's also a microbial EPS. It's basically a beta-glucan, except the glucose molecules all have a weird nitrogen group sticking off of them called acetamide. There is a polysaccharide in Spirulina called immulin and one in Chlorella pyrenoidosa called immurella. I don't think either one is digestible or made in significant quantities.
One alpha-glucan EPS that humans can digest is pullulan, made by the unicelular fungus Aureobasidium pullulans. It's a black yeast-like thing. You feed it glucose and it links up the molecules. The glucose subunits in pullulan are linked together in the same way as amylopectin, but with a shorter chain length (3 units). Pullulan is a component of those quickly dissolving thin-film breath strips (LISTERINE® POCKETPAKS®), and it's a coating on pills like Benadryl, and it has some other dietary applications. But it's hard to make in bulk, and with its short chain length, it's not like plant starch at all. You can't make pasta from it because it's too water-soluble, and the short chain-length means it's probably rapidly digested and has a high glycemic index.
Oh, wait, no. "Pullulan Is a Slowly Digested Carbohydrate in Humans" (Wolf et al, 2003). And that's a response to older papers calling pullulan indigestible. Weird. Maybe the starch granules are reall tighly packed and enzymes can't get at them? I'll let you know. I still don't think you can make pasta out of it, but maybe pullulan has some use as a complex carbohydrate in space diets.
There are at least two other alpha glucan polysaccharides made by microorganisms. First, dextran is a bacterial EPS. Second, Floridean starch is made by glaucophytes (a unicellular alga), but I think it's always built internally to glaucophyte cells, not as an EPS. They might work for space diets. I'll look those up. And some bacteria build glycogen internally. Glycogen is technically more than a carbohydrate: it's a giant mass of polysaccharides surrounding a big protein enzyme, but if we can make lots of it, it might be suitable as a carbohydrate. I'll look into that too.
Dextran has alpha-1,6 linked chains, and branches that are alpha-1,3 linkages. It's made by some lactic acid bacteria when given sucrose. Doctors put it into people's veins, where it does a few things. It reduces clotting, for one. It's also an osmotic agent, which, I think in the context of the bloodstream means it doesn't leave the blood through the kidneys, and because it sticks around, it displaces water in the blood (or increases the osmotic pressure), so that water from the bloodstream moves into surrounding tissues. Maybe. Or the water moves the other way. I don't know. The important thing for diets is, after administration, it can last in your blood for more than a week before being fully digested as glucose. To me, that sounds like very low but non-zero digestibility. It's used a little bit as a food additive, but like, as an emulsifier or a texturizer, not as a bulk calorific carbohydrate. I need to read more to find out what happens when you eat it in quantity.
Floridean starch:
Bacterial glycogen:
Ah! Maybe I shouldn't have been looking at extracellular products at all. Intracellular alpha-glucan storage-polysaccharides like Floridean Starch and glycogen are where it's at! See "Physicochemical Variation of Cyanobacterial Starch, the Insoluble α-Glucans in Cyanobacteria". That just leaves the challenge of getting it out the cells, maybe?
While investigating whether anyone has engineered a microorganism to produce amylose extracellularly, I found "Enzymatic transformation of nonfood biomass to starch", which uses a cell-free enzyme system to convert cellulose into amylose. Getting close. Getting close.
Hm. Unrelated, but Glucerna products use sucromalt, a slowly-digested oligosaccharide made by lactic-acid bacteria. That sounds cool too.
Ah, "Synthesis of novel α-glucans with potential health benefits through controlled glucose release in the human gastrointestinal tract" (Gangoiti et al., 2018). That looks good.
Actually forget that. I now see lots of papers about microbes that make amyose and I can't imagine what I was doing wrong with my searches in the past, but regardless, may I present for your consideration:
"Amylose-like polysaccharide accumulation and hyphal cell-surface structure in relation to citric acid production by Aspergillus niger in shake culture" (Kirimura et al., 1991), and also
"Characterization of a renewable extracellular polysaccharide from defatted microalgae Dunaliella tertiolecta" (Goo et al., 2013) (nominative determinism?), to say nothing of
"Crystalline amylose from cultures of a pathogenic yeast (torula histolytica)" (Hehre et al., 1948), or even
"Biochemical Investigation on the Capsule-Amylose Relationship in Cryptococcus Laurentii" (Foda et al., 1972), and apparently even Chlorella makes amylose starch, and you can read all about it in
"Reserve, structural and extracellular polysaccharides of Chlorella vulgaris: A holistic approach" (Ferreira et al. 2020).
