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The main edible portion of a marine animal is composed of the largest muscles of the body. However, many other parts are also used as food, especially the skin, liver, milt, roe, the fins of shark, and the alimentary tract of squid. The hydration of proteins is responsible for the rheological properties and juiciness of muscle foods. In tables of food composition, the content of proteins refers usually to the crude protein. Among the sarcoplasmic enzymes influencing the quality of fish as food are mainly the enzymes of the glycolytic pathway and the hydrolytic enzymes of the lysosomes. The nutritive and commercial value of various fish and marine invertebrates depends on the structure of the flesh and other edible parts, on the proportions of these parts in the total mass of the specimen, on the chemical composition of the meat, gonads, liver, etc., and on factors related to fishing and handling procedures.

The postharvest biochemical and microbial changes in fish tissues depend very sigificantly upon the factors which effect the concentration of substrates and metabolites in the tissues of the live fish, the activity of the endogenous enzymes, the microbial contamination, and the conditions after catching. The biochemical post-mortem changes, involving the main chemical constituents of the tissues, bring about various structural alterations in the tissues, including rigor mortis, and different degrees of disintegration of the muscle ultrastructure. The biochemical state of the postrigor muscles is different from that of the prerigor flesh. The time after which the onset of rigor is noticeable, the degree of change in the rheological properties of the fish body, and the duration of the stiff condition depend upon factors influencing the biochemical state of the muscles at the time of death and on the rate of post-mortem processes.

The quality indices of Atlantic mackerel, hot smoked at core temperature not exceeding 60°C, containing 14–27 g salt and 580–670 g water per kg meat, was determined just after smoking and during storage. The aerobic plate count after smoking, chilling and packing in cardboard boxes was 0–12 cfu/25 cm2of the skin of the smoked fish and 10–240 cfu/g of flesh. It was 1.9 log cycle lower than that in the frozen raw material. At 2°C, the bacterial count on the fish surface and in the meat remained unchanged for at least 3 wk. At 8°C after 14 d, the cfu in the meat of smoked fish ranged from 1.8×102to 1.6×107/g. The total count on the skin and just under the skin did not increase up to 21 d at 2 and 8°C. There was no statistically significant difference between the mean values of all evaluated sensory attributes of the smoked fish stored up to 2 wk at 2 and 8°C. These results regard products from a smoking plant of very high hygienic standard, fulfilling all EC requirements, with quality assurance system based on HACCP.

The catalytic properties of chitin deacetylase from Mucor rouxii were studied with the aim of using the results for control of the properties of chitosan prepared by enzymatic deacetylation. A crude deacetylase extract from the mycelium of Mucor rouxii exhibited maximal activity at pH 5.8 with both water-soluble and acid-soluble chitosan. The extracellular enzyme of the culture medium exhibited maximal activity at pH 4.8. The deacetylase in the crude extract was stable over the pH range of 4.1-8.9 at 25C, retaining 85-100% of maximal activity at 40C. The extract was most active towards acid-soluble chitoson at 50C and pH 5.8. Chitin deacetylase was stable to 40C when incubated without substrate, with 85% of the activity retained at 50C. Ca 2+ , Mn 2+ , and Zn 2+ had no effect on activity, while EDTA, Fe 2+ , and Fe 3+ caused partial inhibition in extracts incubated without substrate for 1 h at 25C and pH 5.8. The deacetylase in the mycelial extract and in the culture medium was slightly activated by Co 2+ . The differences in temperature optima and thermal stability of deacetylase and hydrolytic enzymes can be used for controlling the degree of hydrolysis of chitosan, while the difference in pH stability has been used for prepurification, resulting in 3-fold increase in specific activity of deacetylase.

Muscle proteases active at neutral and alkaline pH's include calcium-activated neutral proteases, heat-activated thiol proteases, serine proteases, and metallo-proteases. They participate to different extents in postmortem degradation offish muscle myofibrillar and scaffold proteins. Their activity in fish muscle is varied and depends on location in the muscle, the life cycle of the fish, the presence of endogenous activators and inhibitors, pH, and temperature. Recent studies indicate that neutral and alkaline proteases have more impact on the postmortem deterioration in quality of fish muscles than the cathepsins active at acid pH. Significant quality losses are caused by enzymatic collagen degradation in raw tissues and by heat-activated enzymes in fish gels.

