Preservation of Marine Products by Salting and Drying
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PRESERVATION OF MARINE PRODUCTS BY SALTING AND DRYING by NORYATI ISMAIL (M.Sc., University of Nottingham) A thesis submitted in fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY UNIVERSITY OF NEW SOUTH WALES March 1990 UNIVERSITY OF N.S.W. 2 1 MAk 1991 LIBRARY ABSTRACT Dried, salted morwong, shark and sardine salted in saturated brine at 30°C and dried at different temperatures under ambient RH were prepared. Dried squid was prepared without salting. Salt uptake was very rapid and highest in shark followed by morwong and sardine. Moisture loss was highest in sardine followed by shark and morwong. Squid attained the highest drying rates amongst all the species and at 50°C its rate was the highest followed by shark, morwong and sardine. A drying temperature of 50°C gave a compromise between product quality and drying rates. Lightly salted products were significantly (p < 0.01) prefe^ed in all species. Products dried at lower temperatures were significantly more acceptable (p < 0.01) for shark and sardine but not for morwong and squid. Products salted for 8h (morwong and sardine) 4h (shark) and non-salted (squid) and dried at 50°C were used for storage studies. Storage at 5°C was superior to that at 25°C or 37°C in terms of product appearance, browning, rancidity, moisture loss, product texture and rehydration behaviour. The effects of salting, drying and storage on the protein properties were demonstrated by decreased protein solubility in KCl and SDS + B mercoptoethanol, disappearance and lost intensity of some bands in the IEF pattern of water soluble proteins in all the species. However, changes in in vitro protein digestibility and amino acid contents were not significant. pH declined during salting in all the species. TVB and TMA contents in shark decreased but increased initially in sardine and morwong with subsequent decline during further salting. During drying TVB and TMA rose increasingly (p < 0.01) with increasing temperature of drying, increases in TVB and TMA were also observed on storage (p < 0.01). Shark, morwong and sardine had two endothermic peaks in their DSC thermograms, at 146°-50°C (myosin) and 72°-80°C (actin). Squid had three endothermic peaks at 37°, 43° and 80°C. The first peak disappeared after 8-12h salting and Tmax of peak II (actin) in shark, morwong and sardine decreased as did peak area (i.e. A HQ) During drying, peak areas decreased and peaks broadened, to a greater degree with increasing drying temperature. Drying effects were more acute in shark and squid. These effects reflect denaturation of protein due to salt and higher temperature. SEM examination of the fish tissues showed the effects of disruption due to salting and the reduction in compactness due to drying. The composition of these products was comparable with that of some commercial products from South East Asia. Dried salted sardines were also produced from sardines stored for 0, 1 and 2 weeks at 5°C. Products from the stored sardines were found to be of inferior quality to those made from fresh fish. ACKNOWLEDGEMENTS I am greatly indebted to my supervisor, Prof. M. Wootton, Senior Lecturer for his advice, suggestions and guidance throughout the research period. Dr. Wootton has unselfishly given a lot of his time and energy especially during the preparation of the manuscript. I wish to express my gratitude to the Australian Development Assistance Bureau (ADAB) for the award of a scholarship and financial support during my stay in Australia. I thank Prof. R. A. Edwards, Head of School of Food Technology, University of New South Wales for allowing me the use of facilities and instruments. Lastly, this thesis is dedicated to my family for their support and encouragement. iv This thesis contains no material which has been accepted or submitted for the award of any degree or diploma in any university. Furthermore, this thesis is original and contains no material, published or written by another person, except where due reference is made in the text. (NORTATI ISMAIL) March 1990 (v) CONTENTS Page Abstract i Acknowledgements iv Declaration vi Table of Contents vii List of Tables viii List of Figures x List of Plates xxi List of Appendices xxiii CHAPTER 1 INTRODUCTION 1 1.1 Fish in Civilisation 1 1.2 World Production of Dried Fish 5 1.3 Wastage 