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Medical Forum / General / Nutrition / April 2008Why cannot we taste or smell the lipid peroxides in refined oils?
On the following Udo Erasmus site: http://www.udoerasmus.com/articles/udo/hbaco.htm he claims that refined oils contain 1% of damaged molecules to start with and are further oxidized when used in frying. I have also heard in other places that we cannot recognize how bad refined oils are using our senses, this works only for unprocessed fats like butter or virgin olive oil. But from the chemistry lessons I know that fatty acid aldehydes and peroxides have strong smell and taste of rancidity. How could this be that the industry manages to mask these properties? What are the additives which mask the smell? For instance 4-OHE (posted previously) has quite strong rancid smell in a pure form. But the cooking oils containing it are odorless. Also fried food doesn't have any rancid taste. Taka > On the following Udo Erasmus site: > [quoted text clipped - 11 lines] > pure form. But the cooking oils containing it are odorless. Also > fried food doesn't have any rancid taste. If anything is defective, I would say that it is your half-baked notion that all rancid or otherwise unhealthy oil must smell bad. I had a jar of coconut oil with just a little remaining. I forgot about it for over a year, then when I opened it, there was a distinct rancid smell. Also, I made a shortbread with a small amount of butter,then kept it in a sealed plastic bag in the refrigerator. After a couple of months, I opened the bag (after not eating any for a few weeks) and there was a strong rancidity smell. I've had olive oil that also had that strong smell to it, years ago, when I used small amounts of it (organic, first pressed, extra virgin). When relatives or friends eat fries or meat, I can detect what I think is a hint of rancidity, no matter how "fresh" the ingredients were before cooking. Another source claiming that we can smell the rancidity in unrefined oils but not in refined oils. This means that the processed oils can be odorless and tasteless and yet contain dangerous amounts of lipid peroxides: QUOTE: Rancid fats and oils taste very bad even in small amounts; people avoid eating them.[13] It is very difficult to measure or estimate the actual human consumption of these substances.[14] In addition, the majority of oils consumed in the United States are refined, bleached, deodorized and degummed by manufacturers. The resultant oils are colorless, odorless, tasteless and have a longer shelf life than their unrefined counterparts.[15] This extensive processing serves to make peroxidated, rancid oils much more elusive to detection via the various human senses than the unprocessed alternatives. UNQUOTE. SOURCE: http://en.wikipedia.org/wiki/Atherosclerosis > Another source claiming that we can smell the rancidity in unrefined > oils but not in refined oils. This means that the processed oils can [quoted text clipped - 13 lines] > > SOURCE: http://en.wikipedia.org/wiki/Atherosclerosis Wikipedia is not the primary source for that "information". Check the references. The source is Udo Erasmus, who is not a reliable source for information about fats and oils. His book cites many scientific articles in its bibliography, but they are not cited in the text. He says lots of true stuff as well as stuff that may or may not be true and stuff that is untrue, but he doesn't connect any of his statements to his sources, so you can't check them out for accuracy. He advocates many fringe theories, such as food combining (the theory that meat shouldn't be eaten together with starches [p. 32]) and homeopathy (the theory that extremely dilute solutions of toxic materials can have medicinal properties [p. 87]). Like all effective propaganda, his book is a mixture of fact and fiction, with no help to the reader in determining which is which. Don't be fooled by the thin veneer of science he wraps his theories in -- he's just trying to sell you his theories (and his line of Udo's Choice oils). And even common sense should tell you that the notion that refined oils are rich in oxidized oils is obviously bogus. If it were true that you can detect them at low concentration by smell only when the oil is in a raw, unprocessed state, then what you are smelling or tasting is not the oxidized oils -- it's whatever other stuff is present that's removed during refining. Hpwever, the fact is that you can detect these oxidized oils at low concentration. The notion that they are often present in refined oils is simply untrue. It's a myth made up by a charlatan who wants to be able to point at a perfectly wholesome product and convince you that there's something wrong with it, so that you'll be scared into buying his alternative oil. > However, the fact is that you can detect these oxidized > oils at low