I like to read about chemistry, but I haven't done much in practice, and I'd like to change that. One task I've set for myself is to extract pigments in a dry form from juice and do so in a way that's food safe. Juice is basically sugar water, so I'll want to have pigment without water or sugar to feel successful. Some ideas:
1) Evaporate the juice at room temperature (perhaps near a desiccant) or in a low oven/dehydrator. This won't remove sugar, but it's a start.
2) Ferment sugars to alcohol and then evaporate or dehydrate. I've heard you can get pouches of powdered wine in Europe and that they still have a significant alcohol content. Even with ethanol being more volatile than water, evaporation might not be enough to get pigments separated from sugar/ethanol/carbohydrates. Maybe rinsing the powdered wine with water and evaporating again would help? Sounds like a lot of work, but maybe.
3) Fractional freezing. If you freeze juice or wine solidly and then let it thaw partially, you get concentrated liquid dripping off a block of clear ice which thaws more slowly. I'm not sure what if anything stays in the ice besides water. I've heard that salt will be concentrated in the concentrate, and not stay in the ice, and that's pretty cool, because it's moderately hard to separate salt from water. Pretty sure that sugars and pigments also stay in the concentrate. So maybe it's just ice in the ice. I think this is a better way to remove water from a solution if you care about preserving organic compounds, but it's also more work. But it's also less prone to growing yeast and mold.
4) Inedible solvents: After evaporating juice to dryness, next dissolve the powder in a non-water solvent, preferably one that's fairly volatile. Hopefully something will be dissolved in the new solvent and other things will not be dissolved - the latter can be filtered through coffee filter paper perhaps, and then you can evaporate off the solvent maybe. I hear that sucrose has much lower solubility in pure ethanol than it does in water, for example, so that might be a way to separate pigments from sugar. Ethanol, isopropanol, and acetone are increasingly volatile solvents that you can easily get in bulk at local stores. Suppose we try acetone - which is poison, but honestly not way, way more poisonous than ethanol. I don't know the solubility of sugar or plant pigments in acetone, but let's think about acetone for a moment anyway for illustration. If acetone is more volatile than ethanol, you might suspect that acetone would evaporate off better than ethanol - but if it's poison, then you'll also want pretty strong guarantees about evaporation before using the extracted pigments in food, so "evaporates more" might not be enough. Though I suppose you could wash with water and evaporate multiple times. How else might we remove acetone from an acetone + pigment solution? I hear acetone freezes way way down at -93 C. So if you can cool a solution of acetone + pigment + a little bit of water down to normal freezer temperature, maybe we can assume that any solids which form will be mostly non-acetone, since acetone doesn't freeze at such warm temps. This is just fractional freezing again, but now we're taking the solid portion instead of the liquid. I'm not super trustful of this: the same reasoning would lead you to think that you could separate methanol from ethanol by distillation, when in fact the mixture behaves differently from the the components and you just can't separate them with any degree of caution, slow temperature transition, or height of reflux. So maybe you also can't separate acetone + water mixtures by freezing. I don't know. Apparently DCM, dichloromthane, is volatile enough that you can use it to extract things-soluble-in-DCM and then evaporate the DCM off under a vacuum pump - where by "can" I mean NileRed did it and was willing to drink the result. DCM didn't separate sugars from pigments, but it's evidence that toxic volatile solvents might be useful even for food-grade chemistry.
5) Freeze dryers and rotovaps. Freeze dryers are a few thousand dollars. Rotary evaporates are only one thousand dollars. These aren't real options for me, but in principle, vacuums can help remove solvents from solutions.
6) Life Straws. You can filter soda through a Life Straw to get clear soda. Lots of people do it on youtube. I'm not sure where the filtered part goes when you use a life straw. Does it clog up along the full length of the straw? Sounds awful. Is it easy to get the clogs out by running water in the other direction or blowing? I hear backflow is part of regular maintenance for a life straw. Maybe you can filter juice of it's pigment with a life straw and then use backflow to isolate the pigment clogs. That would be cool. I've got a life straw, but I haven't used it. I'll probably try some other things on this list first - but it's an option for the future.
7) Centrifugation. Centrifuges can help clarify pulpy juice like orange and tomato - clarify as in remove suspended pulp, not remove pigment or sugar. I don't think they're going to do anything for the beet juice that I'm starting with. Moving on.
8) Crystallization. To crystallize things from solution, in principle, you reduce the solvent volume and/or reduce the temperature. Adding seed crystals can also help. But I've made concentrated sugar water solutions (simple syrups) and stored them under refrigeration and not gotten any crystals. So something is missing... oh! Rock candy. I have gotten sugar crystals from a solution. Haven't done it since I was a kid. Something to review. Although the crystals take on pigment/food dye of the solution, so maybe this isn't the right route for separating sugar from pigment. ....
9) Flocculation and precipitation. ...
9) Acid-Base Extraction. ...
No comments:
Post a Comment