Chemical Forums
Specialty Chemistry Forums => Citizen Chemist => Topic started by: saquiwej on January 11, 2015, 09:42:16 PM
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Hello,
I am just a hobbyist, so I apologize if my question will be somewhat out of place in this forum of chemistry gurus.
I intend to do some biochemical experiments with fermentation where the temperature and pH value of the ferment should be kept as close as possible to certain optimum values at which the enzymes involved are at their peak performance. As to the temperature, it poses no problem, I am equipped with an adjustable heater. The pH value, however gives me some concern. It is supposed to be roughly 5. I experimented a bit with 5% vinegar and have found that to 1 liter of tap water I had to add between 4-8 grams of vinegar to be around 5 pH as shown by litmus paper. Given the subjectivity of measuring with litmus paper, I tried to find out the required concentration by calculation as well. To do this, without grappling with theory, I took the practical approach to recur to an online pH calculator (http://www.thermidaire.on.ca/pc.html). In fact I have double checked on two different sites with identical results, so that the possibility of an error is slight. What strikes me is the enormous difference amounting to several orders of magnitude between the theoretical values and those obtained relying on the litmus paper experiments. According to the calculators roughly 0.02 grams of vinegar would lower the pH-value of 1 liter of water to 5. It is 200-400 times less than what I got with the litmus paper. 0.02 grams is much less even than a drop, but the litmus paper does not react to a drop in a liter, the threshold being around 10 drops. I would say that the calculated value is the correct one, but then is litmus paper totally useless? Its possibility of error is ±2 pH.
Taking the 0.02 grams as correct, the practical problem is how to add such an infinitesimal quantity of vinegar to the ferment. Or should I simply leave it as it is?
Any suggestions are welcome.
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Theoretical calculations assume pure water. You don't deal with the pure water.
I assume by litmus paper you mean an universal indicator? Or a real litmus?
This is a rather lousy way of precisely controlling the pH. Either look for a specialized, narrow range pH test strips, or invest in pH meter.
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Yes, I used an indicator strip sold for the purpose. So, you think that tap water is a bit basic, because of the salts dissolved and to compensate this, more acid is required to achieve pH 5?
Do you think that a cheap electronic pH meter would register one single drop of vinegar in a liter of water?
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It is not just a problem with water being basic, more like it contains buffers which stabilize its pH.
Most pH meters are sensitive enough to detect pH changes below 0.1 range. Problems with the cheap ones is less likely to be related to their sensitivity, rather to accuracy.
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If you were to add a known amount of a base such as sodium hydroxide to a known amount of acetic acid, you would create a buffer whose pH could be approximately known prior to measurement.
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I have heard about buffers. But again, a buffer solution supposes pure (distilled) water as its medium. Mineral salts in tap water might influence the outcome.
Moreover, it will serve for the fermentation of foodstuffs, so I can’t put just anything into it. I don’t know anything about the toxicity of sodium hydroxide, but I wouldn’t eat it. Is there any 100% harmful alternative?
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I have heard about buffers. But again, a buffer solution supposes pure (distilled) water as its medium.
No, it doesn't require pure water. The beauty fop buffers is that if you add enough of them you will shift pH of the solution to the buffer pH.
Mineral salts in tap water might influence the outcome.
Depends on the concentration - in typical tap water they should not interfere too much.
Moreover, it will serve for the fermentation of foodstuffs, so I can’t put just anything into it. I don’t know anything about the toxicity of sodium hydroxide, but I wouldn’t eat it.
Sodium hydroxide is corrosive when concentrated, but once it is neutralized it doesn't matter. And it is commonly used in food industry (although you would definitely need to use food grade reagent, not any).
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Thank you for the exhaustive answer. I owe you some explanations, I think. In fact I am working on a method to ferment grains at home. A lot of research has been done in this field, but very few, if any, with the goal to provide housewives or anyone taking the trouble to prepare their meals themselves, with a simple method to properly ferment grains before cooking. Keeping in view that the general population is aimed at, the procedure has to be kept as simple as possible. There are many sorts of grains and seeds consumed worldwide. Virtually all of them would profit of some kind of fermentation prior to cooking, in the way of increased nutritive value. It is a serious problem particularly in poor countries, but developed nations are also affected.
Now, the reason why I am trying to find a DIY method to make a pH 5 solution or buffer is that most grains need a slightly acidic medium for the native (endogenous) enzymes that break down antinutrients to work at their peak performance.