concentration. The notion that they > are often present in refined oils is simply untrue. I agree. The reason those oils are refined is to increase their shelf life, which means avoiding rancidity. On the other hand, refining also removes vitamin E, other vitamins and anti-oxidants, and minerals. So be careful with your oils. Don't buy the perishable ones in large bottles, and use the purified ones (like "pure olive oil," as opposed to virgin and extra-virgin), in moderation, and mainly for cooking, especially when you need a high smoke point. If you're concerned about the flavor, there are many natural oils with very subtle tastes. They're great for confections, gravies, sauces, puddings, and salads. Finally, remember that oils are rich in calories, so you need to get your essential fatty acids first. Fill up on fried chicken cooked in peanut oil, and you won't have room for that fancy salad with its delicious gourmet salad oil!  SignatureMarshall Price of Miami Known to Yahoo as d021317c Another source claiming that the cooking vegetable oils are generally safe and "EFAs" are not destroyed: http://www.essentialfats.com/fapfaq.pdf > with and are further oxidized when used in frying. I have also heard > in other places that we cannot recognize how bad refined oils are > using our senses, Humans survived the evolutionary process of killing off weaker species because of our superior brain. Our adoptive survival advantages do not come from our sense of smell, taste, or sight. Now, how about using your brain? >> with and are further oxidized when used in frying. I have also heard >> in other places that we cannot recognize how bad refined oils are >> using our senses, > > Humans survived the evolutionary process of killing off weaker species > because of our superior brain. ... We haven't survived that evolutionary process yet. We're fast approaching the point where destroying other species is going to have consequences far more wide-reaching and catastrophic than these all-too-human brains can possibly imagine. If we were really smart, we'd have figured out long ago how to control our cupidity, and we'd never have gotten into this mess. SignatureMarshall Price of Miami Known to Yahoo as d021317c > >> with and are further oxidized when used in frying. I have also heard > >> in other places that we cannot recognize how bad refined oils are [quoted text clipped - 11 lines] > If we were really smart, we'd have figured out long ago how to control > our cupidity, and we'd never have gotten into this mess. Perhaps, if you were to focus? My entire point was: Humans are not known for having an acute sense of taste. Our evolutionary strong point is a superior brain. But, obviously in your case you must have received a mutation that rent south in your brain-pan. :( Ha, .... Hah, Ha! Seems I have figured this out. It's not the lipid peroxides but trans- fatty acids what makes the refined(heat-treated) oils problematic. In another book I am reading now they state that the unsaturated fatty acids are known to flip their double-bond configuration at higher temperatures. Oxygen is not needed for this process. All refined oils are heat treated and also damaged this way when used for frying/ fritting. Also some highly unsaturated oils are known to be "molecularly distilled" at high temperatures. Trans fats are known to jam the lipid metabolism in mitochondria. Therefore I think that Peskin may be right afterall when talking about "adulterated" processed oils. Linoleic acid from cold-processed oils such as evening primose or in its natural context in plants may be in certain amounts healthy but the trans-linoleic acid present in heat-treated cooking oils such as corn or soybean is harmfull. Taka > Seems I have figured this out. It's not the lipid peroxides but trans- Ah, now you're changing your story. Your first story was not supportable, so now you move on to a new one. > fatty acids what makes the refined(heat-treated) oils problematic. In > another book I am reading now they state that the unsaturated fatty > acids are known to flip their double-bond configuration at higher > temperatures. Oxygen is not needed for this process. All refined > oils are heat treated and also damaged this way when used for frying/ And you know this how? Certainly, unsaturated fatty acids can flip if heated to a sufficiently high temperature in the presence of a suitable catalyst. But are refined vegetable oils heated to such a temperature? And in the presence of a catalyst? You don't say "I think it's possible that . . ." or "Maybe it could be . . .". You assert as a statement of fact that these refined vegetable oils have a significant amount of trans-fats as a result of being heat-damaged during refining. Do you make this assertion based on any data, or is it like your previous assertions -- nothing but blowing smoke? Where is the actual