The Nomenclature and Structure of Lipids David S. Nichols, Timothy B. Jordan, and Neil Kerr Chemical and Physical Properties of Lipids David S. Nichols, Timothy B. Jordan, and Neil Kerr Principles of Lipid Analysis David S. Nichols, Timothy B. Jordan, and Neil Kerr Lipids and Food Quality Anna Kolakowska and Zdzislaw E. Sikorski Lipids in Food Structure Wioletta Blaszczak and Jozef Fornal Phospholipids Jan Pokorny and Stefan Schmidt Cholesterol and Phytosterols Erwin Wasowicz and Magdalena Rudzin'ska Lipophilic Vitamins Malgorzata Nogala-Kalucka Lipid Oxidation in Food Systems Grzegorz Bartosz and Anna Kolakowska Antioxidants Anna Kolakowska and Grzegorz Bartosz Dietary Lipids and Coronary Heart Disease Zdzislaw Florian Forycki Role of Lipids in Children's Health and Development Grazyna Sikorska-Wis'niewska Lipids and the Human Vision Pawel Lipowski Plant Lipids and Oils Jan Pokorny and Stefan Schmidt Fish Lipids Anna Kolakowska Milk Lipids Michael H. Tunick The Role of Lipids in Meat Zdzislaw E. Sikorski and Izabela Sinkiewicz Egg Lipids Waldemar Ternes and Astrid M. Drotleff Modified Triacylglycerols and Fat Replacers Marek Adamczak and Wlodzimierz Bednarski Lipids with Special Biological and Physicochemical Activities Marek Adamczak and Wlodzimierz Bednarski Frying Fats Dimitrios Boskou Lipid-Protein and Lipid-Saccharide Interactions Jan Pokorny, Anna Kolakowska, and Grzegorz Bienkiewicz Contaminants of Oils: Analytical Aspects Fahri Yemiscioglu, Aytac Saygin Gumuskesen, Semih Otles, and Yildiz Karaibrahimoglu

The liver extract of squid Illex argentinus has a proteolytic activity at pH 2–8, with optimum at pH 2.6–3.1. At pH 6 the enzymes retain about 30 and 55% of the maximum proteolytic activity towards hemoglobin and casein, respectively. In squid mantle meat treated with the extract 24 h at 4C and 20C, the sarcoplasmic and myofibrillar proteins were hydrolyzed to low molecular fractions, as was shown by SDS-PAGE. Soaking isolated collagen fibers in the liver extract resulted after 24 h in almost complete solubilization of the fibers in buffered SDS/urea solutions. The solubilized product contained only low molecular weight components. A significant hydrolysis of the proteins in the squid mantle, treated with the liver extract at 20 or 4C, was accompanied by a decrease in toughness of the cooked product by about 65 and 40%, respectively, as compared to the toughness of untreated cooked samples. Cooking of the mantle directly in the liver extract had practically no tenderizing effect.

