!Fishery Products Quality, Safety and Authenticity 2009 (1).pdf

 FISHERY PRODUCTS Quality, safety and authenticity Edited by Hartmut Rehbein Jörg Oehlenschläger A John Wiley & Sons, Ltd., Publication FISHERY PRODUCTS  FISHERY PRODUCTS Quality, safety and authenticity Edited by...

 FISHERY PRODUCTS Quality, safety and authenticity Edited by Hartmut Rehbein Jörg Oehlenschläger A John Wiley & Sons, Ltd., Publication FISHERY PRODUCTS  FISHERY PRODUCTS Quality, safety and authenticity Edited by Hartmut Rehbein Jörg Oehlenschläger A John Wiley & Sons, Ltd., Publication This edition first published 2009 © 2009 Blackwell Publishing Ltd Blackwell Publishing was acquired by John Wiley & Sons in February 2007. Blackwell’s publishing programme has been merged with Wiley’s global Scientific, Technical, and Medical business to form Wiley-Blackwell. 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ISBN 978-1-4051-4162-8 (hardback: alk. paper) 1. Fishery products–Quality control. 2. Fishery processing–Quality control. I. Rehbein, Hartmut. II. Oehlenschläger, Jörg. SH335.5.Q35F58 2009 664′.94–dc22 2008039852 A catalogue record for this book is available from the British Library. Set in 10 on 12 pt Times by SNP Best-set Typesetter Ltd., Hong Kong Printed in Singapore 1 2009 Contents List of contributors xi Preface xiii Introduction xv Chapter 1 Basic facts and figures 1 Jörg Oehlenschläger and Hartmut Rehbein 1.1 Introduction 1 1.2 World fishery production 1 1.3 Categories of fish species 3 1.4 Fish muscle 4 1.5 Nutritional composition 4 1.6 Vitamins 10 1.7 Minerals 15 1.8 Post mortem changes in fish muscle 15 1.9 References and further reading 17 Chapter 2 Traditional methods 19 Peter Howgate 2.1 Introduction 19 2.2 TVB-N 20 2.3 Methylamines 23 2.4 Volatile acids 29 2.5 Volatile reducing substances 30 2.6 Indole 31 2.7 Proteolysis and amino acids 32 2.8 pH 33 2.9 Refractive index of eye fluids 33 2.10 Discussion and summary 34 2.11 References 35 Chapter 3 Biogenic amines 42 Rogério Mendes 3.1 Introduction 42 3.2 Factors affecting amine decarboxylase activity 44 3.3 Safety aspects 47 3.4 Quality assessment 49 v vi Contents 3.5 Regulatory issues 54 3.6 Methods of biogenic amine quantification 55 3.7 References 59 Chapter 4 ATP-derived products and K-value determination 68 Margarita Tejada 4.1 In vivo role of nucleotides 68 4.2 Post mortem changes 69 4.3 Methodology for evaluating the K-value or related compounds 79 4.4 Conclusions 81 4.5 References 81 Chapter 5 VIS/NIR spectroscopy 89 Heidi Anita Nilsen and Karsten Heia 5.1 Introduction 89 5.2 Analytical principles and measurements 89 5.3 Constituents: assessment of chemical composition 92 5.4 Freshness and storage time 96 5.5 Authentication 98 5.6 Safety 98 5.7 Other quality parameters 99 5.8 Summary and future perspectives 100 5.9 References 101 Chapter 6 Electronic nose and electronic tongue 105 Corrado Di Natale and Gudrun Ólafsdóttir 6.1 Introduction to the electronic nose and olfaction 105 6.2 Application of the electronic nose and electronic tongue 106 6.3 Colorimetric techniques, optical equipment and consumer electronics 108 6.4 Classification of fish odours 109 6.5 Quality indicators in fish during chilled storage: gas chromatography analysis of volatile compounds 111 6.6 Application of the electronic nose for evaluation of fish freshness 114 6.7 Combined electronic noses for estimating fish freshness 116 6.8 Conclusions and future outlook 119 6.9 References 120 Chapter 7 Colour measurement 127 Reinhard Schubring 7.1 Introduction 127 7.2 Instrumentation 128 7.3 Novel methods of colour evaluation 130  Contents vii 7.4 Colour measurement on fish and fishery products 131 7.5 Summary 159 7.6 References 159 Chapter 8 Differential scanning calorimetry 173 Reinhard Schubring 8.1 Introduction 173 8.2 Principle of function of the instruments 174 8.3 First applications of DSC on fish muscle and other seafood 178 8.4 Recent applications of DSC for investigating quality and safety 181 8.5 Summary 204 8.6 References 204 Chapter 9 Instrumental texture measurement 214 Mercedes Careche and Marta Barroso 9.1 Introduction 214 9.2 Instrumental texture 216 9.3 Texture measurement for quality classification or prediction 229 9.4 Conclusions 231 9.5 References 231 Chapter 10 Image processing 240 Michael Kroeger 10.1 Introduction 240 10.2 Quality characteristics from images 241 10.3 Spectral signature of images 243 10.4 Elastic properties from images 244 10.5 Analysis of image data 244 10.6 Results and discussion 245 10.7 Freshness determination from images 246 10.8 Firmness information from images 246 10.9 Conclusions 249 10.10 References 249 Chapter 11 Nuclear magnetic resonance 252 Marit Aursand, Emil Veliyulin, Inger B. Standal, Eva Falch, Ida G. Aursand and Ulf Erikson 11.1 Introduction 252 11.2 Magnetic resonance imaging 253 11.3 Low-field NMR 257 11.4 High-resolution NMR 259 11.5 The future of NMR in seafood 265 11.6 References 266 viii Contents Chapter 12 Time domain spectroscopy 273 Michael Kent and Frank Daschner 12.1 Introduction 273 12.2 Measurement system 275 12.3 Time domain reflectometry measurements 278 12.4 Conclusions 283 12.5 References 285 Chapter 13 Measuring electrical properties 286 Michael Kent and Jörg Oehlenschläger 13.1 Introduction 286 13.2 Fischtester 286 13.3 Torrymeter 287 13.4 Use of the Fischtester 294 13.5 Summary 296 13.6 References 297 Chapter 14 Two-dimensional gel electrophoresis 301 Flemming Jessen 14.1 Introduction 301 14.2 Two-dimensional gel electrophoresis (2DE) 302 14.3 2DE applications in seafood science 305 14.4 2DE-based seafood science in the future 310 14.5 References 312 Chapter 15 Microbiological methods 318 Ulrike Lyhs 15.1 Microorganisms in fish and fish products 318 15.2 General aspects of microbiological methods 320 15.3 Most probable number method 336 15.4 Molecular methods 336 15.5 References 338 Chapter 16 Protein-based methods 349 Hartmut Rehbein 16.1 Introduction 349 16.2 Fish muscle proteins 349 16.3 Electrophoretic methods for fish species identification 351 16.4 High-performance liquid chromatography 356 16.5 Immunological methods and detection of allergenic proteins 357 16.6 Determination of heating temperature 357 16.7 Differentiation of fresh and frozen/thawed fish fillets 359 16.8 References 359  Contents ix Chapter 17 DNA-based methods 363 Hartmut Rehbein 17.1 Introduction 363 17.2 DNA in fishery products 364 17.3 Genes used for species identification 366 17.4 Methods 368 17.5 Conclusions and outlook 379 17.6 References 380 Chapter 18 Other principles: analysis of lipids, stable isotopes and trace elements 388 Iciar Martinez 18.1 Introduction 388 18.2 Species and breeding stock identification by lipid analysis 389 18.3 Verification of the production method 394 18.4 Identification of the geographic origin 398 18.5 Future prospects 403 18.6 References 404 Chapter 19 Sensory evaluation of seafood: general principles and guidelines 411 Emilia Martinsdóttir, Rian Schelvis, Grethe Hyldig and Kolbrun Sveinsdóttir 19.1 General principles for sensory analysis 411 19.2 Application of sensory evaluation to fish and other seafood 417 19.3 References 422 Chapter 20 Sensory evaluation of seafood: methods 425 Emilia Martinsdóttir, Rian Schelvis, Grethe Hyldig and Kolbrun Sveinsdóttir 20.1 Introduction 425 20.2 Difference tests 425 20.3 Grading schemes 427 20.4 Quality index method 430 20.5 Descriptive sensory analysis 438 20.6 Consumer tests (hedonic) 440 20.7 References 440 Chapter 21 Data handling by multivariate data analysis 444 Bo M. Jørgensen 21.1 Introduction 444 21.2 What is multivariate data analysis? 