data showing these significant levels of trans-fats in refined vegetable oils? > fritting. Also some highly unsaturated oils are known to be > "molecularly distilled" at high temperatures. Trans fats are known to [quoted text clipped - 4 lines] > amounts healthy but the trans-linoleic acid present in heat-treated > cooking oils such as corn or soybean is harmfull. In God we trust. Everybody else bring data. > > Seems I have figured this out. It's not the lipid peroxides but trans- > > Ah, now you're changing your story. Your first story was not > supportable, so now you move on to a new one. It is supportable, there are mutagenic lipid peroxides in cooking oils such as commercial perilla oil even if they don't smell bad/rancid: Mutat Res. 2006 Feb 28;603(2):186-92. Epub 2006 Jan 19. Detection of 4-oxo-2-hexenal, a novel mutagenic product of lipid peroxidation, in human diet and cooking vapor. Kawai K, Matsuno K, Kasai H. Department of Environmental Oncology, Institute of Industrial Ecological Sciences, University of Occupational and Environmental Health, 1-1 Iseigaoka, Yahatanishi-ku, Kitakyushu 807-8555, Japan. Since the diet plays an important role in the development of human cancer, it is important to identify mutagens in foods. We have detected a novel mutagenic product, 4-oxo-2-hexenal (4-OHE), in a model lipid peroxidation reaction mixture [H. Kasai, M. Maekawa, K. Kawai, K. Hachisuka, Y. Takahashi, H. Nakamura, R. Sawa, S. Matsui, T. Matsuda, 4-Oxo-2-hexenal, a mutagen formed by omega-3 fat peroxidation, causes DNA adduct formation in mouse organs, Ind. Health 43 (2005) 699-701]. In the present study, the contents of 4-OHE in various food samples were determined by a GC/MS method. Commercial perilla oil (derived from the seed of Perilla frutescens var. frutescens), which is rich in linolenic acid triglyceride (TG), the edible part of broiled fish, and various fried foods contained 4-OHE in the range of 1-70 microg/g. Furthermore, from the ethyl acetate trap (extracts) of the smoke released during the broiling of fish, 4- OHE was also detected by GC/MS. These results provide a warning to humans, who may be exposed to this mutagen. The 4-OHE may be produced from omega-3 polyunsaturated fats, such as alpha-linolenic acid-, docosahexaenoic acid (DHA)- and eicosapentaenoic acid (EPA)-TG, which are more easily oxidized than omega-6 fats, such as linoleic acid-TG. PMID: 16423557 > > fatty acids what makes the refined(heat-treated) oils problematic. In > > another book I am reading now they state that the unsaturated fatty [quoted text clipped - 13 lines] > significant amount of trans-fats as a result of being > heat-damaged during refining. There are trans-fats in common cooking oils even in the liquid ones, e.g.: Am J Clin Nutr. 1978 Jun;31(6):1041-9. Links Trans-isomeric fatty acids present in West German margarines, shortenings, frying and cooking fats. Heckers H, Melcher FW. Fatty acid patterns were determined in 83 brands of margarine, 9 brands of low-calorie margarine and 18 brands of shortening, frying and cooking fat purchased at random from the retail marker in the Federal Republic of Germany in 1973/1974, and a second time in 1976. As a result of gas-liquid chromatographic analyses on a Silar 10 C coated packed column, complemented in some cases by the values recorded on a highly selective SP 2340 capillary column, trans- octadecenoic acids ranging from 53.2 to 0.1% were measured. None of the products examined was completely free of trans-fatty acids. High values of trans-octadecenoate were always accompanied by positional isomers of cis-octadecenoate, by 9trans,12trans-octadecadienoate and by 9cis,12trans-octadecadienoate and 9trans,12cis-octadecadienoate. Furthermore, two mixed geometric isomers derived from linolenic acid (probably 9cis,12cis,15trans-octadecatrienoate and 9trans,12cis,15cis- octadecatrienoate) could be identified, provided that the individual brand contained sufficient linolenic acid. Following partial hydrogenation, transhexadecenoate, 0.1 to 0.2%, was detected in some of the edible fats. PMID: 665548 > Do you make this assertion based on any data, or is it > like your previous assertions -- nothing but blowing [quoted text clipped - 11 lines] > > In God we trust. Everybody else bring data. But PUFAs generally can do more harm than trans-fats. Hum Nutr Clin Nutr. 1984 May;38(3):223-30. Trans-unsaturated fatty acids in margarines and human subcutaneous fat in Israel. Enig MG, Budowski P, Blondheim SH. Representative Israeli dietary fats were analysed by capillary gas chromatography, with emphasis on the trans-fatty acid (FA) content. The percentages of trans-monoenes were relatively high: 28.5-30.4 in three hard margarines, 13.4 in both of two soft margarines, but 0 in both of two cooking oils and 27.6 for a sample of commercial cookies. The corresponding percentages of