TECHNICAL REPORTS SERIES No. 124 Radurization of Scampi, Shrimp and Cod JOINT FAO/IAEA DIVISION OF ATOMIC ENERGY IN FOOD AND AGRICULTURE ié) INTERNATIONAL ATOMIC ENERGY AGENCY, VIENNA, 1971 RADURIZATION OF SCAMPI, SHRIMP AND COD TECHNICAL REPORTS SERIES No. 124 RADURIZATION OF SCAMPI, SHRIMP AND COD by G. HANNESSON and B. DAGBJARTSSON Icelandic Fisheries Laboratories Reykjavik, Iceland REPORT OF A PROJECT ORGANIZED AND SUPERVISED BY THE JOINT F AO/IAEA DIVISION OF ATOMIC ENERGY IN FOOD AND AGRICULTURE INTERNATIONAL ATOMIC ENERGY AGENCY VIENNA, 1971 RADURIZATION OF SCAMPI, SHRIMP AND COD IAEA, VIENNA, 1971 STI/DOC/lO/124 Printed by the IAEA in Austria April 1971 FOREWORD In January 1968 an agreement was reached in Vienna by representatives of the Governments of the United States of America, Iceland and the Inter- national Atomic Energy Agency (IAEA) to undertake a survey project on the use of ionizing radiation for extending the storage life of seafoods. The United States Atomic Energy Commission (USAEC) provided an irradiator for a period of eighteen months. The irradiator, originally used on the US Bureau of Fisheries exploratory vessel M.V. Delaware, was furnished with a new cobalt-60 radiation source at the Brookhaven National Laboratories (BNL). It was assembled and installed on the ground floor of the Icelandic Fisheries Laboratories (IFL), Reykjavik, under the super- vision of Mr. B. Sylvester of BNL. The activity of the source was approxi- mately 35 000 Ci. The project was started in July 1968. The IFL furnished laboratory facilities, rawmaterial, manpower and other services. The IAEA granted fellowships for training two scientific staff members of the IFL in the ir- radiation of foods and the operation of irradiation facilities. It was also agreed that the IFL would accept and provide facilities for IAEA Fellowship holders, from various countries, who would participate in the project as scientific co-workers. The average stay was for two months. The USAEC provided a fisheries irradiation expert, Mr. J.D. Kaylor of the Bureau of Commercial Fisheries, Gloucester, Mass., who stayed at the IFL from 16 June to 16 July 1968. Under his supervision the ground- work was laid for satisfactory radiation safety procedures in co-operation with Dr. G. Jónsson, Director of the Icelandic Radiological Health Labora- tory. Mr. Kaylor was also occupied in training and familiarizing the scien- tific staff members in radiation calibration and dose determinations. The main objective of the survey was to demonstrate whether radiation preservation is practical under the type of conditions that exist in the fishing industry and trade in Iceland. As the domestic market in Iceland is very limited, it is important to export as much of the seafood catch as possible. Most of the catch is salted, dried or frozen. Nevertheless a considerable quantity, amounting to 30 000 - 40 000 tonnes, of iced fish such as whitefish (e.g. cod and haddock) and herring is shipped annually to the United Kingdom and Continental markets, where it is sold in the fresh state. Because some of this iced fish arrives in an unsaleable condition, it seemed desirable to determine whether the storage life of fresh Icelandic seafoods could be extended by radiation preservation beyond what is attained by icing. No attempts as yet have been made to market fresh, iced lobster, shrimp and other shellfish because of lack of satisfactory preservation techniques. The investigation was concentrated on one species of fish, cod, and two crustacean species, scampi (Norway lobster tails) and deep-sea shrimp. The results showed that the storage life of cod fillets at 0°-l°C, ir- radiated at a dose level of 2 X 105 rad, could be extended by a factor of about 3, namely up to 19 days for trawl cod and 24 days for line cod. The market life of blanched shrimp and scampi, irradiated at a dose level of 1 X 105 to 2 X 105, could be increased to about 6 weeks when stored at 0°-l°C; this is about twice the market life for unirradiated specimens. Clearly these results could have commercial importance. The authors of this report express their gratitude to the organizations who enabled the work to be undertaken, and to the many scientists who participated in the project. CONTENTS PART I. RADURIZATION OF NORWAY LOBSTER TAILS (SCAMPI) 1 1. INTRODUCTION : 1 2. MATERIALS AND METHODS 2 2.1. Processing methods 2 2.2. Analytical methods for storage life determination 3 3. RESULTS 5 3.1. Results of preliminary experiments 5 3.2. The effect of processing treatments on number of surviving micro-organisms (bactericidal efficacy) 27 3.3. Results of storage tests at 0° - 1°C and 5° - 6°C on the effect of various treatments on the total bacterial count (TBC), sensory evaluation (T-tests) and volatile acid number (VAN) 27 4. DISCUSSION 29 4.1. The radiation dose 29 4.2. Sensory evaluation (T-test) 29 4.3. Volatile acid number (VAN) 30 4.4. Bacteriological aspect of the study 31 4.5. Comparison of factors influencing storage life 32 4.6. Possible use of irradiation for processing and preservation of lobster 33 5. SUMMARY AND CONCLUSIONS 34 PART II. RADURIZATION OF DEEP-SEA SHRIMP 35 6. INTRODUCTION 35 7. MATERIALS AND METHODS 35 7.1. Materials 35 7.2. Methods 43 8. RESULTS 46 8.1. Bacteriological determination (TBC) 46 8.2. The effect of various processing treatments and irradiation on storage life 53 9. DISCUSSION . 