So maybe microbial starch is easy and we can make that as a significant source of calories for a space diet. Sounds better than Imhausen fatty acids and glycerol.
:: Microbial Oil
In addition to single-cell proteins, there are single-cell oils.
Arachidonic acid (AA) is a conditionally essential fatty acid for adults, and just plain essential for infants. It isn't made by any higher plants. Animals can make some AA from other fatty acids, and some bacteria and fungi can make it too. Unicellular fungi in the genus Mortierella are especially good at making it, and several companies around the world use Mortierella alpina as a cheap source of arachidonic acid for infant formula. It's cheaper than using egg yolks for example. Mortierella alpina likes to eat sugar, but it will also produce when fed glycerol.
Docosahexaenoic acid (one of many biological compounds called DHA) is also essential for infants. And like AA, DHA is made by animals but not by any plants, so far as I can tell. There are a few single-celled organisms that make it though. Some infant formula manufacturers get their DHA from Crypthecodinium cohnii, a non-photosynthetic dinoflagellate. Dinoflagellates are too weird classify except genetically. They are eukaryotes, having organelles. They are motile and most are photosynthetic. We used to put them in the junk drawer of eukaryotes that aren't plants, animals or fungi, namely the protists. Historically, within the protists, botanists have called them protophyta (plant-like things, including red algae) and zoologists have called them protozoa (animal-like things, including amoebae). Genetically, dinoflagellates are now called alveolate myzozoa. DHA is also made industrially by two more protists, Schizochytrium and Ulkenia.
Gamma-linolenic acid can be made by Cunninghamella echinulata, a pin mold fungus, and by the fungus Mortierella isabellina.
I haven't written about chlorella as a protein yet, but if you don't give it enough nitrogen, it starts producing lots of edible oil for some reason. I don't know much about the oil or its fatty acid content, but it would be great if chlorella could be used for protein and fat and vitamin B12.
There are tons of oil-producing microbes, "oleaginous" ones. Lots for me to research. Like, I don't yet know which if any are good sources of the essential fatty acids LA and ALA.
:: Microbial Vitamins
:: Merits and Difficulties Of Microbial Manufacture
: Nutrients, Pathogens, Bioreator Designs
: Spirulina, Urine, and You
:: Microbial recycling
We've already talked about physiochemical methods for recycling biological waste into food, water, and gaseous oxygen. On earth, sewage is largely recycled by microbial methods. Wastewater treatment facilities are secretly bug farms, using anaerobic bacteria and aerobic bacteria in stages. Fungi also play a big role, and some of them are unicellular. I will talk about those bugs a bit. And a little bit about getting O2 from waste CO2.
MELiSSA is a microbial Waste Treatment Facility design created by the European Space Agency (for use in space, of course). The main difference from municipal Waste Treatment Facilities is that MELiSSA has a spirulina tank in one stage, capturing waste nitrogen in edible protein and also producing O2 from waste CO2. Genius. I love spirulina so much. Let's talk about every stage of MELiSSA.
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The BIOS closed ecosystem research facility in Russia found that you could convert CO2 to O2 for one person using a photobioreactor containing Chlorella vulgaris with about 20 kg of water and algae spread over 8 m^2 of exposed surface, photosynthesizing under artificial lights. Eight square meters of Chlorella per person. How deep? I don't know. If we assume that all the mass is water, and assume the 8 m^2 was a flat face of a prism or cylinder, then the remaining dimension of the tank would be just 2.5 mm. That seems a little too shallow. I think normal depths Chlorella are a few cm. But I don't know that the tanks were flat and shallow and opaque on the sides. Maybe they were clear tubes. That's not uncommon for photobioreactors. Anyway, shallow tanks are adequate. You can stack a few up in a room with lights in between, if horizontal space is limited.
Part III: Botanical manufacturing of space food
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