Fishy fresh

When someone buys fresh fish, they often smell the fish to test for freshness—the fresher the fish, the less fishy the smell. What is the source of the fishy odor ... 

The development of both desirable and undesirable fishy flavors has long-been a concern to the seafood and fishery Industry (1-6). Oxidative processes occurring through enzymic and nonenzymlc mechanisms Initiate hydroperoxide formation In fish lipid systems that are responsible for the formation of the short chain carbonyls and alcohols which exhibit distinct flsh-llke flavors and aromas. Because the generation of fresh fish aroma compounds Involves some of the same polyunsaturated fatty acid precursors and oxidative pathways as autoxldatlon. It has been a tedious task to differentiate the mechanisms and aroma compounds... 

EFA supplements can come as gel capsules or in liquid form. Even the experts don t agree on the optimum ratio of omega-6 fatty acids to omega-3s, but look for a ratio between 4 1 and 1 1, and always check for freshness. The supplements should be refrigerated, and the omega-3s last for only about six months, so if they look like they ve been collecting dust on the shelves of your health food store, you might be better off with another product. Liquid supplements should not smell rancid or fishy, even if they are from a fish source. 

The definition of oxidized fish oil-like aromas still leave fresh fish aromas undefined. Various freshly harvested fish have distinguishing aromas, but they also are characterized by a common plant-like, seaweed-like aroma. Thus, compounds and reaction pathways different from random autoxidation appear likely and reasonable. Even conflicting descriptions of fishy odors, i.e., including roles for volatile amines (2 19) and sulfur compounds (20-22), can be accommodated by the hypothesis that previously unrecognized biochemical reactions yield characterizing fresh fish aromas. These premises led to investigations (23-26) which have resulted in the identification of a group of enzymically-derived volatile aroma compounds that contribute fresh, plant-like aromas to freshly harvested fish (Table I). 

When mushroom homogenates were incubated with surimi, enhanced plant-like aromas somewhat reminiscent of oysters were produced, and this treatment also resulted In the masking of some of the fish-like aromas of the surimi. Cucumber homogenates developed strong cucumber, cardboard-like aromas which appear to be contributed principally by 2-nonenal and 2,6-nonadienal. As a result, the cucumber homogenates caused undesirable and unbalanced aromas that did not suppress unpleasant fishiness. Watermelon fruit extracts behaved similarly, and also provided unbalanced sweet aromas to surimi. Tests to date have been limited to short-term incubations of crude enzyme preparations with surimi. Further exploration of more purified and controlled plant-based flavor-generating enzyme systems for the production of fresh seafood-like aromas, and especially those for the eight-carbon volatile aroma compounds, appear warrented. 

Fresh fish doesn t smell fishy at all. It s only when proteins and amino acids in fish start to break down, releasing stinky nitrogen and sulfur compounds, that the funk sets in. There are a few reasons that this sort of smelly decay is more common with fish than with chicken, beef, or pork. Fish frequently eat other fish, so their digestive systems contains enzymes that can break down the proteins found in fish. So if some of these enzymes leak out, or if you re slow to gut your fish, those enzymes will go to work...on its own flesh. Fish also generally have higher levels of unsaturated fats, which are less stable than saturated fats to oxidation. Acids, like lemon juice, can slow the enzymes down, and convert the amines into less odorous ammonium salts, which is probably why we re all used to squeezing a lemon wedge on fish. 

Definition Fixed oil expressed from fresh livers of Gadus morrhua and other species of codfish, contg. vitamins A and D, omega 3 fatty acid Properties Amber thin oily liq., si. fishy odor and taste sol. in ether, chloroform, ethyl acetate, carbon disulfide, petroleum ether si. sol. in alcohol negligible sol. in water dens. 0.918-0.927 iodine no. 145-180 sapon. no. 180-192 ref. index 1.4705-1.4745... 

Kummerow et al. (1948) found that the feeding of highly unsaturated fatty acids was detrimental to fat stability of eviscerated frozen turkeys, as determined both by peroxide values on the extracted skin fat and also by organoleptic tests on the cooked carcass. Klose et al. (1951) observed fishy flavors in roasted turkeys fed linseed oil as well as fish oils. The fishy flavors in this case were present in the fresh roasted turkeys as well as in those cooked after being stored in the freezer. Peroxide values of birds fed linseed oil increased very rapidly in freezer storage. 

The final means by which MO can produce OF in foods is the most common. That is from growth in the food and contanunation with metabolic products. Fresh fish [17] and dairy prodncts [129] are two foods that are very susceptible to OF from nuCTobial sources. Fresh fish is generally considered to have very little odor. However, if fish is stored above freezing tanperatures, the fish develops a fishy OF initially that later becomes pntrid and foul in character. Fish is particularly susceptible to nuCTobial growth since the fish muscle has substantial soluble material and cells tend to lyse once the fish has been killed. The fish muscle provides a rather ideal growth medium for MO. 

The fishy and greasy off-flavour appearing in long-term refrigerated storage of fish is almost entirely caused by lipid oxidation products that are present in larger quantities than in fresh fish. The important components are mainly (Z)-hex-3-enal, (Z)-hept-... 

The fishy aroma of seafood is incorrectly attributed to trimethyl amine. Flavor formation in fresh and saltwater fish results from complex enzymatic, oxidative, and microbial reactions of n-3 polyunsaturated fatty acid precursors (e.g., eicosapentaenoic acid) (69,70). Hence, fish flavor is mostly composed of non-characterizing planty or melon-like aromas from lipid-derived unsaturated carbonyl compounds. Examples are (Z)-l,5-octadien-3-one ( geranium-like ) in boiled cod (71) and (7i,Z)-2,6-nonadienal ( cucumber-like ) in boiled trout (72). 

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