56 10. SUMMARY AND CONCLUSIONS 59 PART III. RADURIZATION OF WHOLE COD AND COD FILLETS.. 61 11. INTRODUCTION 61 12. MATERIALS AND METHODS 62 12.1. Raw material, origin and preparation 62 12.2. Packaging 63 12.3. Storage 63 12.4. Irradiation dose 63 12.5. Sensory evaluation (O-test) 64 12.6. Chemical tests 65 12.7. Bacteriological determination (TBC) 65 13. RESULTS 66 13.1. Results of O-test 66 13.2. Results of chemical tests (VAN and TMA) 69 13.3. Bacteriological determination (TBC) 82 14. DISCUSSION 86 15. SUMMARY AND CONCLUSIONS 90 ACKNOWLEDGEMENTS 92 REFERENCES 92 PART I RADURIZATION OF NORWAY LOBSTER TAILS (SCAMPI) 1. INTRODUCTION The project began in the midsummer of 1968 after installation, testing and calibration of the irradiator [1] . At that time of the year Icelandic fisheries are based mainly on white- fish and herring. However, this is also the high season for lobster. The lobster season lasts from June until September. The main whitefish season (cod, haddock, etc.) is from January until May. It was therefore felt logical to start the irradiation project with the lobster, which was readily available. The species of lobster which lives in the waters off Iceland is the Norway or Dublin lobster, whose scientific name is Nephros norvegicus. Norway lobsters and particularly the shelled tail-meats have become known as scampi. The lobster is found in the Faeroes and off Iceland, it ranges from the coasts of Norway, Scotland and Ireland to the Mediterranean. The lobster is fished commercially in Iceland using rather small boats by means of a specially designed light lobster trawl. On board the boats the head and carapace, with claws and legs attached, is twisted off and dis- carded leaving only the unshelled tails to be iced until landed. The amount of meat in the claws is very small and at present is not salvaged. Also the separation is carried out because the digestive glands in the dead, whole lobster would rapidly break down the edible flesh. The use of refrigerated seawater for preservation of lobster tails has not given good results, pri- marily because of difficulty in controlling the proper ratio of ice to sea- water. The iced lobster tails are processed as soon as possible, i.e. washed, degutted by a mechanical device, graded as to size, wrapped in parchment and packed in 5-lb wax boxes, and frozen in plate freezers. This product is the highest priced and most sought after. Deformed, broken and dis- coloured tails are panfrozen to be deshelled during off-season, and fetch a substantially lower price. Lobster fishing is a new branch of the Icelandic fishing industry and is localized on the southwest coast. The mean annual catch during 1960-66 was about 3000 metric tons of whole lobster. Prime lobster tails are sold wholesale for $3.55 per kg after packaging and freezing. Compared with other seafood products the price is very high and obviously it is essential that product losses be kept at the absolute minimum. Lobsters [2] have a relatively short storage life compared with other iced fish products. The chief spoilage patterns can be characterized as follows: (1) black colour (melanosis) formation, also known as "black spot"; (2) rapid and high ammonia and trimethylamine (TMA) production; and (3) microbial spoilage [3] . Black colour formation is caused by auto-oxidation of certain chromo- genes of the phenolamine type [4] which in turn are caused by enzymatic breakdown of proteins. 1 Measures to prevent the formation of black colour include both chemical and physical means. Chemicals such,as ascorbic, citric and tartaric acids, sulphites and ordinary salt have been used as dips or incorporated in ice[3,4] . One of the most effective and simple ways to prevent melanosis is by blanching in boiling water. By blanching is implied dipping the product in boiling water for a specified short time. The term precooking is also used in this connotation, particularly for shrimp. No significant data are available which account for deteriorative changes causing spoilage in raw lobster. There are, however, several indications that they follow the general pattern for crustaceans [3, 5] . Like other crustaceans, lobsters are characterized by a relatively high content of mono-aminonitrogen.