Each chapter ends with a section of references. Preface FOOD COMPONENTS AND THEIR ROLE IN FOOD QUALITY - The Main Food Components - The Quality of Foods - The Functional Properties of Food Components - The Role of Chemistry and Processing Factors WATER AND FOOD QUALITY - Introduction - Structure and Properties of Water - Water in Food - Water Supply, Quality, and Disposal MINERAL COMPONENTS - The and Role of Minerals in Foods - Interaction with Dietary Components - Role in Food Processing - The Effect of Storage and Processing on the Mineral Components in Foods - The Chemical Nature of Toxicity of Some Mineral Food Components SACCHARIDES - Natural Food Carbohydrates, Occurrence, Role, and Applications - Carbohydrate Structure - Carbohydrate Chirality - Carbohydrate Reactivity - Functional Properties of Carbohydrates - Biodegradable Plastics LIPIDS - Part I: Chemical and Functional Properties - Part II: The Effect of Refining and Hardening on the Composition of Fats PROTEINS - The Chemical Structure and Properties - The Functional Properties - Changes Due to Processing - Enzymatic Changes - Chemical Modifications - Use of Proteins as Functional Components in Foods - Edible Coatings RHEOLOGICAL PROPERTIES OF FOOD SYSTEMS - Introduction - The Flow Properties of Liquid and Semi-Solid Food System - The Effect of Composition and Processing Parameters on the Rheological Behavior of Food Systems - The Importance of the Rheological Properties of Foods for Process Design and Control FOOD COLORANTS - Introduction - Natural Pigments - Synthetic Organic Colors FLAVOR COMPOUNDS - Sources of Flavors in Foods - Molecular Structure and Odor of Flavor Compounds - Changes in Flavor during Food Storage and Processing - Use of Flavors in Food Industry MAIN FUNCTIONAL FOOD ADDITIVES - Introduction - Classification - Preservatives - Antioxidants - Stabilizers, Emulsifiers, and Thickening Agents - Clarifying Agents and Film Formers - Flavorings, Colorants, and Sweeteners FOOD SAFETY - Introduction - Consumer Attitudes to the Food Safety Problem - Tests to Determine Food Safety - Food Safety Concerns - Risk/Benefit as It Applies to Food - Nutritional Evaluation of Food Processing MUTAGENIC AND CARCINOGENIC COMPONENTS IN FOODS - Introduction - The Role of Mutagens in Carincogenesis - Metabolic Activation and Formation of DNA Adducts by Food Mutagens and Carcinogens - Tests for Mutagenicity and Carcinogenic Properties of Food Components - Foodborne Mutagens and Carcinogens - Anticarcinogenic Food Components Index 42 figures, 28 tables ISBN: 1 -56676 -464 -5 Year: 1997 Number of pages: 301 Dimensions: 6 " x 9" Cover type: hardcover $149.95 Authors - Agnieszka Bartoszek, Ph.D., Department of Biochemistry, Technical University of Gdansk, Poland - Barbara Cybulska, Ph.D., Department of Biochemistry, Technical University of Gdansk, Poland - Peter Doe, Ph.D., Professor, Department of Engineering, University of Tasmania, Australia - Tadeusz S. Matuszek, Ph.D., Department of Food Engineering, University of Gdansk, Poland - Julie Miller Jones, Ph.D., Professor, Department of Home Economics, College of St. Catherine, USA - Michael Nabrzyski, Ph.D., D.Sc., Professor, Department of Bromatology, Medical Academy of Gdansk, Poland - Bonnie Sun Pan, Ph.D., Professor, Department of Marine Food Science, National Taiwan Ocean University - Adriaan Rutter, Ph.D., Professor, Department of the Science of Food of Animal Origin, Utrecht University, The Netherlands - Jan Sawicki, Ph.D., Department of Chemistry and Technology of Fats, Technical University of Gdansk, Poland - Zdzislaw E. Sikorski, Ph.D., D.Sc., Professor, Department of Food Preservation, Technical University of Gdansk, Poland - Bartlomiej Slusarski, M.Sc., Department of Technology of Lipids and Detergents, Technical University of Gdansk, Poland - Piotr Tomasik, Ph.D., D.Sc., Professor, Department of Chemistry, Academy of Agriculture, Poland - Alphons G. J. Voragen, Ph.D., Professor, Utrecht University, The Netherlands - Jadwiga Wilska-Jeszka, Ph.D., D.Sc., Professor emeritus, Institute of Technical Biochemistry, Technical University of Lodz, Poland - Chung-May Wu, Ph.D., Senior Scientist, Food Research and Development Institute, Taiwan

Trimethylamine oxide (TMAO) in the muscle of squid may be reduced by endogenous and bacterial enzymes to trimethylamine and demethylated in enzymatic or chemical reactions to dimethylamine (DMA) and formaldehyde (FA). The rate of TMAO degradation in heated Baltic cod and in squid extract and flesh, as well as the effect of FA generated in the tissues on the texture of cooked squid were investigated. The content of DMA in uncooked frozen stored mantle of 51 Illex argentinus, from three different shipments, was 88–452 μmoles/100 g meat. Boiling for 45 min resulted in a large accumulation of DMA and a lesser increase in free FA in squid, but only negligible changes in cod. The decomposition of TMAO could not have been caused by enzymatic reactions. In a series of experiments with squid of different lots no consistent correlations were found between the shear force required to cut the cooked squid mantle and the contents of free FA. The rate of increase in free FA in the heated samples of the water-soluble fraction of squid flesh did not correspond to that of DMA.