trans-dienes were 0.4-0.5, trace-0.9, 0-0.1 and 0 (one oil sample had 0.6 had 0.6 per cent trans-triene). For cis-polyunsaturated FA the percentages were 26.4-28.7, 39.7-41.6, 60.6 and 18.2 respectively. P/S ratios for the hard margarines were 1.69-2.01, higher than those of American margarines, which are about 1.40. When trans-FA were included with the saturated FA, the ratios were almost equal, 0.52-0.60 versus 0.53, respectively. In the subcutaneous fat of 8 Israelis of various ethnic origins and dietary habits, total trans-FA averaged 4.5 per cent (range 1.9-6.6), similar to that in the US and UK. However, the percentages of polyunsaturated FA in the Israelis were very high, 27.2 (20.3-32.3) for linoleic acid and 1.5 (1.0-1.8) for linolenic acid. The average P/S ratio was also very high, 1.19 (0.80-1.60) and P/(S+trans) was 0.98 (0.67-1.37). PMID: 608655 > > > Seems I have figured this out. It's not the lipid peroxides but trans- > > [quoted text clipped - 3 lines] > It is supportable, there are mutagenic lipid peroxides in cooking oils > such as commercial perilla oil even if they don't smell bad/rancid: Where in this citation does it say that the peroxides can't be smelled? That was the original, bogus assertion. Only 1 ppm of peroxides does not seem significant. The larger amounts in the smoke from burned oils could be significant, but all bets are off once you start burning any oil. > Mutat Res. 2006 Feb 28;603(2):186-92. Epub 2006 Jan 19. > [quoted text clipped - 47 lines] > There are trans-fats in common cooking oils even in the liquid ones, > e.g.: This study is about margarine and shortening, not liquid vegetable oils. Margarine and shortening (which are solid fats, like Crisco) are produced by exposing liquid vegetable oils to high temperature in the presence of a catalyst. This is called "partial hydrogenation", and it is used to convert liquid vegetable oils into semi-solid form by making it more saturated. In this process, trans-fats are also formed. This study is irrelevant to the question of whether significant quantities of lipid peroxides are present in non-hydrogenated liquid vegetable oils. The fact that you do not understand this difference indicates that your knowledge about vegetable oils is very incomplete. > Am J Clin Nutr. 1978 Jun;31(6):1041-9. Links > [quoted text clipped - 40 lines] > > But PUFAs generally can do more harm than trans-fats. Sorry, you again flunk the course. This is another study about margarine, which is partially hydrogenated. This is not relevant to liquid non-hydrogenated vegetable oils. > Hum Nutr Clin Nutr. 1984 May;38(3):223-30. > [quoted text clipped - 22 lines] > very high, 1.19 (0.80-1.60) and P/(S+trans) was 0.98 (0.67-1.37). > PMID: 608655 > This study is about margarine and shortening, not > liquid vegetable oils. Margarine and shortening [quoted text clipped - 6 lines] > semi-solid form by making it more saturated. > In this process, trans-fats are also formed. I have seen many vegetable LIQUID oils which have written on the label "modified for use at high temperatures/frying" or similar what can mean only that they are partially hydrogenated. How would you otherwise modify a PUFA rich oil to be suitable for cooking at high temperatures? Of course there are also the new genetically bred variants of safflower rich in oleic acid which is a MUFA and therefore more suitable for use at high temperatures but this is not what I have on my mind. The "olein rich" labels appeared only recently while the "modified for high temperature frying" have been around at least for 20 years ... Taka Wikipedia on cooking oils: http://en.wikipedia.org/wiki/Cooking_oil > > This study is about margarine and shortening, not > > liquid vegetable oils. Margarine and shortening [quoted text clipped - 10 lines] > "modified for use at high temperatures/frying" or similar what can > mean only that they are partially hydrogenated. How would you At least in the U.S., partially hydrogenated oils must be labelled as such. If the label doesn't say that the oil has been partially hydrogenated, then it has not. It's as simple as that. I've never seen a label description for a liquid vegetable oil that mentioned partial hydrogenation. I've only seen that on margarine and shortening. > otherwise modify a PUFA rich oil to be suitable for cooking at high > temperatures? Of course there are also the new genetically bred There's several ways you could modify a vegetable oil for high temperature work. One is to blend it with other oils that have good high-temperature characterisitics, such as coconut oil. Another is to add antioxidants to inhibit breakdown. Either of these would have to be indicated on the ingredients list. Another, but which would not need to be indicated, is to partially freeze the oil and separate out the fraction that freezes first. By doing this repeatedly, you can separate