Crustaceans, taste

Derby, C. D., Single unit electrophysiological recordings from crustacean chemoreceptor neurons, in Experimental Biology of Taste and Olfaction Current Techniques and Protocols, Spielman, A. I. and Brand, J. G., Eds., CRC Press, Boca Raton, FL, 1995, 241. 

In Japan, a wide variety of marine products, such as algae, molluscs, crustaceans, echinoderms, and fish have been consumed with relish from olden times. These food habits have stimulated many studies on the extractive components which may contribute to the taste of these products. Several comprehensive reviews on the subject are available (l-8 ) In order to avoid overlapping with them, special references are made in this review to those components whose roles in producing the taste of fish and shellfish have been examined organoleptically. 

From these results and from the free amino acid compositions of the extracts, they regarded amino acids, chiefly glutamic acid and glycine, as the main contributors to the taste of these crustaceans. 

The flavor of fish and seafoods is composed of taste-active low molecular-weight extractives and aroma-active compounds. The taste-active compoimds are more abundant in the tissues of mollusks and crustaceans than fish. The most important non-volatile taste components are fi-ee amino acids, nucleotides, inorganic salts and quaternary ammonia bases. Alcohols, aldehydes, ketones, furans, nitrogen-containing compounds, sulfur-containing compounds, hydrocarbons, esters and phenols are the most important volatiles is shellfish. Alkyl pyrazines and sulfur-containing compounds are important contributors to the cooked aroma of crustaceans. Furans pyrazines, and Lactones have been found in heat-treated seafoods. Dimethyl disulfide, dimethyl trisulfide, heterocyclic sulfiir-containing compounds (alkylthiophenes) have been found in most thermally treated crustaceans like prawn, crab, oyster, crayfish and shrimp (52). 

The evolutionary transition from water to land has resulted in an expansion of the chemoreceptor genes, most likely in response to the multitude of airborne odorants (Bargmann 2006). Organisms that frequently change between aquatic and terrestrial environments (e.g., amphibians) appear to have chemosensory systems for perception of both water-soluble as well as volatile odorants (Freitag et al. 1995). Soluble and volatile chemicals can also be perceived by aquatic and terrestrial crustaceans, respectively (e.g., Hansson et al., Chap. 8). However, at least in terrestrial peracarids, taste reception of odorants appears to be mediated by liquids (Seelinger 1983 Holdich 1984), just as food-smelling of terrestrial mammals under water is mediated by air bubbles (Catania 2006). 

The matching dichotomy of sensilla construction and neuroanatomical organization of sensory neuropils suggests that in crustaceans chemical information is received and processed in two fundamentally different modes. One mode is Olfaction which we define as chemoreception mediated by the aesthetasc - OL pathway the second mode is Distributed Chemoreception, which we define as chemoreception mediated by bimodal sensilla on all appendages and the associated striated neuropils that serve as local motor centers. Distributed chemoreception not only comprises taste, which we define as contact chemoreception in the context of... 

Upon returning to our home base we analyzed the more detailed structure of the olfactory organs of B. latro. The aesthetascs could be divided into at least two types, where one is more prevalent towards the tip of the antenna, and displays what might be a terminal pore. The placement and the possible pore could indicate a function in taste perception. The major part of the aesthetascs was uniformly scale-like without terminal pore. In fact, no pores at all could be observed, not even the minute cuticular pores observed in almost all insect olfactory sensilla. We have so far not been able to elucidate how molecules in gas phase enter the inside of the B. latro aesthetascs. Each hair was shown to contain a very large number of olfactory receptor neurons, not only similar to what has been found in other crustaceans, but also in e.g., honeybees and locusts (Hansson et al. 1996 Ochieng et al. 1998). 

Blue crabs are known to all who frequent shallow waters along the east coast of North America. Their abundance and tasty meat have made them a major commercial fishery for hundreds of years. Lifestyles of people, even cultures, have been defined by them, as chronicled in William Warner s book, Beautiful Swimmers Watermen, Crabs and the Chesapeake Bay. In fact, the blue crab s scientific name, Callinectes sapidus, given in 1896 by Dr. Mary Jane Rathbun, at the time one of the foremost authorities on crustacean systematics, means good-tasting beautiful swimmer. That they are, but they are much more, as we hope we convey in this chapter. 

Extracts of shrimps and other crustaceans are desirable as taste additives in foods that are to have shellfish character. In addition, a hydrolysate from fish myofibrils has been claimed to have a synergistic effect with antioxidants (Hatate et al., 1990). This has also been reported for a mixture of amino acids from krill (Seher and Lbschner, 1986). In one case the single amino acid, proline, has been used as an antioxidant in fish oil (Revankar, 1974). The precise mechanisms for the antioxidative or synergistic actions are not known. 

Trimethylamine oxide, (CH3)jN+0, an onium salt found in marine but never in fresh-water fishes. Rich sources are eephalo-pods and crustaceans, the muscle of the lobster containing about 0 3 per cent. The oxide is soluble, non-toxic and almost neutral, and is an important excretory form of nitrogen. Among the elasmobranchs it serves in the maintenance of fluid equilibrium, and is responsible for 20-25 per cent, of the total osmotic pressure of the blood. It is rapidly decomposed by post-mortem autolytic and bacterial changes, and the liberated trimethylamine, (CH3)jN, characterises the odour and taste of stale marine fish. 

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