444 21.3 Arrangement of data for bi-linear modelling 446 21.4 The outcome of bi-linear modelling 447 x Contents 21.5 Validation and prediction 451 21.6 Real examples and further reading 453 21.7 References 453 Chapter 22 Traceability as a tool 458 Erling P. Larsen and Begoña Pérez Villarreal 22.1 Introduction 458 22.2 Traceability from older times to the present 460 22.3 Traceability research in the seafood sector and other EU-funded food traceability projects 465 22.4 Validation of traceability data 466 22.5 Traceability in a global perspective 468 22.6 References 470 Index 472 List of Contributors Ida G. Aursand, SINTEF Fisheries and Aquaculture, N-7465 Trondheim, Norway; and Department of Biotechnology, NTNU, N-7491, Trondheim, Norway Marit Aursand, SINTEF Fisheries and Aquaculture, N-7465 Trondheim, Norway Marta Barroso, Instituto del Frío CSIC, c/José Antonio Novais 10, 28040 Madrid, Spain Mercedes Careche, Instituto del Frío CSIC, c/José Antonio Novais 10, 28040 Madrid, Spain Frank Daschner, Technische Fakultät der Christian-Albrecht-Universität, Institut für Elek- trotechnik und Informationstechnik, Kaiserstrasse 2, D-24143 Kiel, Germany Corrado Di Natale, Department of Electronic Engineering, University of Rome ‘Tor Vergata’, Via del Politecnico 1; 00 133 Roma, Italy Ulf Erikson, SINTEF Fisheries and Aquaculture, N-7465 Trondheim, Norway Eva Falch, SINTEF Fisheries and Aquaculture, N-7465 Trondheim, Norway Karsten Heia, Nofima, Marine, N-9291 Tromsø, Norway Peter Howgate, 26 Lavender Row, Stedham, Midhurst, West Sussex GU29 0NS, UK Grethe Hyldig, DTU Aqua, National Institute of Aquatic Resources, Technical University of Denmark, Søltofts Plads, Bygning 221, DK-2800 Kongens Lyngby, Denmark Flemming Jessen, DTU Aqua, National Institute of Aquatic Resources, Technical University of Denmark, Søltofts Plads, Building 221, DK-2800 Kongens Lyngby, Denmark Bo M. Jørgensen, DTU Aqua, National Institute of Aquatic Resources, Technical University of Denmark, Søltofts Plads, Building 221, DK-2800 Kongens Lyngby, Denmark Michael Kent, The White House, Greystone, Carmyllie, by Arbroath, Angus DD11 2RJ, UK Michael Kroeger, technet GmbH, Pestalozzistrasse 8, D-70563 Stuttgart, Germany Erling P. Larsen, DTU Aqua, National Institute of Aquatic Resources, Technical University of Denmark, Søltofts Plads, DTU, Bygning 221, DK-2800 Kongens Lyngby, Denmark Ulrike Lyhs, Ruralia-Institute, Seinäjoki Unit, University of Helsinki, Kampusranta 9C, 60320 Seinäjoki, Finland Iciar Martinez, SINTEF Fisheries and Aquaculture Ltd, 7465 Trondheim, Norway xi xii List of Contributors Emilia Martinsdóttir, Matís (Food research, Innovation and safety), Skulagata 4, IS-101 Reykjavík, Iceland Rogério Mendes, Department of Technological Innovation and Upgrading of Fishery Prod- ucts, INRB/IPIMAR, Av. De Brasilia, 1449-006 Lisboa, Portugal Heidi Anita Nilsen, NOFIMA, Marine, N-9291 Tromsø, Norway Jörg Oehlenschläger, Max Rubner Institute, Federal Research Institute for Nutrition and Food, Unit for Seafood Quality, Palmaille 9, D-22767 Hamburg, Germany Gudrun Ólafsdóttir, Department of Food Science and Nutrition, Faculty of Science, Uni- versity of Iceland, Hjardarhagi 2-6, 107 Reykjavík, Iceland; and Syni Laboratory Service, Lyngháls 3, 110 Reykjavík, Iceland Begoña Pérez Villarreal, Food Research Division, Txatxarramendi Ugartea z/g, 48395 Sukarrieta (Bizkaia), Spain Hartmut Rehbein, Max Rubner Institute, Federal Research Institute for Nutrition and Food, Unit for Seafood Quality, Palmaille 9, D-22767 Hamburg, Germany Rian Schelvis, Wageningen IMARES, P.O. Box 68, NL-1970 AB IJmuiden, The Netherlands Reinhard Schubring, Max Rubner Institute, Federal Research Institute for Nutrition and Food, Unit for Seafood Quality, Palmaille 9, D-22767 Hamburg, Germany Inger B. Standal, SINTEF Fisheries and Aquaculture, N-7465 Trondheim, Norway; and Department of Biotechnology, NTNU, N-7491, Trondheim, Norway Kolbrun Sveinsdóttir, Matís (Food research, Innovation and safety), Skulagata 4, IS-101 Reykjavík, Iceland Margarita Tejada, Instituto del Frío (CSIC), José Antonio Novais, 10, 28040 Madrid, Spain Emil Veliyulin, SINTEF Fisheries and Aquaculture, N-7465 Trondheim, Norway Preface The contribution of fisheries and aquaculture to the human food supply has increased very significantly in recent decades. What is remarkable for this part of the food sector is the large share of fish that enters international trade, with some 37% of all fish caught and cul- tured being traded across national borders. So it can be argued that fish and fishery products are in the forefront of globalization, as products from all corners of the world can be found on the international market. There are many interesting facets to how this came about, in particular how well developing countries have adapted to the strict trading regimes of the modern marketplace for fish and fishery products. As food retailers consolidate in ever-larger units, the competition for customers intensifies. This has direct effects through the whole supply chain, not least primary producers. Besides, large retailers now have so much reputation at stake that they spend large sums of money to minimize the risk of ‘food scandals’ ever being attributable to the products they sell. This translates into ever more and stricter food safety and quality criteria with which all the actors in the food chain have to comply. This is one of the reasons for a rise in private standards of various sorts that are stricter than the standards set by governments. This rise in private standards is seen by many as a potential new form of protectionism. The objective of the World Trade Organization (WTO) is to facilitate free trade between nations to ‘improve the welfare of the peoples of the Member Countries’. The WTO Agreements, particularly the Sanitary and Phytosanitary Agreement (SPS) and the Technical Barriers to Trade Agree- ment (TBT), were set as the framework within which technical standards would be operated. In 1995 it was decided that the food standards of the Codex Alimentarius would be the standards used to resolve safety and quality questions in international trade disputes. Free trade is a very important issue on the international agenda. The international system created through the WTO is meant to create a ‘level playing field’ so that all can participate in international trade and to allow ‘trade to flow smoothly, freely, fairly and predictably.’ Thus, the importance of food standards to ascertain if they comply with agreed minimum criteria. The SPS Agreement stipulates that food standards should be based on sound science and be risk based. There is also a call for harmonization of standards and equivalence of different national standards relating to food safety management systems as long as they adhere to the same level of protection. That is a brief description of the framework, but all food standards are linked to specific methods by which compliance with them is measured. This book deals with the methods commonly used to measure the quality of fish and fishery products. Going through it is truly a story attesting to the great progress that has been made in this area in recent decades. It is interesting to see how the science has moved forward to increasing automation and online, non-destructive methods to ascertain characteristics of the products. It is also interesting to see how sensory evaluation, which not so long ago was considered subjective and thus unscientific, has been turned into an objective scientific tool in its own right. Competition in the food market makes it imperative for retailers not only to present prod- ucts that are safe to eat and taste good, but also nutritionally balanced. Increasingly they xiii xiv Preface also have to comply with environmental criteria such as not originating from a fish stock that is overfished or from vessels fishing illegally. In such a competitive environment, it is tempting for producers to cut corners. Water can be added to increase weight, expensive fish species can be substituted by cheaper ones or chemicals can be added to remove smells, to name only a few examples. At the same time, any wrongdoing or fraud can inflict huge damage in lost reputation for the producing countries and retailers. Therefore, objective analytical methods to verify and check compliance are of the utmost importance at all levels in today’s food chains. I therefore congratulate the authors for this important contribution to a seafood sector that aspires to deliver safe, tasty and wholesome food to the demanding modern consumer. The seafood sector has been in the forefront of globalization and this book will contribute to ensuring that quality and safety standards will be implemented by processors both in developed and developing countries. Grimur Valdimarsson Director Fish Products and Industry Division Fisheries and Aquaculture Department Food and Agriculture Organization of the United Nations Rome Italy Introduction When we started our careers as analytical chemists and biochemists in a seafood-dedicated institution more than 30 years ago, there were only a few analytical methods known to analyse safety and quality of seafood and which were used as well in research as in industry. The important methods were few: electrical devices as the Fischtester and Torrymeter; total volatile basic nitrogen (TVBN) for the determination of spoilage (often wrongly referred to as a freshness determination method); colony-forming units (cfu) in microbiology; and some methods for the determination of proximate composition, additives and non-desirable com- ponents. Textbooks, especially about analytical methods applied in seafood research and seafood-related industry, were missing; and monographs in this field were rare. Worthy of mention are the books written by Ludorff and Meyer (1973, in German), Connell (1995, 4th edition) and Botta (1995). More recently (2003), a book was