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  • The Spoilage of Fish and Its Preservation by Chilling

    BY G . A . REAY AND J . M . SHEWAN Tony Reeearch Station. Aberdeen. Scotland

    CONTENTS

    f i w I . Introduction . . . . . . . . . . . . . . . . . . . . 344

    I1 . General Deacription of the Spoilage of Fish . . . . . . . . . . 395 1 . Introduction . . . . . . . . . . . . . . . . . . 346 2 . Types of Fish and Fishery . . . . . . . . . . . . . . 348 3 . Organoleptic Characteristica of Fresh and Spoiling Fish . . . . . 348

    I11 . The Bacteriology of Fresh and Spoiling Fish . . . . . . . . . . ags 1 . The FLOra of Freshly-Caught Fish . . . . . . . . . . . 348 2 . The Flora of Spoiling Fiah . . . . . . . . . . . . . . 362

    .151 5 . . . . . 366

    5 . The Routea of Bacterial Attack . . . . . . . . . . . . 367 6 . The Influence of Temperature and pH on the Bacteria of Fish . . 368

    IV . The Biochemietry of Spoilage . . . . . . . . . . . . . . 381 1 . Immediate PoetMortem Changes . . . . . . . . . . 381

    a . Changes in the Glycogen and Lactic Acid Content. and pH of Fish Muscle . . . . . . . . . . . . . . . . . . 362

    b . Rigor Mortis . . . . . . . . . . . . . . . . 364 2 . Biochemical Spoilage Changea . . . . . . . . . . . . . 387

    a . Introduction . . . . . . . . . . . . . . . . . 367 b . Trimethylamine Oxide . . . . . . . . . . . . . 387 c . The Trimethylamine Oxide Reduction Phase of Spoilage 388 d . The Formation of Dimethylamine . . . . . . . . . . 371 e . Proteolysis . . . . . . . . . . . . . . . . . 371 f . Changes in pH . . . . . . . . . . . . . . . . 312 g . The Spoilage of Fat . . . . . . . . . . . . . . 813

    3 . The Comparative Biochemical Activity of the Bacterial Groups 4 . The Increase in Bacterial Population During Spoilage

    . .

    . . .

    V . The Estimation of the Quality of Fish . . . . . . . . . . . 373 373 376

    a . Chemical Teets . . . . . . . . . . . . . . . . 376 (1) The trimethylamine and dimethylamine teats . . . . 376 (2) The eurfaoe pH test . . . . . . . . . . . . 381 (3) The titration teat . . . . . . . . . . . . . 382 (4) Miscellaneous teate . . . . . . . . . . . . 382

    b . Bacteriological . teets . . . . . . . . . . . . . . 383 3.Conclusion. . . . . . . . . . . . . . . . . . . 383

    . . . . . . . 384 384

    a . Introduotion . . . . . . . . . . . . . . . . . 384 h . Chilling . . . . . . . . . . . . . . . . . . 3M c . Handling and Stowage . . . . . . . . . . . . . 386

    . . . 1 . General Consideration of Organoleptic and Objective Testing 2 . Objective T e d of Quality . . . . . . . . . . . . . .

    VI . The Practical Control of the Quality of Wet Fish . . . . . . 1 . The Handling and Stowage of Dememl Fish at Sea

    343

  • 344 Q. A. W A Y AND J . M. SHEWAN

    2. The Handling and Stowage of Pelagic Fish . . . . . . . . . 387 3. Handling, Transport and Dietribution on Land . . . . . . . a88 4. Conclusion . . . . . . . . . . . . . . . . . . . 389

    VII. General Conclusion . . . . . . . . . . . . . . . . . . aa0 References . . . . . . . . . . . . . . . . . . . . 393

    I. INTRODUCTION

    The annual World production of fish was estimated for representative prewar years to have been about 16.5 million tons (Sandberg, 1944). Fish is therefore a highly important source of food and research has clearly established its high nutritional quality.

    Fish, however, is one of the most perishable of foods, so that its trans- port and wide distribution in acceptable condition presents a preservation problem of no small magnitude. Fishing grounds are frequently far dis- tant from home ports and these in turn from the main centers of con- sumption. A number of countries, e.g., Canada, Iceland, Newfoundland, and Norway, in which fishing is one of the principal industries, produce much more fish than can be consumed a t home, necessitating export over long distances. Many important species are caught in abundance during a relatively short season, and this large annual supply must be distributed more evenly over the year.