I hesitate as to using Sodium hydroxide. The fact that it is widely used in the food industry, unfortunately, is no guaranty as to its harmlessness. On the other hand I am not sure it is available at the grocer’s next door. At least here in France it is not the case. Is there any other substance with similar chemical properties that could be used with vinegar for the acid part, to make a buffer? Could not simple table salt fill that role? I am aware that the pH of seawater is around 8, but I am not sure salts can be used in buffers. It is also important that the resulting buffer should be gastronomically acceptable, so that too much salt or vinegar wouldn’t do.
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I am surprised you mentioned Sodium hydroxide (lye) for food use.
Most times I here of Sodium bicarbonate (Baking soda) for food use.
By the way I am reading information in these links
http://www.chemguide.co.uk/physical/acidbaseeqia/buffers.html
http://www.chembuddy.com/?left=buffers&right=toc
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I'm not going to remark on the relative merits of fermented grains, or the existence or not of antinutrients. However, humans have been fermenting grains to make beer since prehistory. If you want the endogenous enzymes to work, you merely have to get them wet. The only hard part would be drying them again quickly before other fermentation happens, and they either spoil or become beer.
Anyway, if you're looking for a safe, easy to find buffer, you may try to look at fruit juices. They contain the buffers you need, you'll just have to look up the correct ones. And deal with any flavor incompatibilities.
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Thank you all for your answers. I agree with you that humans have been fermenting grains from prehistoric times. It is a fact, however, that humans did not profit from the introduction of grains into their diet as a staple. Archeological findings show a sharp decline in health simultaneous with the beginning of agricultural lifestyle (as much as it can be judged from bones). Unfortunately not all grains and seeds do contain sufficient quantities of enzymes to break down antinutrients effectively. It is time for me to be more specific: I have in view phytates when I refer to antinutrients. The enzyme needed for catalyzing its hydrolysis is called phytase. There are many different varieties of this enzyme with slightly different chemical properties. Some of them are most efficient at neutral pH, like for example bean phytases, but cereal phytases require a slightly acidic pH. At neutral pH their catalyzing potential is considerably reduced (3 to 10 times). So that the fermentation would greatly profit from an acid buffer. What they do in traditional bread making is to inoculate the dough with a bacterial culture (sourdough). The bacteria lower the pH of the dough to just the ideal pH for the phytase to work. That’s all fine and nice, the only drawback is that you have to have a bacterial culture always ready at hand whenever you want to prepare some grain meal. It keeps for a week or two in the fridge, but it is rather fragile and you often find it spoiled. I will ask for advice in a microbiological forum as well, as to methods to maintain a bacterial culture alive for longer periods of time. The big advantage of using a buffer solution would be that one wouldn’t depend on delicate bacterial cultures and could prepare a grain meal any time (after a fermentation of a couple of hours). Most of the experiments performed with the view to study the hydrolysis of phytates were done using buffers rather than bacteria, so that it works for sure. What worries me in fact is that the pH has to be kept between pH 5 and 6. If it reaches 4 because of too much acid, it kills the process, than it is better to keep the pH neutral. What you say about fruit juices is new to me. I have heard, for that matter, that some people use fruit juices for adjusting the pH, but I always though it a barbarism used only by dilettantes. But if I understand you right, some fruit juices have the properties of an acid buffer in that they stabilize the pH rather than lower it in an uncontrollable way. Would it practically mean that using a certain fruit juice one could approach a target pH without the danger of overshooting it? The explanation of this, I reckon, is that fruit juices contain some mineral salt as well, in addition to the acids.
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1. Sourdough can be kept alive - you mix a sample with a flour and keep it in a warm place, then it is ready to survive another week in the fridge.
2. AFAIK bacteria in the sourdough are not only there to keep the pH at a correct level. They are also responsible for part of the fermentation, so just replacing them with a buffer is not enough to replicate sourdough.
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2. AFAIK bacteria in the sourdough are not only there to keep the pH at a correct level. They are also responsible for part of the fermentation, so just replacing them with a buffer is not enough to replicate sourdough.
Yes, the reason it is "sour" is because of lactic acid produced during fermentation. If you don't have lactobacilli fermenting, it ain't sourdough. You can use chemical buffers and leaveners to make bread - e.g., soda bread - but this is a very different type of bread, and it tastes and feels very different from sourdough and other breads that are leavened with microorganisms. (Although, since must soda breads are made with buttermilk, which is fermented by lactobacillus, then I guess even soda bread is ultimately made by via microbiological fermentation. But the lactic acid from buttermilk is neutralized with the carbonate, this is why soda bread don't have sourdough's characteristic tang.)