edited by Luten, Oehlenschläger and Olafsdottir containing some chapters with information about instrumental and sensory measurement techniques. During the past 30 years the situation has changed dramatically. The changes were mainly initiated by two major causes. Firstly, there was a rapid development in the field of analytical instrumental methods, both in further development or application of existing and novel methods. Secondly, development in the research framework programmes of the European Commission enabled scientists not only to travel to congresses to meet and talk to their peers but also to conduct integrated research projects together. The latter has been very effective in the past 15–20 years. The results of these research projects and Concerted Actions led to a jump forward in seafood-related instrumental techniques in Europe. We ourselves have participated in several research projects, of which a few that were very productive and future-orientated are worth mentioning. The Concerted Actions ‘Evaluation of fish freshness’ and ‘Fish quality labelling and monitoring’, and the Research Projects ‘Multi-sensor techniques for monitoring the quality of fish (MUSTEC)’, ‘Seafood quality identification (SEQUID)’, and ‘Identification of species in processed seafood products using DNA-based diagnostic techniques’. Many of the authors in this book have also been partners in such research projects and have been selected to be contributors based on their skills and experience provided there. Unfortunately, many results obtained in the research projects have been hidden in confidential reports and never published. One of us (J.O.) has been chairman of the ‘WEFTA (Western European Fish Technologists’ Association) Working Group on Analytical Methods in Fish and Fishery Products’ since 1988. During this time,we increasingly desired to collect and publish the knowledge about modern analytical methods from all the different disciplines in a comprehensive book to make it available in a convenient form for the reader. From the first idea to realisation took many years, but the results are now in your hands. To our knowledge, this is the first book that concentrates on instrumental methods used in the seafood world. It is not a textbook about analytical methods but a guidebook for applied methodologies in the seafood area. It was our aim to present chapters that could be used by a wide range of interested readers, from students or beginners in the field who want xv xvi Introduction to get a first overlook about the topic and who can be guided further by the numerous refer- ences, to advanced readers who will certainly find some new information that cannot be obtained elsewhere in such a concentrated and condensed form. The book contains chapters about traditional, instrumental, microbiological, sensory and authenticity methods. Finally, it has two chapters about multivariate data analysis and traceability. The book does not include chapters about determination of organic and inorganic pollut- ants for two reasons: (1) there are excellent books already available on analytical chemistry; (2) the importance of the topic and the multitude of analytical methods and pollutants would need a separate book. The chapters have been written by scientists who are all intensively working in their respective areas and who are highly specialised. Nevertheless, it is our hope that the chapters and the whole book are easily readable and understandable. We are very grateful to all authors who have contributed to this book; we thank them deeply for their patience and willingness to consider our wishes for changes, amendments and additions to the chapters during the preparation of the book. We especially thank Dr Ute Ostermeyer (Max Rubner-Institute, Hamburg, Germany), who has considerably contributed to the section about vitamins in the introductory chapter. We further thank the anonymous reviewers who have read the chapters and given valuable advice. May this book be a reference for seafood-related analytical techniques for years to come! Hartmut Rehbein Jörg Oehlenschläger Chapter 1 Basic facts and figures Jörg Oehlenschläger and Hartmut Rehbein 1.1 Introduction With more than 30,000 known species, fish form the biggest group in the animal kingdom that is used for the production of animal-based foods. Only about 700 of these species are commercially fished and used for food production. Further, some 100 crustacean and 100 molluscan species (for example mussels, snails and cephalopods) are used as food for humans. The amount captured worldwide is registered annually by the Food and Agriculture Organization of the United Nations (FAO). Fish and other seafood are very important in covering a part of the protein demand for humans. In 2000, food fish contributed 15.9% to the human diet on a worldwide basis (fish as a percentage of total animal protein intake). There are, however, great differences between continents and countries. In low-income, food-deficient countries (LIFDC) fish contributes 20.6%, in Asia 23.3%, in China 21.1%, whereas in South America the contribu- tion amounts only to 5.7%, in North and Central America to 7.1% and in Europe to 10.3%. The average contribution in developed countries is 12% whereas it is 18.8% in developing countries (FAO). 1.2 World fishery production World fishery production has been developing rapidly since 1950 (Table 1.1). In 1948 only 22 million metric tonnes of fish were captured, whereas in 2004 the world production amounted to more than 140 million tonnes. The dramatic increase of captured fish from 1950 to 1975 was followed by a somewhat more moderate increase between 1975 and 1990, and stagnation since then. Today, most fish stocks are fully exploited and a few are even overexploited. The growth in world fishery production in the past 10–15 years is based on a steadily growing aquaculture. The proportion of species farmed by aquaculture of the total world fishery production amounts today to more than 40%. The countries contributing most to total world fishery production of 140,457 million tonnes in 2004 are listed in Table 1.2. In Table 1.3 the major captured fish species are listed, and in Table 1.4 the major species farmed by aquaculture. Of this world fishery production of 140,457 million tonnes, 105,632 million tonnes (75.2%) were used for human consumption. Of these 75%, 39% were marketed fresh, 19% frozen, 8% cured and 9% canned. 1 2 Fishery Products: Quality, safety and authenticity Table 1.1 Development of world fish production (catch and aquaculture) since 1900. Year 1900 1948 1958 1968 1978 1988 1995 1998 2004 Million tonnes 4 22 40 67 73 99 117 118 140 Table 1.2 World fishery production: top 10 countries in 2004. Country Capture Aquaculture Total (tonnes) China 16,892,793 30,614,968 47,507,761 Peru 9,613,180 22,199 9,635,379 India 3,615,724 2,472,335 6,088,059 Indonesia 4,811,320 1,045,051 5,856,371 Chile 4,935,376 674,979 5,610,355 USA 4,959,826 606,549 5,566,375 Japan 4,401,341 776,421 5,177,762 Thailand 2,845,088 1,172,866 4,017,954 Norway 2,522,225 637,993 3,160,218 Vietnam 1,879,488 1,198,617 3,078,105 Table 1.3 World fishery production in 2004: fish species captured (greater than 1 million metric tons). Species Taxonomic name Amount captured (tonnes) Peruvian anchovy Engraulis ringens 10,679,338 Alaska pollock Theragra chalcogramma 2,691,939 Blue whiting Micromesistius poutassou 2,427,862 Skipjack tuna Katsuwonus pelamis 2,092,356 Atlantic herring Clupea harengus 2,019,933 Chub mackerel Scomber japonicus 2,017,276 Japanese anchovy Engraulis japonicus 1,795,844 Chilean jack mackerel Trachurus murphyi 1,778,777 Largehead hairtail Trichiurus lepturus 1,587,452 Yellowfin tuna Thunnus albacares 1,384,358 European pilchard Sardina pilchardus 1,062,432 Table 1.4 World aquaculture production of fish, crustaceans and molluscs in 2004 (greater than 1 million metric tonnes). Species Taxonomic name Quantity (tonnes) Pacific oyster Crassostrea gigas 4,429,337 Silver carp Hypophthalmichthys molitrix 3,979,292 Grass carp Ctenopharyngodon idellus 3,876,868 Carp Cyprinus carpio 3,387,918 Japanese carpet shell Ruditapes philippinarum 2,860,152 Bighead carp Hypophthalmichthys nobilis 2,101,688 Crucian carp Carassius carassius 1,949,758 Nile tilapia Oreochromis niloticus 1,495,744 Whiteleg shrimp Penaeus vannamei 1,386,382 Atlantic salmon Salmo salar 1,244,637 Japanese scallop Patinopecten yessoensis 1,126,159  Basic facts and figures 3 Part of the world fishery catch is processed into fish meal, which is used as a fertiliser or as animal (mainly fish) feed. For this, some target fish species such as sand eel and anchoveta (so-called ‘industry fish’) are caught. The fish oil recovered during the fish meal process is to some extent also used for human nutrition. The stagnation of the world fish catch has led to an intensive discussion about better use and management of the resources. Also, quality aspects that have been neglected for many years are back on the agenda (careful handling of the the catch, prolonged shelf life of ice- and frozen-stored fish, optimisation of yield in fish processing machines, etc.). 