Chemical and Functional Properties of Food Lipids provides a concise, straightforward treatment of the present state of knowledge of the nomenclature, content, composition, occurrence, distribution, chemical and biological reactivity, functional properties, and biological role of lipids in food systems. Written by a team of international researchers and based on the available world literature, this book examines the nature, technological properties, reactivity, and health-related concerns and benefits of food lipids. It covers the effects of storage and processing conditions on all aspects of quality of lipid-containing foods and reviews the current state of techniques for lipid analysis. The volume also discusses the importance of lipids in the human diet and includes a comparison of dietary recommendations for lipid intake. This is a valuable reference for researchers and graduate students in food chemistry and nutrition.

Hot smoked fish should fulfill the requirements set up for ready-to-eat foods. The total bacterial count on the raw material is 10(3) to 10(5) CFU per cm2 of skin and 10(2) to 10(9) CFU per gram of intestines. Contamination with pathogenic bacteria is very low, mainly with Clostridium botulinum, Listeria monocytogenes, Staphylococcus aureus, and Vibrio parahaemolyticus. In the premises of low hygiene, the contamination may increase due to unsanitary procedures, rotation of assigned duties of workers, and airborne microorganisms during packing of the product. Hot smoking in mild conditions at temperature in the fish not exceeding 65 degrees C and low concentration of salt does not inactivate all pathogens or inhibit bacteria during storage. Thus the required safety can be obtained only by using very fresh fish handled in hygienic conditions, controlling the processing and the plant hygiene in critical control points, and chilling of the product to about 2 degrees C. Most critical are the hygienic conditions in handling of the product after smoking. The use of preservatives for extending the shelf life of smoked fish is being investigated. High-quality shelf life of mild hot smoked mackerel at about 2 degrees C is at least 3 weeks.

Many nitrogenous compounds are involved in postmortem reactions in the muscles of animals, primarily as enzymes catalyzing the catabolysis of different tissue components. Thus, they contribute to changes in color, flavor, and rheological properties of the products. Furthermore, proteins and NPN participate also as substrates in reactions leading to the formation of products affecting the pH in the fish tissues. On the other hand, the rate and extent of changes in proteins are influenced by the products of degradation of saccharides and organic phosphates, as well as by the concentration of free ions, whereas these depend on the antemortem condition of the fish and on the temperature in the tissues after catch. A positive relationship of the enthalpy of activation of fish myofibrillar ATPase and the habitat temperature was demonstrated, from large negative values for cold-adapted species to high positive values for tropical species (Johnstone and Goldspink, 1975).

Heating, as applied in seafood technology, affects the rate of enzymatic processes, brings about denaturation and subsequent interactions of proteins, and accelerates chemical reactions of different tissue components. Therefore, heated seafoods change in color and in rheological properties, lose part of their water-retention capacity, and develop new, mostly very desirable flavor characteristics. The character and extent of these changes are affected by the rate, duration, and temperature of heating, as well as by the composition, biochemical state, and integrity of the food structure, the pH of the environment, the presence of different added substances, mainly salts, macromolecular extenders, and polyols, and the access of air (Aitken and Connell, 1979; Pan, 1990). Investigations on the effect of these factors should provide the fish processor with knowledge necessary to control the quality of cooked seafood products. Proper choice of heating rate, duration, temperature, and humidity may prevent losses in hot smoking of fish (Sikorski et al., 1984). Applying high enough time/temperature in cooking of crab may minimize leaching losses of soluble proteins and discoloration as well as facilitates the picking of the meat (Zaitsev et al., 1969; Dowdie and Biede, 1983).

Frozen fish stored several months at about −20°C may, after cooking, become tough, chewy, rubbery, stringy, or fibrous. This is accompanied by a loss in functional characteristics of the muscle proteins, mainly solubility, water retention, gelling ability, and lipid emulsifying properties. Freezing and thawing may result in lysis of mitochondria and lysosomes and a change in distribution of enzymes (Karvinen et al., 1982). A gradual decline in the activities of various muscle enzymes has also been observed during storage at freezing temperatures. The loss of ATPase activity, both in meat homogenates and in protein solutions, may reach 50–80% (Buttkus, 1967). The total solubility of proteins in neutral 5% NaC1 solution may decrease to about 30%, whereby the main loss regards the contractile proteins, mainly myosin heavy chain, M-proteins, tropomyosin, and troponins I and C in descending order (Owusu-Ansah and Hultin, 1992). It was shown by Jarenback and Liljemark (1975b), that the myosin microfibrils in fresh cod muscle could be almost totally extracted, whereas myosin in frozen muscle after prolonged storage was resistant to extraction. Significant changes in the sodium dodecyl sulfate—polyacrylamide gel electrophoresis (SDS—PAGE) and HPLC profiles of cod sarcoplasmic proteins due to frozen storage have been shown recently by LeBlanc and LeBlanc (1992b).