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I agree with you both in what you say about sourdough. Though I referred to sourdough in my explanations, it is not sourdough in the first place what I have in mind when I am talking about fermentation. But it’s me who have chosen the incorrect term, for I am aware now that fermentation always assumes the involvement of some kind of microorganisms, or yeasts in the process. So, for more precision, I am going to call the process dephytinisation instead, which term is scientifically more correct. Dephytinisation means a process (chemical/or biological) by which phytates are broken down in a mixture. You are right in saying that in bread making bacteria and yeasts are playing an important role. It is a proven fact, however, that the breaking down of phytates in bread occurs almost entirely enzymatically. The role of microorganisms is to develop carbon dioxide and thus to make the dough swell, and to lower the pH to the optimum level. The characteristic taste is just a byproduct. I have never personally tried my hand at bread making; luckily, good quality sourdough breads are available at some organic groceries nearby. Traditional sourdough fermentation results in almost complete dephytinisation, so there is no room for much improvement there. What I have in mind is not breads, but: 1) porridges, 2) liquid mixtures used for pancakes and tortillas, 3) pastas 4) whole grains (like rice and beans). These products are not available in dephytinised form on the market. That is, the only type of dephytinisation actually practised is mechanical, when wheat and rice kernels are deprived of their outer layers which contain the phytates. Unfortunately vitamins and most of the minerals are also discarded this way.
In order to convince you that what I am driving at is no nonsense, please, consider the following, almost anecdotal fact: In animal husbandry, especially in pork raising, it is a well established experience that pigs grow much faster and are healthier if their cereal based feed is dephytinised. Phytates are powerful chelators, that is, they bind free minerals like calcium, magnesium, zinc, and iron, to mention only the most vital. It practically means that though someone might consume sufficient quantities of these minerals, if they are consumed together with foods containing large amounts of phytates, they never reach the small intestine, where they could be absorbed by the organism, but are evacuated as a waste. The direct consequences are osteoporosis, stunted growth, dental caries, indirectly a phytate-rich diet can be involved in the pathogenesis of any conditions where mineral deficiency plays a role. Pigs, as a race, are very similar to humans as to their metabolism. I mean that they are omnivorous and monogastric mammals just like us. So, it stands to reason to assume that the way in which they digest phytate-rich food, is very similar to our way of digesting it.
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This wall of text is hardly readable, but I did my best.
You are right in saying that in bread making bacteria and yeasts are playing an important role. It is a proven fact, however, that the breaking down of phytates in bread occurs almost entirely enzymatically. The role of microorganisms is to develop carbon dioxide and thus to make the dough swell, and to lower the pH to the optimum level.
So you are saying yeast and bacteria doesn't supply required enzymes at all?
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I am sorry that you find my post difficult to read. I am not sure, whether you are hinting at my English, or rather to the incorrect use of some technical terms. I tried to be as clear as possible. I have never been very good at punctuation, so, a comma might be missing here and there.
Bacteria produce some phytase, for sure, which contributes to dephytinisation, the same as the endogenous phytase. What I am saying is only that in case of enzyme-rich cereals, such as wheat and rye, which are principally used for bread-making, the role of bacterial phytase is minimal. The reason people are using sourdough, or bakers yeast, for that matter, is not to break down phytates present in the dough, but to make it swell and more palatable. The phytates would break down even if there were not a single microorganism in the dough.
My other point was that people make great efforts to dephytinise pig feed, but no one really cares what people eat. I am trying to work out a simple method to dephytinise grains at home. A fool-proof acid buffer (pH 5 - pH 6) would be a great asset to achieve this end.
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Wall of text - you are not splitting your text into paragraphs, which makes reading challenging. Other than that it is OK for me.
Safe (in terms of consumption/food stuff) pH 5-6 buffer would be one based on the citric acid and its sodium salts.
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Good idea about citrate. It will buffer well in a broad region of pH values.
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Thanks for the suggestions. I see now that I’ll have to do a bit of experimentation myself. It seems that there is no ready for use recipe for an acid buffer to be used with foods. For my experiments I will need a reliable pH meter with a precision of ±0.5 pH. Could anyone suggest a brand? I am thinking to pay up to 30€. Is it true that a pH meter needs to be calibrated before each measuring?
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Is it true that a pH meter needs to be calibrated before each measuring?
Perhaps not literally before "each", it should be enough to check the calibration once per each series of measurements, or once daily, but it definitely requires calibration if you want reliable results.