Posted by Larry Hoover on February 14, 2005, at 12:45:53
In reply to Fish oil: how fishy is too fishy?, posted by lars1 on February 4, 2005, at 10:17:02
> I've recently started taking concentrated fish oil and have purchased several brands to try to find one that's fresh and reasonably priced. From past postings on this board, it seems that fishy taste is a sign of rancidity, and rancid oil is not healthful to eat. However, I am wondering, how fishy is too fishy? With all of the brands that I bought, if I bite the capsule, I get a fishy taste that is definitely noticeable, but not overpowering. It's about the same as eating actual fish, like if I bought some salmon at the supermarket and baked it. I would think that since fish itself is healthy to eat, similarly-fishy fish oil should also be OK. How fishy are the best available brands?
>
> LarsI'll try and address the various components of this thread in one post....
As Chris said, it was a good question.
As has been pointed out, rancidity and fishy are too distinct smells. So, I figured I'd best take a look at the chemistry involved. Turns out "fishy" is primarily associated with two volatile molecules, dimethylamine and trimethylamine. Now, either one could arise from bacterial degradation of complex proteins, but that fishy odour is seldom associated with decaying meat, so I think it has to be something unique to fish. The likely source of dimethylamine would be DMAE(dimethylaminoethanol), which is abundant in fish, and a direct non-smelly precursor of trimethylamine called trimethylamine-N-oxide, abundant in cold-water fish (believed to depress their tissue freezing point, allowing them to survive in Arctic waters). It is also possible that either one could arise from oxidation of choline or inositol, which may be found in lipid-soluble phospholipids that may be coextracted with the fish's triglyderides (the actual fish oil).
Okay, so "fishy" may be an inevitable finding in fish oil, as DMAE is partly fat soluble. It's hard to know, but the most rigourous purification processes (those that eliminate the fat-soluble environmental pollutants) would also likely minimize fishiness. As lars said, anything that is fishy on the order of that seen in cooked fresh fish would be an acceptable amount of fishiness in a fish oil supplement, in my opinion. Probably hard to eliminate entirely, and as people don't tend to bite into those capsules anyway (capsules are meant to get things past the taste-buds without exposure), fishiness ought not to be a big issue.
Chris, I'm sorry that you have found e.g. Carlson's fish oil to be overpowering, but that may be due to mishandling by the store, or during shipment. Fish oil is perishable, no matter how well it is purified in the beginning. My experience with Carlson's is that it is about as non-fishy as I could imagine fish oil to ever be.
Okay, now about rancidity. Rancidity is the oxidative breakdown of unsaturated fats. Polyunsaturated fats are more susceptible to it because they have multiple reactive sites. Also, the products of those oxidative reactions are more likely to be volatile (and thus detectable by our rancidity detectors....errr..noses).
When molecular oxygen adds across a double bond in an unsaturated fatty acid (or two adjacent fatty acids simultaneously (or the same bond more than once)), the products can be alcohols, aldehydes, ketones, peroxides, or shorter chain fatty acids. Each and every one of these products is more volatile than is the parent long-chain polyunsaturated fatty acid. We have evolved rancidity detectors in the lining of our noses to warn us that a foodstuff might be stale and/or spoiled. These rancidity products are also bitter and/or sharp to the taste, if our noses don't seem to catch the drift. The message is, "seek fresher food".
If you've ever taken fish oil on an empty stomach, you'll know what "rancid fish burps" are all about. The oxidative breakdown of the fatty acids is catalyzed by stomach acid. What you don't want to do is to ingest fish oil that has already had a head start. So, buy it from a source with high turnover. Pay attention to expiry dates (that isn't always a good indicator; I just bought some fish oil on the net with many years yet on the expiry, but it is rancid). Mishandling can occur. One weekend spent in the hot sun on a truck used to transport the fish oil from the manufacturer or warehouse to the store or to your home can undo all the hard effort that went into making the product in the first place. If you had any idea just how they get the fish oil in the first place......you don't wanna know.
Lar
poster:Larry Hoover
thread:453064
URL: http://www.dr-bob.org/babble/alter/20050131/msgs/457641.html