Collagen was isolated from the skin, connective tissue sheets, and mantle muscle of squid Illex argentinus and Loligo patagonica, by extracting all soluble noncollagenous material. The tissues and the collagen isolates were characterized by determining the total nitrogen, hydroxyproline, and solubility. The contents of hydroxyproline in the collagen isolate of skin, membranes, and muscle of Illex were 5.3, 8.0, and 4.4% dry matter and of Loligo 6.1, 7.4, and 4.9%, respectively. The collagen contents in these tissues were in Illex 4.9, 7.8, and 1.0; in Loligo 3.4, 4.9, and 0.3%, respectively, in the wet material. Collagen preparations obtained from the skin, membranes, and mantle muscle of Loligo yielded, respectively, 9%, 4%, and 8% collagen soluble in citrate buffer. For Illex squid the solubilities were 41%, 6%, and 21%, respectively.

Boiling frozen stored squid in 2% NaCl solution caused 30% weight loss after 5 min but changes in protein solubility and softening of the meat continued for at least 45 min. The influence of variability within the species on the texture of the cooked product was more significant than that of frozen storage. In discolored squid significant proteolysis was shown by electrophoresis. Such meat was less tough than that from nondiscolored specimens. Acetic acid cure induced proteolysis without improving texture, while polyphosphates softened the product without detectable proteolysis. The decisive effect on texture was displayed by pH and polyphosphates. Heating at 80° and 90°C left an uncooked sensory note.

Storage of frozen fish brings about a decrease of extractability of myofibrillar proteins. There is also deterioration of the texture and functional properties of the flesh. In model systems, aggregation of myosin, actin, tropomyosin, and whole myofibrils have been described. These changes are caused by concurrent action of partial dehydration due to the freezing out of water, exposure of the proteins to inorganic salts which are concentrated in the remaining nonfrozen fluid, interactions with free fatty acids liberated from phospholipids and with lipid oxidation products, and cross-linking by formaldehyde produced in some species of fish as a result of enzymic decomposition of trimethylamine oxide. The extent of protein alterations increases with time and temperature of storage as well as with advanced disintegration of the tissues and intermixing of their components. The role played by the individual factors and the significance of different types of bonds, i.e., hydrophobic adherences, ionic bonds, and covalent cross-links in particular cases are not yet fully disclosed. Retardation of the deteriorative changes of proteins in frozen fish is possible by avoiding high storage temperatures and oxidation of lipids, removing hematin compounds and other constituents promoting cross-linking reactions, and by adding cryoprotectors like sugars, several organic acids, amino acids, or peptides.

Many European and American fisheries have recently started to exploit oceanic and inshore squid resources. There is thus a need for developing domestic markets for squid products. The yield of edible parts of squid is 60–80% of the total weight and the chemical composition of the meat is similar to that of lean fish. However, the structure of the muscles is different, being composed of several layers of fibres running transversally to each other and covered with several sheets of connective tissue. A characteristic feature of squid proteins is a high proteinase activity and high solubility of the myofibrillar proteins during exhaustive extraction with water. The cooking loss in squid is up to about 40%. The texture, which does not resemble that of cooked fish, and the juiciness of the squid mantle, can be controlled by the cooking time and by pretreatment in polyphosphate solutions.

Krill, a small shrimp-like crustacean, is actually being exploited commercially in the Antarctic waters. In order to evaluate the offals generated during the processing of krill to food and feed products, as commercial sources of chitin, three kinds of shell waste were analysed. Depending upon the method of krill processing applied the shell waste contained 49–60% of proteinaceous material. The content of crude chitin in the dried deproteinised shells ranged from 34 to 49%. About 60% of the salt mixture impregnating the shells was phosphates and carbonates of calcium and magnesium.