8 1.4 The Project 10 CHAPTER 2 LITERATURE REVIEW 12 2.1 General Methods of Fish Preservation 18 2.2 Salting 18 2.2.1 The Ingredient 18 2.2.2 The Preservative Action 2.2.3 Methods of Salting 20 2.2.4 Salt Penetration 22 2.2.5 Salting Equilibria 23 2.2.6 Innovative Salting Techniques 24 vi Page 2.3 Drying Processes 24 2.3.1 Preservative Role of Drying 25 2.3.2 The Theory of Drying 27 2.3.3 Factors Affecting the Drying 31 Rate of Salted Fish 2.3.4 Innovative Drying Techniques 35 2.4 Chemical Properties of Salted Dried Fish 38 2.4.1 Volatile Bases 38 2.4.2 Moisture and Salt Content 45 2.4.3 Water Activity 49 2.4.4 Proteins 58 2.4.5 Lipids 70 2.4.5.1 Rancidity in Salted Dried Fish 72 2.5 Physical Attributes of Salted Dried Fish 75 2.5.1 Colour 75 2.5.1.1 Colour definition 76 2.5.1.2 Application to fish products 77 2.5.2 Microscopic studies 82 2.5.3 Thermal studies of fish 84 2.5.4 Reconstitution properties 90 2.6 Organoleptic Property of Salted Dried Fish 95 2.7 Packaging and Storage of Salted Dried Fish 100 CHAPTER 3 EXPERIMENTAL 106 3.1 Processing 106 3.1.1 Fish samples 106 3.1.2 Salting 106 3.1.3 Drying 107 3.2 Chemical Analysis 107 3.2.1 Moisture content 107 3.2.2 Salt (Sodium chloride) 107 3.2.3 Protein content 108 3.2.4 Fat content 108 3.2.5 Water activity (Aw) 109 vii Page 3.3 Solubility of Proteins 110 3.4 Digestibility of Protein by Pepsin 110 3.5 Isoelectric Focussing 112 3.5.1 Materials 112 3.5.2 Reagents 112 3.5.3 Sample preparation 113 3.5.4 Methods 114 3.5.4.1 Casting the gel 114 3.5.4.2 Moulding 114 3.5.4.3 Running the gels 114 3.5.4.4 Fixing and staining 115 3.6 Total Amino Acid Analysis 116 3.6.1 Materials 116 3.6.2 Reagents 116 3.6.3 Reagent preparation 117 3.6.3.1 Constant boiling HCl 117 3.6.3.2 Ninhydrin 117 3.6.3.3 Buffer A 118 3.6.3.4 Buffer B 118 3.6.4 Methods 118 3.6.4.1 Acid hydrolysis 118 3.6.4.2 Preparation for chromatography 119 3.6.4.3 Chromatographic conditions 119 3.7 Rancidity 120 3.8 Scanning Electron Microscopy 121 3.9 Colour 121 3-io Differential scanning colorimetry 121 3.10.1 Equipment and materials 121 3.10.2 Procedure 122 3.11 Reconstitution Properties 123 3.12 Sensory Evaluation 123 3.13 Storage Studies 124 3.14 Statistical Analyses 124 viii Page CHAPTER 4 RESULTS AND DISCUSSION 125 4.1 Processing of Fish 125 4.1.1 Morwong 125 4.1.1.1 Brining 128 4.1.1.2 Drying of morwong fillets 131 4.1.1.3 General remarks on the dried 134 products 4.1.1.4 Sensory evaluation of morwong 136 4.1.1.5 Chemical properties of salted 139 dried morwong 4.1.1.5.1 Effects of salting 139 4.1.1.5.2 Effect of drying on 149 morwong 4.1.1.6 Storage studies on morwong 157 4.1.1.6.1 Evaluation of stored 157 morwong 4.1.1.7 Chemical properties of stored 171 morwong 4.1.2 Shark 185 4.1.2.1 Chemical composition of shark 185 4.1.2.2 Salting of shark 187 4.1.2.3 Drying studies 188 4.1.2.4 Product quality 190 4.1.2.4 Sensory evaluation of the 191 dried product 4.1.2.6 Chemical changes of ^elf-ed 193 dried shark 4.1.2.6.1 Effects of salting 193 4.1.2.6.2 Changes to salted shark 199 during drying 4.1.2.7 Storage Studies on Shark 206 4.1.2.7 Evaluation of the product 207 4.1.2.7.2 Chemical properties of 213 stored dried shark ix Page 4.1.3 Sardine 223 4.1.3.1 Salting of sardines 225 4.1.3.2 Drying of sardines 226 4.1.3.3 Product quality 227 4.1.3.4 Sensory evaluation of dried sardines 229 4.1.3.5 Chemical properties of salted 231 dried sardine 4.1.3.5.1. Effects of salting 231 4.1.3.5.2. Effects of drying on 238 sardine 4.1.3.6 Storage studies 244 4.1.3.7 Chemical Properties of stored 267 sardines 4.1.4 Squid 267 4.1.4.1 Chemical composition of fresh squid 268 4.1.4.2 Drying of squid and product quality 268 4.1.4.3 Sensory evaluation: Acceptability 272 vs drying temperature 4.1.4.4 Chemical properties in dried squid 273 4.1.4.4 Storage studies on dried squid 281 4.1.4.5 Chemical properties of stored 287 dried squid 4.1.5 Salting and drying of aged fish 296 4.1.5.1 Effect of fish freshness on 297 salt uptake 4.1.5.2 Drying of the aged fish 301 4.1.5.3 Chemical properties of salted 301 aged fish 4.1.5.4 Product quality 318 4.2 Differential Scanning Calorimetry 322 4.2.1 Effect of salting on the thermogram of fish 327 4.2.2 Effects of drying on DSC thermogram of fish 335 4.3 Analyses of Commercial Dried Products 342 CHAPTER 5 CONCLUSION 345 REFERENCES 346 APPENDICES x LIST OF TABLES Page Table 1.1: Total world fish production and 6 disposition.