a liquid vegetable oil into its high-melting point and low-melting point fractions. The high-melting fraction will have better resistance to thermal breakdown, so it will be a more stable frying oil. The low-melting fraction is called "winterized" oil, because it will resist freezing at low temperature. > variants of safflower rich in oleic acid which is a MUFA and therefore > more suitable for use at high temperatures but this is not what I have [quoted text clipped - 5 lines] > > Wikipedia on cooking oils: http://en.wikipedia.org/wiki/Cooking_oil > Where in this citation does it say that theperoxides > can't be smelled? That was the original, bogus assertion. [quoted text clipped - 4 lines] > could be significant, but all bets are off once you > start burning any oil. So are you saying that the foods fried in the cooking vegetable oils are safe to consume and even beneficial sources of EFAs as long as they don't smell bad (given that you compensate for the n-6/n-3 ratio by eating some fatty fish)? Taka > > Where in this citation does it say that theperoxides > > can't be smelled? That was the original, bogus assertion. [quoted text clipped - 9 lines] > they don't smell bad (given that you compensate for the n-6/n-3 ratio > by eating some fatty fish)? They might be. I've always used fresh oil when frying, because I've noticed off-flavors indicative of breakdown when saving oil for a second batch. But deep-frying in general is not healthful because of the high fat content of the food. I haven't deep-fried anything in years. Commercial frying operations use highly saturated fats because of their longer lifetime in the fryer. Those are much more unhealthful, because of their role in producing cardiovascular disease. Animal fats, coconut oil, and partially hydrogenated oils are most commonly used for commercial frying. In the last 10 or 20 years, most brands of potato and corn chips have switched from partially hydrogenated oils to natural vegetable oils. I have no idea how they deal with the oxidation of the oils. They might be conducting frying operations under a nitrogen blanket, to prevent oxygen from reaching the oil. >>> Where in this citation does it say that theperoxides >>> can't be smelled? That was the original, bogus assertion. [quoted text clipped - 28 lines] > be conducting frying operations under a nitrogen > blanket, to prevent oxygen from reaching the oil. The best Japanese tempura restaurants use techniques that leave very little fat on the food. It never gets to penetrate the batter, much less the food inside. That's why it looks funny to us. Instead of a greasy, irregular surface, as you see on American fried chicken, the surface is smooth, dry, and pale, and the batter is soft and fluffy inside and crisp on the outside. I suspect the food is actually steam-cooked, by steam escaping from the batter. I don't know how they do it (the secrets are closely guarded), but these things must be important: the small size and weight of the fried pieces (to keep the oil immediately around them from cooling too much); the temperatures of the food and batter; the make-up of the batter (it contains eggs, I know, and it's rather watery); the preparation of the pieces (dry, uniform in size, and already warm); the type of oil used (peanut? lard?); keeping the pieces well separated during cooking; using brief cooking times; and how they get the oil off afterwards (first by placing them on a rack and turning them, then with paper towels). They never cook big pieces of chicken the way we do. They chop it into small pieces with a cleaver. On the other hand, they do leave bones in and skin on, which I don't like. The seafood and vegetables are much nicer. The only time I have deep-fried food is when I eat tempura at my favorite sushi restaurant -- which is averaging about once a year nowadays. They make tempura ice cream, too, but not for me! ;-) SignatureMarshall Price of Miami Known to Yahoo as d021317c > They never cook big pieces of chicken the way we do. They do make deep-fried battered pork cutlet in pieces as big or bigger than a whole chicken breast. It's called tonkatsu. > > They never cook big pieces of chicken the way we do. > > They do make deep-fried battered pork cutlet > in pieces as big or bigger than a whole chicken > breast. It's called tonkatsu. Yeah, if you think Japanese don't consume much fried foods you are mistaken. And they don't bother about the trans fats yet. Tempura is fried in highly unsaturated vegetable oil so it gets you later when it oxidizes inside the body. Many older Japanese are walking like Parkinsonian zombies, hard to say it is the PUFAs or the SOY ... Fish oil and antioxidants suppress inflammation and iron sequestering with green tea may suppress lipid peroxidation but it is not the best way to get along ... Taka |
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