1.3 Categories of fish species Fish species can be divided into categories, for example according to their habitat as marine and freshwater species. Some species such as European eel and most salmon can live in both Table 1.5 Categories of marine and freshwater fish species according to their total fat content in edible tissue (fillet). Total fat Category content (%) Common names Taxonomic names Lean fish 1–5 White halibut, wolffish, Hippoglossus hippoglossus, low fat plaice, hake, dab, grey Anarhichas lupus, Anarhichas content mullet, red mullet, minor, Pleuronectes platessa, redfish, whitch, sole, Merluccius merluccius, Limanda turbot, brill, trout, limanda, Mugil cephalus, Mullus tench, whitefish surmuletus, Sebastes marinus, Sebastes mentella, Glyptocephalus cynoglossus, Solea solea, Psetta maxima, Scophtalmus rhombus, Trutta trutta, Tinca tinca, Coregonus sp. Medium fatty >5–10 Redfish, sardine, Sebastes marinus, Sebastes fish species swordfish, Bream, mentella, Sardina pilchardus, catfish, albacore, Xiphias gladius, Abramis brama, dogfish, tuna, conger, Silurus glanis, Squalus acanthias, salmon Thunnus thynnus, Conger conger, Salmo salar Fatty fish >10 Sprat, black halibut, Sprattus sprattus, Hippoglossoides species mackerel, herring, eel platessoides, Scomber scombrus, Clupea harengus, Anguilla anguilla 4 Fishery Products: Quality, safety and authenticity environments. Typical representatives of freshwater fish are: carp, pike, perch, pikeperch, tench; examples of marine fish are: cod, saithe, redfish, mackerel and herring. Often, their anatomical shape is also used for categorisation: roundfish such as saithe, cod and hake; flat fish species such as plaice, dab and flounder; and snake-shaped fish such as eel, lamprey and moray. Also, the categories groundfish and swarmfish are used. Groundfish are those species that search for their prey close to the bottom of the sea (cod, flat fish); swarm fish are those that gather in big schools, mainly the small, pelagic, fatty species such as herring, sprat and sardine. Most species belong to the group of bony fish (Osteichthyes), which means that they have a fully developed bony skeleton. Some fish species have so-called real bones which are not attached to the backbone or to other bones but are located free in the muscle tissue. These bones are formed by hardened connective tissue. Sharks, rays and chimaeras belong to the group of cartilagenous fish (Chondrichthyes). They have no bones, but a cartilaginous tissue which is enforced by calcium carbonate. Fish species can also be divided into four classes (Table 1.5) based on their nutritional properties, for example their fat content, which can vary in some species depending on their state of maturity from 1% to 30%. 1.4 Fish muscle Fish flesh, fish muscle or fish fillet is the name for the body musculature of fish reaching from head to tail: this muscle forms the major part of the edible portion of fish. This side muscle consists of segments (myomers) lying between connective tissue layers (myocom- mata). The muscle fibres within the myomers are longitudinally orientated. The proportion of fish flesh to total body weight varies between 40% and 65%, depending of species, shape, age and the physiological status of the fish. Fish with more elliptical cross sections (tuna, herring and salmon) exhibit a much higher proportion of the edible part than flatfish species or species with very big heads such as monkfish. Fish flesh consists of light and dark musculature. Both types can be differentiated by chemical composition, physiological importance and nutritional value. Most species have more light than dark muscle. Herring and mackerel have approximately equal amounts of light and dark muscle. The dark muscle occurs just below the skin in the area of the lateral line, and continues as a wedge shape to the backbone. The light musculature is used for rapid, sudden movements and obtains energy mainly from anaerobic glycolysis. For continuous swimming, fish use their dark musculature. This type of muscle is therefore well developed in pelagic species (herring, mackerel, tuna), well supplied with blood and rich in myoglobin. The metabolism of dark muscle is aerobic; energy is provided by lipids and carbohydrates. 1.5 Nutritional composition The nutritional composition of fish (Tables 1.6 and 1.7) is comparable to that of warm- blooded animals; in relation to essential elements such as selenium and iodine, it is superior. Table 1.6 Compositional data of edible part (fillet) of marine and freshwater fish species. Data are average values calculated or estimated and rounded from several food composition tables as well as from our analyses and can be subject to great variations depending on intrinsic fish parameters such as state of maturity, sex, age, season, nutritional status, etc. Fish species Common Channel Anchovy Sea bass Bluefish Burbot carp catfish Cod Pacific cod Cusk Eel Engraulis Morone Pomatomus Lota Cyprinus Ictalurus Gadus Gadus Brosme Anguilla Components encrasicolus saxiatilis saltatrix lota carpio punctatus morhua macrocephalus brosme anguilla Moisture (g/100 g) 73 79 71 79 67 80 81 81 76 68 Raw protein (g/100 g) 20 18 20 19 18 16 18 18 19 18 Total lipids (g/100 g) 5 2 4 1 6 3 0.5 0.4 0.7 12 Ash (g/100 g) 1.4 1 1 1.2 1.5 1 1.2 1.2 1.3 1.4 Energy (kcal/100 g) 131 97 124 90 127 95 82 82 87 184 Energy (kJ/100 g) 548 406 519 377 531 397 343 343 364 770 Calcium (mg/100 g) 147 15 7 50 41 14 16 7 10 20 Magnesium (mg/100 g) 41 40 33 32 29 23 32 24 31 20 Phosphorus (mg/100 g) 174 198 227 200 415 209 203 174 204 216 Potassium (mg/100 g) 383 256 327 404 333 358 413 403 392 272 Sodium (mg/100 g) 104 69 60 97 49 43 54 71 31 51 Basic facts and figures Zinc (mg/100 g) 1.7 0.4 0.08 0.8 1.5 0.5 0.5 0.4 0.3 1.6 Copper (mg/100 g) 0.2 0.03 0.05 0.2 0.06 0.03 0.03 0.03 0.02 0.02 Manganese (mg/100 g) 0.07 0.12 0.2 0.7 0.04 0.03 0.02 0.01 0.02 0.04 Selenium (μg/100 g) 37 375 375 136 13 13 33 37 37 7 Iodine (μg/100 g) 187 20 : 5 (n − 3) (g/100 g) 0.538 0.169 0.252 0.07 0.238 0.13 0.064 0.08 Total 0.084 PUFA 22 : 6 (n − 3) (g/100 g) 0.911 0.585 0.519 0.096 0.114 0.234 0.12 0.135 0.28 0.063 Cholesterol (mg/100 g) 30 80 59 60 66 58 39 37 41 51 5  6 Fishery Products: Quality, safety and authenticity Table 1.6 Continued Fish species Greenland Haddock White halibut halibut Herring Ling Mackerel Monkfish Mullet Redfish Melanogrammus Hippoglossus Rheinhardtius Clupea Molva Scomber Lophius Mugil Sebastes Components aeglefinus hippoglossus hippoglossoides harengus molva scombrus piscatorius cephalus marinus Moisture (g/100 g) 78 78 70 72 80 64 83 77 79 Raw protein (g/100 g) 19 21 14 18 19 19 15 19 19 Total lipids (g/100 g) 0.7 2.3 14 9 0.6 14 1.5 3.8 1.6 Ash (g/100 g) 1.2 1.4 1 1.5 1.4 1.4 1.2 1.2 1.2 Energy (kcal/100 g) 87 110 186 158 87 205 76 117 94 Energy (kJ/100 g) 364 460 778 661 364 858 318 490 393 Calcium (mg/100 g) 33 47 3 57 34 12 8 41 107 Magnesium (mg/100 g) 39 83 26 32 63 76 21 29 30 Phosphorus (mg/100 g) 188 222 164 236 198 217 200 221 216 Potassium (mg/100 g) 311 450 268 327 379 314 400 357 273 Sodium (mg/100 g) 68 54 80 90 135 90 18 65 75 Zinc (mg/100 g) 0.3 0.4 0.4 1 0.3 0.6 0.3 0.5 0.5 Copper (mg/100 g) 0.06 0.03 0.03 0.09 0.1 0.07 0.03 0.05 0.03 Manganese (mg/100 g) 0.03 0.02 0.01 0.04 0.03 0.02 0.02 0.02 0.02 Selenium (μg/100 g) 30 37 37 36 36 44 36 36 43 Iodine (μg/100 g) 186 22 74 41 175 109 27 70 20 : 5 (n − 3) (g/100 g) 0.059 0.071 0.526 0.709 Total 0.898 Total 0.217 0.08 22 : 6 (n − 3) (g/100 g) 0.126 0.292 0.393 0.862 PUFA 1.401 PUFA 0.108 0.211 0.22 0.61 Cholesterol (mg/100 g) 36 45 42 31 31 33 33 49 42  Fish species Orange Bluefin Yellowfin Pike Saithe Alaska Pollack roughy tuna Skipjack tuna Turbot Wolffish Esox Pollachius Theragra Hoplostetus Thunnus Euthynnus Thunnus Psetta Anarhichas Components lucius virens chalcogramma atlanticus thynnus pelamis albacares maxima lupus Moisture (g/100 g) 79 78 82 76 68 71 71 77 80 Raw protein (g/100 g) 19 19 17 15 23 22 23 16 18 Total lipids (g/100 g) 0.7 1 0.8 0.7 5 1 15 3 2 Ash (g/100 g) 1.2 1.4 1.2 0.9 1.2 1.3 1.3 2 1.2 Energy (kcal/100 g) 88 92 81 69 144 103 168 95 96 Energy (kJ/100 g) 368 385 339 289 602 431 452 397 402 Calcium (mg/100 g) 57 60 5 30 8 29 16 18 6 Magnesium (mg/100 g) 31 67 57 30 50 34 50 51 30 Phosphorus (mg/100 g) 220 221 376 200 254 222 191 129 200 Potassium (mg/100 g) 259 356 326 300 252 407 444 238 300 