    Man discovered in very early times, possibly by chance, how to pre- serve locally caught fish for long periods by salting, drying and smok- ing, or combinations of these; a major proportion of the worlds catch is still preserved by these means. In the more highly developed coun- tries, however, where standards of living have been steadily rising during the last century the demand for such crude fish products has been stead- ily falling, and increasing preference has been shown for fish that has re- tained to a much greater extent the flavor, odor, appearance, and texture of the freshly caught fish. Hence the growing demand for wet, i.e., un- processed, fish, even though frequently not of the freshest quality; or for very lightly cured fish; or for fish processed by modern methods of frees- ing and canning, which preserve the original characteristics of the fresh fish to a high degree. The primary problem of the industry in the more developed countries, therefore, is to retain the quality of freshly caught fish a t sea or on land, in the wet or unprocessed condition, either for consumption in thiR condition or for processing by acceptable ninriem methods.

    Historically, the problem presented itself acutely during the last quar- ter of the nineteenth century with the urge to tap rieher, more distant fishing grounds in order to meet the needs of increasing industrial popu- lations. The introduction of steam propulsion and of more efficient

  • THE SPOILAGE OF F18H AND Im YREtiEHVATlON BY CHILLINQ 346

    catching methods and gear permitted more abundant catching and a wider radius of fishing; and the preservdon of the catches in edible con- dition was accomplished by eviscerating the fish and chilling them in crushed ice-in natural ice to begin with, but later largely in artificial ice. By these methods an enormous increase in fish supplies has been brought about during the present century in the countries bordering the northern oceans. A wider distribution of wet fish inland has been helped by better, speedier transport. However, in recent years as nearer grounds have been overfished and still further ones exploited, the limi- tations of chilling as a preservative of quality have become increasingly apparent. Much thought is being given to the possibilities of improving this method of preservation, or of supplanting i t by processing, e.g., freezing, or where tipproprittte, canning, a t sea.

    It is the purpose of this paper to review existing scientific a i d technical data concerning the various factors affecting the spoilage of wet fish and the retention of quality by chilling, and to indicate where our knowl- edge is insufficient and further research is required, and finally to suggest possibilities of improving current industrial practice in handling and stor- age.

    11. GENERAL DWCRIPTIIJN OF THE SPOILAGE OF FISH

    1. Introduction The spoilage of fish, as of other foods, is usually stated to be effected

    by autolysis, oxidation, and bacterial activity. All the existing evidence goes to show that the last is apparently by far the most important factor in producing the more striking and undesirable alterations in the flavor, odor, and appearance of fish, although in fatty fish under certain condi- tions unacceptable oxidative rancidity may precede bacterial deteriora- tion. It may well be that autolysis prepares the way for and assists the bacterial attack, but i t has not been clearly demonstrated that i t does so in whole fish under the normal conditions of handling and stowage, nor would i t be easy to demonstrate. On the other hand, it seems very prob- able that the softening of the flesh as it spoils is largely autolytic in origin, although bacterial enzymes no doubt also contribute once the flesh has become grossly contaminated.

    The present paper will be largely concerned with spoilage as effected by bacteria. In spoilage, there is interaction between bacteria on the one hand and the chemical and physical composition of the fish on the other. The kind and numbers of bacteria originally on the fish and subsequently picked up during handling and distribution are subject to a variety of ecological and seasonal factors and perhaps vary also with the species of

  • 346 Q. A. BEAY AND J. M. SHEWAN

    fish. On the other hand, the physical and chemical nature of fish may vary with species, season, state of maturity, age, nutrition, and environ- ment. Moreover, the course of spoilage in any instance is subject to the influence of environmental factors, particularly temperature. These con- siderations serve to show how extremely complex the bacterial spoilage of fish is, and it should be said at once that research has gone only a short way to resolving the complexity.

    Before attempting to discuss the bacteriology and biochemistry of spoilage in some detail, a broad account will be given of the spoilage of fish as it is normally perceived by the senses.

    8. Types of Fish and Fiahgl It is first of all advisable to note that marine fishes are conveniently

    and appropriately considered from many points of view as falling into two broadly different classes, demersal and pelagic.

    The demersal fishes (e.g., cod and allied species, the flat fiahes, and the dogfish, skates, etc.) , the flesh of which is relatively nonfatty (see review of the chemical composition of fish by Reay et aZ., 1943), are generally caught by trawl net or line on or near the sea bottom, over a relatively wide geographical range in relation to the home port. These fish are in consequence gutted and washed a t aea soon after catching and are stowed in ice for most of the time elapsing, a t sea and on land, between catching and consumption or processing.

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