Guest guest Posted October 16, 2004 Report Share Posted October 16, 2004 >~~~~> Who came up with the oxalate explanation for the drying? The Andeans? >Did anyone study the oxalate content? I'll try to look for the post in the >pile of unread email lying in my box. It occurs to me that if you leave potatoes out in the sun, there is likely to be some bacterial action there? The Romans put fish guts in a jar, out in the sun, to ferment them. There seem to be bacteria that eat oxalates (producing C02, I'd guess?). Also if they dried them on the dirt, maybe the oxalic acid binds to minerals in the dirt. Heidi Jean Quote Link to comment Share on other sites More sharing options...
Guest guest Posted October 16, 2004 Report Share Posted October 16, 2004 @@@ Suze: Basing conclusions > on just a few data points is not very useful. @@@ It's better than zero data points... :-) @@@ Suze: How do you suppose *baking* > a sweet potato could increase the vitamin C content 8 TIMES?? I have two > guesses. @@@ Suze, that's just water loss from cooking. The only meaningful way to compare nutrient content is by calories, not grams. Mike SE Pennsylvania The best way to predict the future is to invent it. --Alan Kay Quote Link to comment Share on other sites More sharing options...
Guest guest Posted October 16, 2004 Report Share Posted October 16, 2004 This excerpt is from LOST CROPS OF THE INCAS. [in addition to possessing ingenious farming systems and outstanding public works, the Incas and their forebears had remarkable ways to preserve food. One technique was to freeze-dry root crops. In the Andean uplands, the nights are so cold and the days are so dry that tubers left out in the open for a few nights and days become freeze-dried. Usually, the people help the process along by covering the tubers at night to keep off dew and by trampling on the tubers during the day to squeeze out the water released by the previous night's freezing.] I have no idea if that is related to the oxalates. Darrell http://books.nap.edu/books/030904264X/html/ Quote Link to comment Share on other sites More sharing options...
Guest guest Posted October 18, 2004 Report Share Posted October 18, 2004 > Re: OXALATES > > > >In a message dated 10/13/04 9:44:09 AM Eastern Daylight Time, >s.fisher22@... writes: >Ah yes, you are right. I meant that it dissipates... disappears. I don't >know where to. It's been a long time since I saw an autoclave in action. >_____ > >~~~~~> Well, it can't disappear. Either it gets recycled and reenters w >hatever is holding the source water, it condenses on the walls of >the autoclave, or >it exits the autoclave and enters the air surrounding the >autoclave. But it >can't " disappear. " If the oxalates can travel in the steam to >come out of the >vegetables, I wouldn't necessarily *assume* that they couldn't >travel further >in the steam. And if not, then presumably they'd be accumulating in the >autoclave... in any case, when vegetables are steamed and boiled, >the oxalates end >up in the source water, having travelled there with the steam. >_____ I understand. I just wonder where it dissipates *to*...I just don't remember having to empty out a tray our anything with our autoclave. But again, that was a long time ago and I might just not be remembering correctly. ____ >You may be right, although I'm still curious about the Andean Indians >reducing oxalates simply by drying yams in the *sun*. So far, most >or all of >the pubmed abstracts I've looked at discuss it being leached out into water >(except the one mentioned above, in which the oxalates DID leach into the >water, but it was attributed to the heat). Of course they're not interested >in ancient or traditional food preparation, so it's not likely they'd be >testing oxalate content after sun drying. LOL >____ > >~~~~> I'm not sure what research you're talking about that found >that Andeans >reduced oxalates by drying. In any case, sun-drying doesn't create a very >large amount of heat... > Depends on where you are, I'd imagine. But it certainly doesn't entail any leaching into water or steam. > >Possibly. But this brings up an interesting point. Remember that the USDA >data is VERY unreliable when it comes to determining nutrient values in >foods for several reasons. Chief among them is that the nutrient content of >a crop grown in one field as opposed to another can vary as high as several >hundred percent! Even those grown across the street from each >other can vary >significantly in their nutrient content. So unless they were testing a >boiled and baked potato grown very close together in the same field, the >numbers should be taken with a grain of salt when compared to one another. >Secondly, and my first point makes this moot for the most part, what was >their sample size? Sometimes, it's just a few specimens. Basing conclusions >on just a few data points is not very useful. >_____ > >~~~~~>Ok, I agree their data might be unreliable, but in the >absence of more >reliable data, I don't see what else to use. Moreover, since it >doesn't make >much sense to me that ascorbic acid would be very heat-labile, I >would assume >it isn't until I see evidence of dry heat causing significant >ascorbic acid >loss. I'm not saying there isn't any... but I haven't seen it; do >you have any >on hand? Have you seen any? Not that I recall, but I haven't ever thought of it till you brought it up. As for the USDA data, I'm not convinced that it's good to use AT ALL for most things. Certainly not to compare