Fish Processing Technology In The Tropics (Espejo-Hermes) PDF

FISH PROCESSING TECHNOLOGY IN THE TROPICS (J. ESPEJO-HERMES) Chapter 1. INTRODUCTION DEVELOPMENT OF FISH PROCESSING TECHNOLOGY 1950’S  Freezing at sea  Chilling in chilled/refrigerated seawater in on-board fishing vessels  On-board processing into fillet blocks 1970’s  Meat-bone...

FISH PROCESSING TECHNOLOGY IN THE TROPICS (J. ESPEJO-HERMES) Chapter 1. INTRODUCTION DEVELOPMENT OF FISH PROCESSING TECHNOLOGY 1950’S  Freezing at sea  Chilling in chilled/refrigerated seawater in on-board fishing vessels  On-board processing into fillet blocks 1970’s  Meat-bone separator or deboner  Improvement of surimi and fish analogues manufacture 1980’s – 1990’s  No new major technologies introduced  Only consolidation and development of current ones 1.1 WORLD UTILIZATION (1985-1993)  Decrease in frozen fish quantity due to withdrawal of factory vessels and freezer trawlers from USSR  Amount of cured fish (salted, dried, smoked) and canned products declined due to shift from cured/canned fish to fresh fish 1.1.1 Southeast Asia  Traditional processing methods (drying, salting, fermentation and smoking) still practiced  Consumer preference to value-added products (frozen fillet, fish balls, etc.)  “Ready to heat and eat” fishery products are becoming in demand  Philippines is 2nd to Indonesia in cured fish production 1.1.2 Philippines  >7,000 islands  17,640 km coastline  290,000 km2 continental shelf area  2.5M km2 EEZ area including territorial waters  9,000 km2 freshwater bodies  5,000 km2 brackish water and swamplands  >2,000 species of fish, mollusk, crustaceans and echinoderms and other aquatic fauna and flora  Fish sauce(patis) and fish paste peak production in April and declines to October 1.2 NUTRITIVE VALUE OF FISH   Healthy due to fish oils (PUFA) or omega-3  Fish is low-calorie and low-fat edge  Good source of vitamins A and B complex and minerals such as iodine, fluoride, selenium and zinc  Oysters and mussels have very high levels of iron; higher than red meats. 1.2.1 Structure of fish and fish muscles  Fish are divided into classes  Cephalaspidomorphi – jawless fish like lampreys and slime eels  Chondrichthyes – cartilaginous fish (elasmobranchs) like sharks and rays  Osteichthyes – lungfish and bonyfishes(teleosts) 1.2.1.1 Structure of fish (bony and cartilaginous fish)  Main parts of a typical bony fish  Skeleton  Muscle tissues  Skin and fins  Viscera 1.2.1.2 Structure of fish muscles  Edible meat/portion is about 60% of whole weight  Muscle contains  myotomes (muscular tissue)  myocommata (connective tissue)  fat  90% white muscle (light or no pigment) – sprinting muscle for abrupt, fast movements  10% is red (dark) due to myoglobin pigment content – cruising muscle for slow continuous motion  Higher levels of lipids, hemoglobin, glycogen and most vitamins in dark muscle.  Myocommata contains mostly the protein collagen  Bony fish contains 3% collagen; cartilaginous fish contains 16%  Perimysium envelops the muscle bundle  Endomysium encloses muscle cell or fiber  Connective tissue protein constitutes 17% of the total protein in mammals. 1.2.2 Composition of fish  Important to food processor, nutritionist and consumer  Varies from species to species, individual to individual depending on age, sex, environment and season 1.2.2.1 Protein  Composed of building blocks- amino acids  16-22% high quality protein contained in most fish   Lysine and methionine – EAA lacking in cereal and root crop-based diets 1.2.2.2 Fat (lipids)  Ranges from 0.2-2.5% in fish  Rarely exceeds 5% in tropical species  80% of flesh is water and fat  Fish contains long chain fatty acids (14-22 carbon atoms0 which are highly unsaturated  Fish fat is rich in high-grade PUFAs (omega-3)  2 of the 7 omega-3 FA not found in beef and pork and vegetables  EPA(eicosapentaenoic acid)  DHA (docosahexaenoic acid)-brain growth and development  O-3 prevents heart disease by suppressing formation of blood clot  Effects of fish oils on human health  Decrease blood circulatory diseases  Decrease serum total cholesterol levels  Increase HDLP (high density lipoprotein) cholesterol 1.2.2.3 Vitamins  Varies from species to species  Red meat is rich in Vitamins:  A (retinol)  B1 (thiamine)  B2 (riboflavin)  B12 (cyanocobalamin)  D3 (cholecalciferol)  Skin contains more B1 (thiamine) and B2 (riboflavin) than in flesh.  