Subreddit: r/FoodScience
User: u/No_Tomorrow_7644
Link: https://www.reddit.com/r/foodscience/comments/1gltry1/how_to_liberate_galactose_from_gaur_gum/
Original Post:
How to liberate galactose from gaur gum?
I'm trying to free galactose from guar gum for use in fermentation. I found a slide deck (page 35) stating that with a .5M solution of sulfuric acid, good results can be achieved by boiling for three hours.
This is my current plan:
Use 37g citric acid powder, 13g sucrose, and 20g of guar gum per cup of water where 1 cup is 237 ml. The sucrose is there because I’d like to also liberate its glucose.
Use iodine to test the starch level in a sample of the solution.
Test pH and add more citric acid if necessary.
Boil this solution for a long time, maybe start with three hours. I’d like to use the instant pot so I can forget about it, but that’s maybe not a good idea for my first attempt.
Periodically test pH and starch level.
Stop after either I don’t feel like watching it anymore or the guar gum seems to have been sufficiently broken down via a visual assessment of the viscosity and/or the iodine test.
Use calcium carbonate to neutralize the solution, which should produce water, carbon dioxide, and calcium citrate.
My goal is to end up with sugar water that contains about the same amount of galactose (and also glucose) as milk would have. I expect to end up with some fructose and mannose, too, but that would be okay.
Any thoughts on methods? Suggestions for improvements? I know that citric acid can’t achieve the same pH as the sulfuric acid, so should I heat it for longer or maybe add more guar gum? Having leftover guar gum is not an issue. Also open to other ideas for getting galactose from a nondairy source.
I did see a previous post that suggested using beta mannanase for creating partially hydrolyzed guar gum, but that’s a little different from what I’m trying to do.
Edit: oops, I know it’s guar gum, not “gaur” gum. Embarrassing to have a typo in the title.
My First Response:
Why are you using citric acid when the protocol calls for sulfuric acid? A 0.5 M solution of sulfuric acid is nowhere near the pH of even the most concentrated citric acid solutions. This is apples vs oranges.
If you’re trying to avoid mineral acids, you can’t replace them with organic acids. They’re not strong enough to hydrolyze that galactomannan bond. I’d recommend you use a cocktail of enzymes to achieve this, starting with cellulase and endo-β-d-mannanase:
User's Response:
“Why are you using citric acid” because I’m doing this in my kitchen and don’t feel comfortable handling .5M sulfuric acid in my kitchen. I would also prefer to eat calcium citrate instead of calcium sulfate.
I know that citric acid is much weaker, and I mention this in my post. I was hoping that perhaps boiling it for longer would achieve some hydrolysis. But it seems like you don’t think any of the galactomannan bonds can be broken this way.
I appreciate the links to the papers! Another concern I have, though, is that it looks like cellulase can be bought as a supplement, but mannanase is a little trickier to source.
My Second Response:
Yeah, it's a thermodynamic issue, not a kinetic issue. Sulfuric acid will fully hydrolyzed to give you a complete solution of hydronium ions (pKa = -3), whereas increasing citric acid concentration will maintain a very tiny equilibrium of fully dissolved hydronium ions, considering the first pKa of citric acid is only 3.1.
I'm sure if you were to run that reaction for several months to several years, you might get some yield, but that's not practical and you're more likely to lose material through unwanted side reactions anyway. You either need more heat (temperatures > 100 C under pressure using a hydrothermal autoclave reactor) or stronger reagents.
I would just source food-grade or pharmaceutical-grade galactose and ask for a specification or technical sheet requesting for how the ingredient was manufactured. It's often used for diabetic purposes.
Guar gum hydrolysis is a very difficult process to achieve at home, coming from someone who does this type of stuff professionally in their own home.
But IF you were deciding to do this anyway, I highly suggest you use food-grade phosphoric acid. You're still going to see less efficiency than sulfuric acid or hydrochloric acid for hydrolysis (the first pKa of phosphoric acid is still only 2.15), so you'll need to keep this reaction going for several days, but at least it's food-grade and you can fully precipitate/neutralize the phosphates with a calcium solution.
I would actually neutralize first with a known concentration of a sodium carbonate solution, then precipitate the phosphates with calcium chloride; the problem is that both calcium carbonate and calcium phosphates are insoluble, so you'll run into an issue where a calcium phosphate thin-film forms at the surface of the calcium carbonate microparticles, slowing down neutralization significantly.
The neutralization reaction also slows down as the concentration of acid drops, so you'll have to contend with that as well; for these types of hydrolytic reactions with mineral acids, usually you'll want to hedge with an overage of your base over the molar ratio requirement to ensure complete neutralization, even if it mucks up the flavor. I say this for the sake of food safety; at least phosphoric acid is found in actual foods and has been known to be tolerable at low concentrations.
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