or to gauge the nutrient value of produce. >_____ > >Regarding comparing the vit C content of vegetables - here is something >interesting. I just compared the vit. C content of RAW sweet potato and >baked sweet potato (skin on). Both used only 4 test samples. The raw sweet >potato had 2.4 mgs vitamin C per 100 grams edible portion and the baked >sweet potato had 19.6 mgs per the same portion! How do you suppose *baking* >a sweet potato could increase the vitamin C content 8 TIMES?? > >____ > >~~~~> Quite simply: the moisture loss in baking concentrates the sweet >potato, so that water is not occupying mass, and all components of >the vegetable >increase in concentration when measured as a ratio of amount to >mass of the total >vegetable. >_____ Oh darn! The most obvious answer gets in the way of my brilliant theories! ;-) > > I have two >guesses. One - these sweet potatoes were grown in different soils and their >nutrient content reflects that. Two, the ascorbic acid in the *raw* sweet >potato is bound to something...maybe calcium? And the heat (dry >heat in this >case) unbinds them, thus increasing the ascorbic acid content (although it >could possibly be simultaneously destroying *some* of the ascorbic acid >content, as well). >_____ > >~~~~~~> Those are " valiant explanations " as my chemistry professor once >credited me for when I did a lot of thinking to come up with >clever explanations >rather than simple and more obvious explanations, but it is much >more simple to >assume that cooking is reducing the moisture content, since the vitamins >between raw and cooked are consistently higher in cooked, for that >reason. Good >thoughts, but probably not necessary. > >____ > Well, what's interesting is that the vitamin C content in regular potatoes *decreases* with baking, which contradicts what happens with the *sweet* potato. At first I hadn't seen regular raw potatoes listed, but just found it now. It has 11.4 mgs/100 grams raw, and 13.5 mgs/100 grams baked. You see why I think the USDA database is fairly useless? The regular potato data contradicts your explanation, which I agree is the most obvious one. But it's only based on 3(!) DATA POINTS. Any 3 potatoes in the United States can't possibly represent the nutrient profile of the millions of potatoes grown in this country. This is why I think it may be even MORE confusing to use USDA nutrient data to try to learn anything meaningful about nutrient content of produce. A possible exception might be the drastic decline in nutrients over several decades. >No, *Deb* posted about it. She said that when she was researching yams, >she'd read that the Andean Indians' traditional method of reducing oxalate >content in their " oca " (yams) was to leave them out in the sun for several >days before eating them either raw or cooked. That's actually the >first time >I've heard of potatoes eaten *raw* by an ancient culture. Perhaps she has a >URL or source where we can look into that interesting tidbit further... >_____ > >~~~~> Who came up with the oxalate explanation for the drying? >The Andeans? >Did anyone study the oxalate content? I'll try to look for the >post in the >pile of unread email lying in my box. The article she posted didn't say. I think it did say though that these potatoes only contained *soluble* oxalates. Perhaps they are more prone to destruction by heat or drying or fermentation, as someone else mentioned? > >____ > >Also, in your response you didn't address my comments below. Do >you have any >comment? > >>I don't think we can conclude based on that *one* study on one particular >>food item (or was it multiple varieties of foods?) that ALL insoluble >>oxalates remain intact in all foods regardless of soaking and >regardless of >>time and temp cooked. >____ > >~~~~> I don't think the number of studies matters except in that >replications >with comparable methods yielding different results would cast doubt on the >competency or honesty of the researchers, and, conversely, >agreeable studies >would further our confidence in the honesty and competency of the >researchers. >But since the study I mentioned (which did use a variety of foods, >but I don't >remember which ones or how many) showed in several different ways that the >oxalate loss is due to leaching into water, simple logic would >dictate that only >soluble oxalates would be lost. Since this simple matter of logic >agrees with >their results, there is, as yet, no reason to doubt that. > >Chris > OK. Although I would counter that the number of studies *does* matter, in general, due to the shear number of studies whose conclusions are wrong, fixed or skewed due to financial influences or sloppy work, which a large percent seem to fit under. However, the study you posted *seems* to be OK in terms of quality based on what you said, so perhaps it's reasonable to take it FWIW. Suze Fisher Lapdog Design, Inc. Web Design & Development http://members.bellatlantic.net/~vze3shjg Weston A. Price Foundation Chapter Leader, Mid Coast Maine http://www.westonaprice.org ---------------------------- " The diet-heart idea (the idea that saturated fats and cholesterol cause heart disease) is the greatest scientific deception of our times. " -- Mann, MD, former Professor of Medicine and Biochemistry at Vanderbilt University, Tennessee; heart disease researcher. The International Network of Cholesterol Skeptics <http://www.thincs.org> ---------------------------- Quote Link to comment Share on other sites More sharing options...