Sodium (mg/100 g) 39 86 99 63 39 37 37 150 85 Zinc (mg/100 g) 0.67 0.37 0.44 0.75 0.6 0.82 0.52 0.22 0.78 Copper (mg/100 g) 0.05 0.05 0.04 0.1 0.09 0.09 0.06 0.04 0.03 Basic facts and figures Manganese (mg/100 g) 0.2 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 Selenium (μg/100 g) 12 36 22 36 36 36 36 36 36 Iodine (μg/100 g) 121 46 180 20 : 5 (n − 3) (g/100 g) 0.033 0.071 0.15 0.283 0.071 0.037 Total 0.307 PUFA 22 : 6 (n − 3) (g/100 g) 0.074 0.35 0.22 0.890 0.185 0.181 0.88 0.316 Cholesterol (mg/100 g) 39 31 71 20 38 47 45 39 43 Continued 7  8 Fishery Products: Quality, safety and authenticity Table 1.6 Continued Fish species Salmon Chinook Keta Coho Swordfish Components Salmo salar Oncorhynchus tschawytscha Oncorhynchus keta Oncorhynchus kisutch Xiphias gladius Moisture (g/100 g) 69 73 75 73 76 Raw protein (g/100 g) 20 20 20 22 20 Total lipids (g/100 g) 6 10 4 6 4 Ash (g/100 g) 2.5 1.4 1.2 1.2 1.5 Energy (kcal/100 g) 142 180 120 146 121 Energy (kJ/100 g) 594 753 502 611 506 Calcium (mg/100 g) 12 22 11 36 4 Magnesium (mg/100 g) 29 95 22 31 27 Phosphorus (mg/100 g) 200 289 283 262 263 Potassium (mg/100 g) 490 394 429 423 288 Sodium (mg/100 g) 44 47 50 46 90 Zinc (mg/100 g) 0.6 0.4 0.5 0.4 1.2 Copper (mg/100 g) 0.3 0.04 0.06 0.05 0.1 Manganese (mg/100 g) 0.02 0.02 0.02 0.01 0.02 Selenium (μg/100 g) 37 36 35 36 48 Iodine (μg/100 g) 45 20 : 5 (n − 3) (g/100 g) 0.32 0.788 0.233 0.429 0.108 22 : 6 (n − 3) (g/100 g) 1.12 0.567 0.394 0.656 0.531 Cholesterol (mg/100 g) 26 66 74 45 39 Table 1.7 Compositional data of edible part (fillet) of marine crustacean and molluscan shellfish species. Data are average values calculated or estimated and rounded from several food composition tables as well as from our analyses and can be subject to great variations depending on intrinsic fish parameters such as state of maturity, sex, age, season, nutritional status, etc. Crustacean and molluscan shellfish species Pacific American Common Blue American Dungeness oyster oyster octopus mussle lobster Snow crab crab Blue crab King crab Crassostrea Crassostrea Octopus Mytilus Homarus Chionoectes Cancer Callinectes Paralithodes Components gigas virginica vulgaris edulis americanus opilio magister sapidus camtschatica Moisture (g/100 g) 82 85 80 81 77 81 79 79 80 Raw protein (g/100 g) 9.5 7 15 12 19 19 17 18 18 Total lipids (g/100 g) 2 2 1 2 1 1 1 1 0.6 Ash (g/100 g) 1.2 1.4 1.6 1.6 2.2 2 1.7 1.8 1.8 Energy (kcal/100 g) 81 68 82 86 90 90 86 87 84 Energy (kJ/100 g) 339 285 343 360 377 377 360 364 351 Calcium (mg/100 g) 8 45 53 26 48 26 46 89 46 Iron (mg/100 g) 5 6.7 5.3 4 0.3 2.5 0.4 0.7 0.6 Magnesium (mg/100 g) 22 47 30 34 27 49 45 34 49 Phosphorus (mg/100 g) 162 135 186 197 144 133 182 229 219 Potassium (mg/100 g) 168 156 350 320 275 173 354 329 204 Sodium (mg/100 g) 106 211 230 286 296 539 295 293 836 Basic facts and figures Zinc (mg/100 g) 17 91 1.7 1.6 3 2.8 4.3 3.5 6 Copper (mg/100 g) 1.6 4.5 0.4 0.1 1.7 0.6 0.7 0.7 0.9 Manganese (mg/100 g) 0.6 0.4 0.03 3.4 0.06 0.03 0.08 0.2 0.04 Selenium (μg/100 g) 77 64 45 45 41 35 37 37 36 Iodine (μg/100 g) 25 99 20 : 5 (n − 3) (g/100 g) 0.438 0.268 0.076 0.188 Total 0.259 0.219 0.17 Total PUFA PUFA 22 : 6 (n − 3) (g/100 g) 0.25 0.292 0.081 0.253 0.15 0.113 0.088 0.15 0.13 Cholesterol (mg/100 g) 50 53 48 28 95 55 59 78 42 9 10 Fishery Products: Quality, safety and authenticity The protein of fish muscle is rich in essential amino acids, has a high biological value and can be digested easily. The amount of connective tissue is low (1–2%) compared with warm-blooded animals (10–13%). The content of non-protein nitrogen (NPN) components in fish flesh is high. The main components are creatine (200–700 mg/100 g), trimethylamine oxide (100–1000 mg/100 g), adenosine nucleotides (200–400 mg/100 g), free amino acids and dipeptides. Chondrich- thyes contain high amounts of urea. The average sum of NPN amounts to 420 mg/100 g and contributes to 15% of raw protein content (nitrogen content × 6.25). The fat content of fish varies greatly in quantity and fatty acid composition. The protein content is almost constant. The fat content is mainly dependent on biological state of maturity, but also on nutritional status, age, catching ground and season. The fat is not homogeneously distributed in the body. In lean fish species, it is located in the liver as an energy reservoir; in fatty species, it is deposited in the muscle tissue, as a subcutaneous layer under the skin or in the intestines. In many fatty fish species, a linear correlation exists between the fat and water content of muscle tissue. Lean fish species have a higher proportion of polar lipids (phosphatidylcholine and phos- phatidylethanolamine) than fatty fish species, in which the fat consists mainly of neutral lipids (triacylglycerols). The polar lipids are mainly located in the lipid bilayer of the cell membranes, whereas the neutral lipids are located in the fat cells of the energy reservoirs (liver, muscle). The cholesterol content of fish muscle is generally low (35 mg/100 g). Fish lipids differ from those of terrestrial animals mainly in their high content of long- chain, highly unsaturated fatty acids of the n–3 series (eicosapentaenoic acid, 20 : 5 and docosahexaenoic acid, 22 : 6), often referred to as polyunsaturated fatty acids (PUFAs). The content of these PUFAs in fatty fish species can be high: dogfish 3 g/100 g, herring 2.3 g/100 g, mackerel 4.6 g/100 g, salmon 2.3 g/100 g and tuna 2.1 g/100 g. The highly unsaturated character of these fatty acids is the reason why they are susceptible to lipid oxidation and oxidative degradation. Fatty fish species therefore have a tendency to exhibit rancid tastes and odours after limited storage time. 1.6 Vitamins The vitamin contents in fish are species specific. They can vary considerably within one species with age, size, sex, season, diet, state of health and geographic location. In fish farmed by aquaculture, the contents of vitamins reflect the composition of the corresponding components in the fish feed. Therefore, the vitamin content of wild and farmed fish can be different. From different food composition tables, the mean vitamin contents in raw muscle are summarised in Table 1.8a, b for several marine fish and in Table 1.9a, b for freshwater fish. 1.6.1 Fat-soluble vitamins The liver of fish is a rich source of fat-soluble vitamins (A, D, E and K). In fish flesh, dark muscle contains more fat-soluble vitamins than white muscle because of its higher fat content. Table 1.8a Fat-soluble vitamins in marine fish species (μg/100 g edible portion). Species Taxonomic name Fat (g/100 g) Vitamin A Vitamin D Vitamin E Vitamin K1 Anchovy Engraulis encrasicolus 2.3 19 20 500 Anglerfish Lophius piscatorius 0.1–1.5 8–80 1–2 500–1000 n.d. Atlantic halibut Hippoglossus hippoglossus 1.6–10.4 PO43− treatment. Myosin treated with Cl− and PO43− showed lower ΔH values on heating than the control, which is likely due to denaturation and unfolding of myosin by acid treatments. Among the two anions, PO43− treatment showed lower ΔH than Cl− treatment, indicative of greater denaturation of myosin by PO43− treatment (Raghavan and Kristinsson 2007). Richards et al. (2007) compared thermal stability of haemoglobin from tilapia (Oreochro- mis niloticus) with that from trout (Onchorhynchus mykiss) by microDSC. Tilapia haemo- globin had a single peak at 61 °C, whereas trout haemoglobin had one peak at 52 °C and another at 60 °C. Scans were conducted only at pH 7.4, as reliable results could not be obtained at pH 6.3 owing to extensive aggregation. 