Attempts To Use Seafood Flavor And Texture Attributes To Classify Fish

Due to a greatly expanded U.S. fishery, the American seafood marketplace contains a variety of new commercially harvested fish with little name familiarity, which has created a minor identity crisis in the industry and for the consumer. Although the National Marine Fisheries Service of the U.S. Department of Commerce (NMFS), the American Fisheries Society, and the International Congress of Zoology maintain scientific names of glossaries of common fish names, these are generally unsuited for use in market identification. To make matters worse, common names for fish species used in the United States contain little or no useful information for the consumer (139). As an example of the problem, some fish have many common names (as many as 5) from as many different locations, and many popular commercial fish have several common names, such king salmon which is also known as chinook, blackmouth, and spring salmon. Also, commonly used names in one region of the United States may be misleading in another, for example, the fish known as "snapper" along the Pacific coast is a species of rockfish (Sebastes spp.), not the acceptable Lutjanidae spp. from the Gulf of Mexico and Caribbean that the Food and Drug Administration has officially designated as snapper. In other cases, names may be unattractive or pejorative or may reflect ethnic slurs or epithets (eg, ratfish, hagfish, wolffish, jewfish, etc). As a result, consumers can learn little about the edibility characteristics of a product from its name, thus a large variety of seafoods remain effectively unavailable to them. Faced with a bewildering array of common names, it is not surprising that consumers confine their purchases to a few familiar items rather than deal with the unknown.

Because the American consumer was perceived as resisting the purchase of new seafoods that appeared in the marketplace because of a lack of information about what they taste like, NMFS launched a research project to determine the feasibility of developing a national nomenclature system that would group fish species according to their edibility characteristics (flavor and texture). It was felt that both processors and retailers could employ such a system to group together fish that share the same edibility characteristics so that consumers, both new and experi enced, would be able to consistently and knowledgeably select their seafood. The system could work much like our classification of wines in the United States (ie, Chablis, Burgundy, claret, etc). Each of these wine classifications can contain one or more specific grape varietals, for example, claret can be made from Cabernet sauvignon, Mer-lot, or both.

It is a common human trait to classify and group that which interests us. For example, we readily group foods based on ethnic origin (eg, Italian, Mexican, Chinese, Japanese); we even break down the cuisines of a single country (eg, French/Provencal, Chinese/Szechuan, American/ Southern, Mexican/"Tex-Mex"). The classification of seafoods is no exception. It is quite common to hear a buyer in the fish market ask, "What is this fish like for eating?" Questions of this type are not at all unreasonable considering the large number of fish species that crowd both Western and Asian marketplaces (more than 1,000 worldwide, 500 in the U.S. alone). Inevitably, the answers to such questions will involve one or more flavor attributes (eg, sweet, mild, strong, etc). Clearly, the flavor of a fish species is one of the most important criteria that the consumer exercises when he or she purchases seafood.

It should be clear that the various chemical compounds that impart characteristic flavors and odors to a particular species of fish are many and complex. Despite the efforts of scientists, certainly as detailed in this chapter, the relationships of specific chemical compounds and observed flavors and odors are yet to be completely understood. To date, the marketplace must ultimately rely on the consumer to determine what a fish "should be." However, to be "knowledgeable" about fish has, in recent years, become increasingly more difficult because of a large increase in the number of fish species and products finding their way into the marketplace (136). Demands on the consumer's discriminatory abilities will be increased as even more fish species are introduced into the marketplace, both in the United States and elsewhere. This increase is due to a variety of political, economic, social, and health reasons. Economic factors are perhaps the easiest to identify. In the past, fishermen, particularly those of developed countries, would keep only the most desirable fish, such as halibut, salmon, and cod, in the catch and return the less-desirable species, the so-called "by-catch," to the sea. However, with increased global demand for fishery products as well as improved (and sometimes costlier) fishing technology and processing methods, many species offish in the "by-catch" heretofore not always utilized are now harvested and processed into edible products.