Guest guest Posted October 18, 2004 Report Share Posted October 18, 2004 In a message dated 10/18/04 9:45:20 AM Eastern Daylight Time, s.fisher22@... writes: Well, what's interesting is that the vitamin C content in regular potatoes *decreases* with baking, which contradicts what happens with the *sweet* potato. At first I hadn't seen regular raw potatoes listed, but just found it now. It has 11.4 mgs/100 grams raw, and 13.5 mgs/100 grams baked. You see why I think the USDA database is fairly useless? _____ ~~~~> No, you've confused me. Did you type that sentence wrong? You're showing the vitamin C increasing with baking as in the other example, not decreasing, which fits the explanation offered by me and Mike. (although if it didn't, it wouldn't mean the data were useless, it would seem to suggest that there is a large heat-induced loss of vitamin C). ________ The regular potato data contradicts your explanation, which I agree is the most obvious one. But it's only based on 3(!) DATA POINTS. Any 3 potatoes in the United States can't possibly represent the nutrient profile of the millions of potatoes grown in this country. _______ ~~~~~> Why do they even bother using three? It's my understanding that the USDA's positions is that nutrient composition is dependent on species and breed, and not affected by soil. So shouldn't *one* sample be sufficient? If they implicitly admit the need for a variety of samples, you'd think they'd use a lot more than three. _______ This is why I think it may be even MORE confusing to use USDA nutrient data to try to learn anything meaningful about nutrient content of produce. A possible exception might be the drastic decline in nutrients over several decades. ______ ~~~~~> I think that would be useless as well, because there are unresolved possible alternative explanations for the decline in nutrient value that is shown in successive USDA figures, mentioned in an article you posted a couple months ago, such as changes in the definition of " edible portion " over time. I was disappointed that that article ignored the criticisms it mentioned rather than attempting to refute them. ______ The article she posted didn't say. I think it did say though that these potatoes only contained *soluble* oxalates. Perhaps they are more prone to destruction by heat or drying or fermentation, as someone else mentioned? _____ ~~~~~> If they are heat-labile, then being in wet heat would probably have a greater rate of destruction than dry heat. But since I still haven't seen any evidence that oxalates are destroyed by heat, and since I really don't think sun-drying would generate all that much heat anyway, then I prefer to avoid that route of speculation. Heidi's thought about fermentation seems to be one of the best thoughts-- though it's also worth noting that if the oxalates are soluble, then it may be that as the water leaves the vegetable somehow the oxalates are drawn out with it. (?) _____ OK. Although I would counter that the number of studies *does* matter, in general, due to the shear number of studies whose conclusions are wrong, fixed or skewed due to financial influences or sloppy work, which a large percent seem to fit under. However, the study you posted *seems* to be OK in terms of quality based on what you said, so perhaps it's reasonable to take it FWIW. _____ ~~~~~> That a conclusion is unjustified can always be seen by reading the study and using one's head, and there could be 1000 studies with bad conclusions and one study with good conclusions, so the value of having 1001 studies over one study is negligible in that respect. Whether the work is sloppy can generally be found by reading the methodology (though human error could affect the measurements), and in the absence of any conceivable financial stakes of whether cooked vegetables' oxalates are destroyed by heat or leached into water, I'd think the question moot. Nevertheless, I did say that replication is important as an indicator of competency and honesty, which seems to be no different than what you're saying here, with regard to sloppy work and financial interests. (Although, again, I can't conceive of how a financial interest could have a stake in this question-- perhaps someone advocating an " oxalate destroyer " that used only dry heat? A competitor's " super-oxalate destroyer " uses wet heat? [hehe]) Chris Quote Link to comment Share on other sites More sharing options...
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