8.4.2 DSC measurements taken on invertebrates The Argentine group of Crupkin specialises in this field. During the past 10 years, numerous papers have been published dealing with DSC measurements on mussels (Aulacomya ater ater), squid (Illex argentinus) and scallop (Zygochlamys patagonica). Whole adductor muscle of mussel free of connective tissue showed two transitions (Tmax 50.5 and 72.5 °C) and ΔH of 2.5 cal/g. Sarcoplasmic proteins contributed to both denaturation peaks. The DSC curves of actomyosin were similar to those of whole muscle. Two endothermic peaks (36 and 50.5 °C) were observed in the DSC curve of myosin. DSC curves corresponding to 184 Fishery Products: Quality, safety and authenticity actomyosin, paramyosin and sarcoplasmic proteins indicated that myosin and paramyosin contribute mainly to the first transition and that actin is responsible for most of the second transition in whole muscle. Thermal stability of whole muscle decreased with increasing pH and ionic strength. Total denaturation enthalpy significantly decreased with an increase of the ionic strength (Paredi et al. 1994). Post mortem thermal behaviour of the striated adductor muscles of mussel stored at 2–4 °C was characterised as follows. The exothermal peak present in pre rigor muscles from other species, such as fish or mammalian muscles, was not evident in DSC curves of either fresh or cold-stored adductor muscles. In the first 8 h of storage, the greatest increases in both total ΔH and ΔH related to the first endothermal transition were observed. It was suggested that onset of rigor mortis in the mussel can be determined by enthalpy measurements (Paredi et al. 1995). Mussels (Perna canicula), which were thermally treated during process- ing to facilitate an easier removal of shells, were investigated on their degree of doneness by DSC. DSC curves of differently treated samples revealed by the number of peaks identified as well as by their ΔH that trade samples in question were only blanched and not completely well cooked (Rehbein and Schubring 1996). The DSC curves of whole muscle of female squid showed four endothermic transitions, with Tmax equal to 45.9, 56.8, 67.2 and 79.2 °C, respectively. DSC curves of whole muscle of male squid showed three transitions, with Tmax equal to 47.9, 56.8, and 79.2 °C, respec- tively. Tmax of 67.2 °C, present only in female squid muscle, was related to sarcoplasmic proteins. Myosin and paramyosin contributed to the first transition, connective tissues to the second transition, and actin to the last transition. No major differences were observed in Tmax values that were related to the sex and sexual maturation stage of specimens. The lowest ΔH was found in muscle from immature females. Independent of sex and sexual maturation stage of specimens, no major changes were observed in either Tmax or ΔH during frozen storage of squid (Paredi et al. 1996). DSC curves of both striated and smooth muscles free of connective tissue derived from scallop showed two transitions, Tmax of 53.2 and 79 °C, and Tmax of 52.7 and 78 °C, respectively. These results indicate that the different paramyosin content of the muscles did not influence the thermal stability of their proteins. DSC curves of myofibrils and actomyosin were similar to those corresponding to respective whole muscles. Myosin from striated muscles showed a cooperative single peak, with Tmax equal to 48.8 °C. Similar Tmax values were observed in DSC curves of myosin from smooth muscle. As pH and ionic strength increased, thermal stability of whole muscle decreased. Smooth muscles were more affected than striated muscles. The pH increment significantly affected ΔH of whole smooth muscles. ΔH significantly decreased when ionic strength increased to 0.5 in both types of muscle (Paredi et al. 1998). DSC curves of both striated and smooth whole muscles of scallop showed two transitions, Tmax 55.0, 79.2 °C and Tmax 54.7, 78.7 °C, respectively. The pH increase (5.0 to 8.0) significantly decreased ΔH of whole striated muscles. Significant decreases in ΔH were also observed in DSC curves of smooth muscles at pH 8.0. ΔH significantly decreased when ionic strength increased from 0.05 to 0.5 in both types of muscle. Striated muscles were affected more than smooth muscles by changes in the chemi- cal environment (Paredi et al. 2002). Three major endothermic peaks at 50, 57 and 74 °C were found in the DSC curve of the mantle of cuttlefish (Sepia esculenta). The first and second peaks mainly corresponded with the denaturation of myosin and collagen. The third peak was that of actin, which was almost native up to 63 °C, whereas the other proteins had  Differential scanning calorimetry 185 been completely denatured below 63 °C (Mochizuki et al. 1995a, b). Comparable results were reported for Sepia pharaonis (Thanonkaew et al. 2006). They found three endothermic transitions, with Tmax values of 49.8, 59.8 and 74.7 °C in the head portion, and three in the mantle portion with Tmax values of 50.3, 60.3 and 78.8 °C, corresponding to the thermal denaturation of myosin and paramyosin, connective tissues and actin, respectively. It was concluded that the thermal stability of an individual portion varied, depending on cuttlefish portions. In frozen and thawed freshwater prawns, the onset and peak melting temperatures corre- sponding to myosin denaturation, as well as ΔH of prawn muscle, decreased after freezing– thawing treatments (Srinivasan et al. 1997a). There were no significant differences in the thermal properties of prawns with changes in the rate of freezing. However, the thermal prop- erties were influenced by the rate of thawing. Rapid thawing resulted in a lower thermal stabil- ity of prawn proteins compared with slow or moderately fast thawing methods. Keeping prawn shells intact or not intact during freezing–thawing did not alter the thermal properties of the prawn proteins. Fresh prawns were subjected to five freeze–thaw cycles (−29 °C to 22 °C). ΔH decreased from 16.6 J/g (fresh) to 13.5 J/g after one freeze–thaw cycle with minor changes thereafter (Srinivasan et al. 1997b). The influence of protein content (25, 35 and 40%) in the feed given to blue shrimp on their thermal stability was investigated (Rivas-Vega et al. 2001). DSC curves showed three transition peaks, with Tmax values of 52, 72 and 86 °C. An influence of feed was not obvious. When fish (blue marlin, saury and skipjack) and shellfish (scallop and prawn) meat were compared for their thermal properties, three main endothermic peaks were displayed in the DSC curves (Uddin et al. 2001). Values of Tmax for myosin and sarcoplasmic proteins were approximately similar in both fish and shellfish meats, whereas that for actin was significantly higher in shellfish compared with fish meat. From our recently performed DSC measurements on deepwater rose shrimps (Parap- enaeus longirostris) caught in Turkey, it became obvious that frozen/thawed muscle of shrimp exhibited three peaks at 33.4, 50.4 and 57.9 °C, respectively. Pre-heating of samples to different temperatures in the range 30–70 °C caused the following changes in the DSC curves: at 40 °C the first peak disappeared, at 50 °C the second peak disappeared additionally, and at 70 °C no peak was detectable. However, in the range 50–65 °C, an additional peak at 73 °C became visible. A comparison of DSC curves taken from deepwater rose shrimp with those of black tiger shrimps (Penaeus monodon) farmed in Vietnam and white shrimps (P. vannamei) farmed in Ecuador revealed that the values of Tmax of the first peak were different, at 40 and 45 °C, respectively. This can be seen as an indication that species are possibly more responsible than environmental temperature for thermal stability of muscle proteins of shrimp. Thermal stability of muscle proteins from black tiger shrimp and from white shrimp were compared by DSC (Sriket et al. 2007). Two major peaks were obtained, corresponding to myosin and actin peaks. The two shrimps had similar Tmax and ΔH values of the first peak, suggesting that myosins of both shrimp muscles had similar temperatures and energies required for denaturation. Tmax of the second peak, representing actin of black tiger shrimp, was lower than that of white shrimp. However, no differences in ΔH of actin were found between the two species. This result revealed that the actin of white shrimp meat was more likely to resist thermal denaturation than that of black tiger shrimp meat. In shark muscle during heating, the following changes measured by DSC were assumed (Chen 1995): (1) changes in conformation of myosin molecules including solubilisation and 186 Fishery Products: Quality, safety and authenticity denaturation of myosin tails might occur at a low temperature (30–43 °C), corresponding to the low endothermic peaks; (2) at higher temperatures (47–57 °C), the head portion of the myosin molecule might project from the filament to enable more interactions among head portions; and (3) further interactions between myosin and actin could then form the actomyosin complex. In DSC analysis of small hammerhead shark (Sphyrna levini) muscle during cold storage at 5 °C, an exothermic peak within 25–45 °C and a low-temperature endothermic peak (LTEP) around 35 °C were observed after 8 and 56 hours, respectively (Chen et al. 1996a). The disappearance of LTEP accompanied the increase in the peak area at 61 °C, which was considered attributable to the denaturation of actomyosin complex. The thermal stability of thresher shark (Alopias pelagicus) muscle decreased during frozen storage at −18 °C (Chen et al. 1996b). The exothermic peak between 30 and 40 °C observed for the unfrozen muscle and the LTEP disappeared in the DSC pattern of muscle stored for 150 days. The longer the fish chunks were stored, the sooner the LTEP or endothermic peak around 50 °C disappeared and the endothermic peak at around 62 °C appeared. During frozen storage of silvertip shark (Carcharhinus albimarginatus), it was observed that the exothermic peak at around 45 °C visible for both fresh and 7-day frozen- stored muscle disappeared in the muscle stored longer than 14 days. Tmax of the endothermic peak of around 57 °C shifted to a lower temperature, and ΔH of muscle diminished with storage time. This revealed that the thermal stability of shark muscle decreased for the duration of storage time (Chen 1996). The DSC pattern of different shark meat (catsharks, Scyliorhinus spp., smoothhounds, Mustelus spp., liveroil sharks, Galeorhinus spp.) showed two main endothermic peaks and additionally a smaller one at lower temperatures. Skin was characterised by a pronounced peak that can be attributed to collagen. Additionally, DSC measurements were taken on previously heat-treated shark meat and skin (smoothhounds). Peaks disappeared gradually in the DSC curves taken on meat with increasing temperature. In skin samples the collagen peak at around 48 °C disappeared completely after heating to 45–50 °C, whereby after heat treatment to 50 °C a new small peak appeared at a lower temperature (around 28 °C), which resulted probably from denaturation of collagen to gelatine (Schubring 2007). Figure 8.4 displays the DSC curves of several invertebrates and shows the species-specific pattern. 