To help resolve these problems of nomenclature, NMFS, in its role of providing technical and marketing assistance to the fishery industry, organized and coordinated a program to attempt to clarify existing marketing names and provide improved procedures for establishing a uniform seafood nomenclature. As part of this project, NMFS funded a study that eventually involved elements of the U.S. Army Research Laboratories at Natick, Massachusetts (NLABS); the University of Massachusetts; Arthur D. Little Co.; and NMFS laboratories in Gloucester, Massachusetts; Charleston, South Carolina; and Seattle, Washington. As envisioned by NMFS and its collaborators, the system would be based on similarities in edibility characteristics among the various fish species produced by U.S. commercial fisheries. The system would enable consumers and the fishing industry to make informed choices among species (familiar and unfamiliar) by providing comparative sensory data consumers need to select a desired texture, flavor, and so on, of fish (140,141).

Although sensory analyses are commonly used in fisheries research, quality control, and inspection (142), it was recognized at the beginning that there was no comprehensive set of sensory terms available that was meaningful and useful to consumers for making comparisons between different species (141). In addition, because sensory comparisons were to be a part of this project, there was a need for a reliable scaling method that permitted the development of quantifiable numeric sensory profiles that could be statistically manipulated into valid groups. This work included research in methods of cooking; sensory panel techniques; and the development of sensory attributes to describe fish samples, including the development of descriptive terms and selection of a psychophysical method for scaling the magnitude of sensory attributes. Ultimately, a complex protocol was developed for classifying fish based on edibility characteristics, including texture, flavor, and chemical compositional attributes. Although this edibility profile involved both flavor and texture attributes, for purposes of this chapter only the work with flavor will be discussed. More detail will be given to this work because we feel that the sensory methods combined with statistical methods, such as cluster analysis, and the descriptors developed for this project have useful application to other areas of seafood technology.

Sensory Panels

Because of the consumer-oriented nature of this project, a comprehensive list of sensory attributes that could be applied to a wide range of edible fish species (141) was developed. This was achieved through the use of both extensive consumer and trained-taste panel assessments. The descriptive sensory analysis of aroma, flavor-by-mouth, and aftertaste attributes of cooked fish muscle was performed by the Natick flavor profile panel using the Arthur D. Little Flavor Profile Method (143,144). From these panels and related activities, a list of descriptive terms that was applicable to the description of the edibility characteristics of fish was generated through the use of statistical methods that were able to identify attributes that best discriminated among the various species of fish. Concomitantly, the researchers had to select a reliable scaling method for the tasters to use to describe the magnitude of the sensory attributes. The method selected was based on a 7-point category scale of intensity where 1 = slight, 4 = moderate, and 7 = extreme. Complete details of the procedures used to develop the scalar method can be found in Kapsalis (140), Cardello et al. (145), and Sawyer et al. (146). As the result of extensive testing and winnowing, a list of flavor descriptors emerged (Table 4).

The resulting system was tested by applying the method to a model system of 17 species of North Atlantic fish. Among the species of fish tested were Atlantic whiting

Table 4. Sixteen Flavor Attributes Identified by Consumers and Trained Panelists as Important to the Characterization of Fish

Flavor attributes

Overall flavor intensity" Delicate or fresh fish Heavy or gamey fish" Fish (old fish) Sweet

Briny, salty"

Sour"

Seaweed

Bitter

Fish oil"

Buttery

Nutty

Musty

Ammonia

Metallic

Shellfish"

"These flavor attributes were found to be significant discriminators on the basis of stepwise discriminant analysis.

(Merluccius bilinearis), Atlantic mackerel (Scomber scom-brus), monkfish (goosefish) (Lophius americanus), Atlantic pollock (Pollachius virens), and others. Once completed, the results of the texture and flavor panel analyses were compiled as mean texture attributes and consensus ratings for flavor attributes of the 17 species of fish (139). From the compiled data, it was possible to compare and contrast the various species using a composite profile such as that shown in Figure 1 (137), where weakfish and cusk are contrasted. The model was further analyzed to identify groups of fish with similar characteristics using cluster analysis (147). The tree diagram in Figure 2 (140) shows the results of cluster analysis of the combined sensory data. Although limited in scope by the low number of fish evaluated, the purpose of the tree is to show the order of combination of the species. Pollock and tilefish, located opposite number 1 on the left side of the diagram, are paired

Gaminess Fish oil Earth iness Shellfish Mouth dryness Sourness Salty-briney Fresh fish

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