8.4.3 DSC measurements on connective tissue and collagen In Japan, a great amount of fish scales is produced in sardine-processing factories and has potential as an important collagen source. The DSC curve of soluble collagen obtained from sardine scales indicated one peak, with Tmax at about 44 °C. This denaturation temperature was about 10 °C lower than that of pig collagen gel and is therefore interesting for food application (Nomura et al. 1996). Isinglass, a substance used to clarify alcoholic beverages, is derived from the swim bladder of certain tropical fish and consists predominantly of col- lagen. It exists as a rod-like triple helical molecule and is thermally labile. A Tmax of 29.8 °C and ΔH of 58.1 J/g were measured by DSC (Hickman et al. 2000). Collagens of skin and bone from bigeye snapper were classified as type I collagen. An endothermic peak, with Tmax at 31.0 and 31.5 °C, was observed for collagens from the skin and bone rehydrated in water, respectively. For collagens rehydrated in acetic acid, Tmax shifted to lower temperatures, 28.7 and 30.8 °C for collagens from skin and bone, respectively (Kittiphattanabawon et al. 2005).  Differential scanning calorimetry 187 –5.8 Scallop –6.0 –6.2 Shrimp –6.4 Squid –6.6 –6.8 ↑ Exo 25 30 35 40 45 50 55 60 65 Furnace temperature (°C) Figure 8.4 DSC curves of several invertebrates (scallop, Patinopecten spp.; shrimp, Parapenaeus longirostris; squid, Todarodes sagittatus). Skin collagen from bigeye snapper has high thermal stability compared with those reported for some cold-water fish species (Jongjareonrak et al. 2005). The effect of frozen storage (−10 and −30 °C), formaldehyde and fish oil on collagen, isolated from cod muscle, was investigated (Badii and Howell 2003). DSC showed a highly cooperative transition at 28.2 °C for isolated collagen. Changes in the thermodynamic properties of collagen were observed on frozen storage at −10 °C compared with the control at −30 °C because of changes in structure. In the presence of formaldehyde, there were no changes in the DSC collagen transition; however, in the presence of fish oil, there was an increase in enthalpy and an extra peak was observed at 44.6 °C, indicating collagen–fish oil interaction. Interaction of gelatine obtained from the skin of North Sea horse mackerel (Trachurus trachurus) with egg albumin proteins was investigated (Badii and Howell 2006). Horse mackerel gelatine solutions of 3, 5, 7 and 10% w/w in distilled water denatured at Tmax 14.7 °C, 14.7, 15.1 and 15.0 °C, which were not significantly different; however, ΔH values were. The samples were heat–reversible, with minor changes in Tmax and ΔH on a second scan of each gelatine sample confirming that gelatine undergoes a helix to coil transition on heating and on cooling refolds, recovering most of the helical structure. DSC curves of egg albumin showed three transitions, which were not reversible. In the mixture of 3% gelatine and 10% egg albumin, gelatine showed one cooperative transition, with Tmax 15.0 °C and ΔH 1.5 J/g. Even in the presence of egg albumin, this transition was reversible. 188 Fishery Products: Quality, safety and authenticity Gelatines were prepared from the skins of the tropical fish, sin croaker (Johnius dussu- meiri) and shortfin scad (Decapterus macrosoma), and compared for their thermal stability with bovine gelatine. The values of Tmax of gelatine gels were 28.9, 24.6 and 18.5 °C respec- tively for bovine, shortfin scad and sin croaker gelatines. The melting point of bovine gelatine was significantly higher than that of the other gelatines. These melting points were far higher than those reported for cod skin (Cheow et al. 2007). 8.4.4 Heat-induced gelation process Heat-induced gelation of surimi, an intermediate product produced by repeated washing of minced fish and mixing with cryoprotectants to extend its frozen shelf life, is an important step in the manufacture of a variety of surimi-based seafoods such as kamaboko, fish meat gel, and crab and other shellfish analogues. Heat-induced gelation of surimi is a complex physicochemical process involving structural and functional changes of myofibrillar pro- teins. DSC measurements were an obvious application for investigating these processes. Arrowtooth flounder myosin was found to undergo a multistage denaturation process, as characterised by an endothermic trough and peaks. Tonset was observed at 25 °C whereas Tmax was seen at 36 °C with one transition peak detected at 30 °C. This indicates that myosin of arrowtooth flounder is highly unstable to heat (Visessanguan et al. 2000). To investigate how proteolysis affects heat-induced gelation, papain was added to arrowtooth flounder myosin. This significantly decreased the enthalpy required to induce myosin denaturation without significant changes in Tonset and Tmax. Thermal denaturation kinetics indicated decreases in both activation energy and the rate of myosin denaturation (Visessanguan and An 2000). DSC curves of silver hake and mackerel surimi showed three endothermic peaks. When starch was added to surimi samples, an endothermic peak having a large area at a temperature of about 70 °C was observed, which overlapped the third actin transition. No significant shifts in the endothermic peaks of myofibrillar proteins were detected with increasing starch content. Transition temperatures for the starch–surimi system were higher than those for the starch–water system. There were deviations in the apparent heat capacity function calculated from DSC measurements in surimi samples containing starch. These are attributed to gelatinisation of starch and modification of water structure (Belibagli et al. 2003). Protein structural changes during preparation and storage of surimi investigated by DSC revealed a loss of myofibrillar proteins from surimi after three washing cycles and indicated greater protein stability in surimi compared with minced fish (Moosavi-Nasab et al. 2005). The use of polysaccharide gum such as hydroxypropylmethylcellulose in horse mackerel surimi as a possibility to reduce fat content resulted in variation of thermal stability (Chen et al. 2005). Medium-grade Alaska pollock surimi was used to investigate the effects of functional protein additives on calorimetric properties. The myosin peak temperature was shifted to higher values with addition of protein additives. These protein additives appeared to delay denaturation (unfolding) of fish proteins. Protein additives reduced the enthalpy of endothermic peaks. The reduction in enthalpy was possibly due to increased protein aggregation enhanced by protein additives (Park 1994). The thermal denaturation of tilapia (Oreochromis nilotica) surimi was shown to occur through three independent processes, and the temperatures at which these processes took place were 57.1 °C, 61.6 °C and 65.7 °C.  Differential scanning calorimetry 189 Addition of 0.2% of carrageenan raised the gelatinisation temperatures of tapioca and modi- fied waxy maize starches by 8 °C and 4 °C, respectively. However, it decreased the reaction enthalpy of waxy maize from 101.1 to 10.4 cal/g, and tapioca from 184.1 to 4.4 cal/g. The addition of starch and carrageenan to surimi was investigated by DSC. It was observed that for the surimi/tapioca and surimi/tapioca/carrageenan, the transition temperature increase was 20 °C compared with pure surimi (Barreto et al. 2000). Mixtures of κ- carrageenan plus other hydrocolloids (locust bean, guar, xanthan, í-carrageenan, sodium carboxymethylcellulose, and sodium alginate) were examined for their effects on the thermal behaviour of heat-induced gels made from washed blue whiting mince. DSC revealed faint interactions for the mixtures of κ-carrageenan with locust bean and with xanthan, and weakly synergistic gelling effects between the last two hydrocolloids. The blend of κ-carrageenan with sodium alginate exhibited thermally strong synergistic interactions, but no particular effects were induced on corresponding functional properties (Perez-Mateos et al. 2001). Changes in thermal properties of ribbonfish (Trichiurus spp.) meat during dif- ferent periods of ice storage were investigated (Dileep et al. 2005). The DSC profile of fresh ribbonfish meat revealed transitions at 33.2 °C, 48.9 °C and 61.0 °C, indicating the denatur- ation temperature of different protein fractions. The gelatinisation temperature of tapioca starch solution was found to be in the range 60–65 °C, and for cornstarch 67–70 °C. The viscoelastic properties of ribbonfish meat were altered significantly, both due to the addition of starch and ice-storage period (Dileep et al. 2005). DSC was used to study the effect of fish protein, salt, sugar and monosodium glutamate (MSG) on gelatinisation of tapioca and sage starches in fish cracker mixtures. One endothermic transition was observed for fish- starch mixtures (10–90% wet fish) if the moisture content was more than 61%. The effect of the salt on the starch gelatinisation was greater than sugar and MSG. Sugar and MSG addition to the mixture had little effect on gelatinisation of starch in the system. Two per cent salt increased the gelatinisation temperature by 4–5 °C. Tonset and Tmax increased with increases in fish content in fish-starch mixtures but the conclusion temperature (the temperature at which the DSC signal ceases to deviate from the baseline) remained relatively constant. Increases in fish content also narrowed the gelatinisation temperature ranges (Cheow and Yu 1997). 8.4.5 Antifreeze activities Antifreeze glycoproteins originating from fish were analysed for their activities by DSC. These proteins prevent the growth of ice crystals in the supercooled organisms. In polar fish, antifreeze glycoprotein consists of eight glycoproteins, sequentially numbered based on the mobility in polyacrylamide gel electrophoresis. DSC revealed that the low molecular mass glycoprotein 8 was sensitive to cooling rate, whereas the high molecular mass glycoproteins 1–5 were not. DSC curves revealed an initial shoulder in the exotherm direction upon cooling, which correlates with observed c-axis ice growth. DSC further revealed that glyco- protein antifreezes have a linear increase in thermal hysteresis or antifreeze activity with a decrease in sample ice content (Hansen et al. 1991). Recently, it was shown that the smaller antifreeze glycoproteins 7 and 8 from Antarctic fish showed reduced levels of inhibition of ice growth, as indicated by the absence of an initial exotherm and the absence of a lag at the start of each run (Ramløv et al. 2005). 190 Fishery Products: Quality, safety and authenticity The cryoprotective properties of proline in cod muscle were studied during freezing to − 60 °C and subsequent heating to 10 °C. No exothermic or endothermic transitions due to the crystallisation of proline were observed, suggesting that proline has the ability to stay in solution when the freezable water fraction of cod muscle was converted to ice. Therefore, proline may represent a promising ingredient as a cryoprotective in fish products (Rasmussen et al. 1997). Protein denaturation during frozen storage at −18 °C for 16 weeks was studied in jack mackerel (Trachurus murphyi) actomyosin. The cryoprotective effect of different additives was evaluated at a level of 8% (w/w): sucrose/sorbitol (1 : 1), maltodextrin 25 DE, milk whey and sodium lactate. DSC curves showed two endothermic transitions with Tmax at 46.8 °C and 68.9 °C assigned to myosin and actin, respectively. The best cryoprotective effect was achieved with sucrose/sorbitol and maltodextrin 25 DE. These additives showed Tmax and ΔH values for myosin and actin significantly higher than the control (Dondero et al. 1996). The antifreeze activities of saccharides that consisted of glucose measured by DSC were higher than those of the other food components. In salts, those that possessed high ionic charge had high antifreeze activities. In water-soluble amino acids, a few amino acids (threonine, arginine and proline) that formed no eutectic mixture above −20 °C had especially high antifreeze activities (Mizuno et al. 1997). A DSC heat denaturation study on the effects of various maltodextrins and sucrose on protein changes in minced blue whiting muscle during frozen storage at −10 and −20 °C revealed that all maltodextrins slowed the decreases in ΔH ascribed to myosin and actin, making evident a noticeable effectiveness against protein denaturation, especially at −20 °C. Sucrose was as effective as maltodextrins at −20 °C, but was the least effective treatment at −10 °C. Significant correlations between both ΔH and either protein solubility or formaldehyde production were found at each storage temperature (Herrera et al. 2001a, b). Unlike conventional surimi processing, a novel method of fish protein isolate chemically induces denaturation by altering pH during the process. The new process for fish protein isolate, where protein structures are intentionally unfolded/refolded by pH-shift, is almost ready for commercialisation. However, it is unknown whether cryoprotectant will be required or not. This process has been investigated to improve gelation properties and yield using acid- or alkali-aided treatment. The aims were to determine the effect of pH on fish protein isolate during frozen storage (pH 5.5 and pH 7.0) and the effect of cryoprotectant on the functional properties of the fish protein isolate. The DSC curve of Pacific whiting conven- tional surimi contained four endothermic transitions, with Tmax of 35.4 °C, 41.2 °C, 51.1 °C, and 68.8 °C, respectively. All alkali-treated protein isolates, with cryoprotectants with and without freeze/thaw treatments, showed three endothermic peaks, with Tmax about 33.5 to 34.7, 46.2 to 47.8 and 66.5 °C to 68 °C, respectively. Alkali-treated protein isolates kept frozen at pH 5.5 were relatively less stable than those stored at pH 7.0. Actin was highly sensitive to the pH-shift method, particularly samples without cryoprotectants. DSC curves of actin appeared at Tmax of 66–68 °C with very small endothermic transition (10–15 °C) Fresh chilled fish Vacuum Shewanella putrefaciens, Vibrionaceae, Shewanella putrefaciens, Photobacterium phosphoreum, Lactic (0–5 °C) Photobacterium acid bacteria Modified Photobacterium, Shewanella putrefaciens, Photobacterium phosphoreum, Lactic acid bacteria atmosphere Pseudomonas spp. Cold–smoked fish Vacuum Pseudomonas spp., Lactic acid bacteria (Lactobacillus, Lactococcus, Carnobacterium), Enterobacteriaceae, Acinetobacter, Enterobacteriaceae (Serratia spp., Hafnia alvei, Enterobacter Staphylococcus spp., Shewanella spp.), Photobacterium, Brochothrix thermospacta putrefaciens, Vibrionaceae, Photobacterium Hot-smoked fish Vacuum Pseudomonas spp., Lactic acid bacteria (Carnobacterium) Enterobacteriaceae, Staphylococcus spp., Lactic acid bacteria Microbiological methods ‘Gravad’ fish Vacuum Data not available Lactic acid bacteria (Lactobacillus, Leuconostoc, Weissella, Carnobacterium) Semi-preserved Lactic acid bacteria Lactic acid bacteria (Lactobacillus) marinated fish Lightly salted and Modified Data not available Lactic acid bacteria (Lactobacillus, Enterococcus, Lactococcus) fermented fish atmosphere Sources: Huss 1995; Gram and Huss 1996 319 320 Fishery Products: Quality, safety and authenticity the fish (brining or salting by injection) and smoking at temperatures not higher than 28°C. Among the countries producing cold-smoked salmon, France is the leading country followed by Denmark, Germany and the United Kingdom (Cardinal et al. 2004). 15.2 General aspects of microbiological methods The aims of microbiological examination of fish and fish products are to evaluate the hygienic quality of fish and to detect possible pathogenic microorganisms. They consist of the measurement of total aerobic bacteria, spoilage bacteria and pathogenic bacteria (Huss 1995). The food microbiologist can choose from a wide variety of conventional microbiological and new molecular biological methods to analyse fish and fish products. Traditional microbiological methods require much manual labour, are time-consuming and costly. They require skills in the execution and interpretation of the results (Huss 1995). Furthermore, these metho