Liver are rich in Vitamins A (retinol), D3 (cholecalciferol) and B3 (Niacin)  Mollusk and crustaceans are important sources of Vitamin B complex, mainly Vitamin B6 (pyridoxine) and B3 (Niacin)  Vitamin A prevents night blindness, promotes growth, reduces susceptibility to infections, dry skin and dry hair  Vitamin B group prevents mental depression, convulsions, irritability, anemia, nerve damage, skin rashes, tissue degeneration and weight loss  Vitamin D3 – peculiar to fish, assist in calcium metabolism 1.2.2.4 Minerals  Iodine – for thyroid function/ found rich in fish, seaweeds, mollusks and crustaceans  Fluorides in fish – protection against tooth cavities  Selenium – prevention of heart disease and possibly cancer  Fish are low in sodium 1.2.2.4 Other components   66-81% moisture content  Taurine –sulphonic AA–decreases total cholesterol in blood, brain fetal development Chapter 2. HANDLING OF FRESH (WET) AQUATIC PRODUCTS  Fish and aquatic products – most perishable commodities  Spoilage begins after death  Spoilage of fish – no single factor responsible/ combination of interrelated processes resulting to:  formation of hypoxanthine, trimethylamine…  dev’t of undesirable odors and flavors  softening of the flesh  loss of cellular fluid containing fat and protein 2.1 SPOILAGE OF FRESH AQUATIC PRODUCTS  fresh fish spoilage – mainly bacterial in nature aided by enzymatic activity  bacterial and enzymatic spoilage – temperature dependent  the higher the temperature, the faster the rate of spoilage  fatty fish spoil faster than lean fish  small spoils faster than large fish of same species  cold-water spoils faster than warm-water fish  round fish spoils faster than flat fish 2.1.1 Bacteria  flesh of live fish is sterile but normally present in surface slime, gills and guts  freshwater fish - mesophilic gram+ bacteria (Micrococcus, Bacillus and Coryneforms)  marine fish – psychrotrophic gram-negative genera (Pseudomonas, Alteromonas, Moraxella, Acinetobacter, Flavobacterium, Cytophaga and Vibrio)  > 4oC – reproduction and growth rates of bacteria generally increase  60oC – some bacteria remains active  Alteromonas putrefaciens, certain Pseudomonas, Vibrio and Aeromonas - the most active SSO gram-, psychrotrophic rods in chilled fish  Shewanella putrefaciens – SSO for the aerobic chill spoilage of temperate fishes  Bacterial spoilage does not start until the passage of rigor mortis.  Rigor mortis – progressive stiffening of muscle shortly after death. Starts from tail to head. May range from an hour to 3 days or more depending upon  Species, size, catching method, handling of fish, temperature, physical condition of fish  Any delay in rigor will prolong keeping time of the fish. 2.1.2 Enzymes  Present in muscle and gut  Initiate or speed up chemical reactions   At death, oxygen and energy production ceases  Glycolysis (glycogen breakdown) and degradation of energy rich compounds begins.  Self-breakdown or self-digestion (autolysis) occurs due to enzymes in gut and muscles resulting to weakening, softening and discoloration of fish tissues  Rate of autolysis can be retarded by keeping at low temperature just above freezing point  Enzymatic activity can be stopped by heating and can be controlled to a large degree by other methods (salting, drying, frying and marinating) 2.1.2.1 Muscle enzymes and their activity  Autolysis involves carbohydrates and nucleotides  ATP production stops  Rigor mortis develops at low ATP levels  Fish has lower glycogen than mammals so post-mortem(PM) pH is higher  Glycogen is degraded by glycolysis or by direct amylolytic hydrolysis  Glycolysis under PM conditions continues under anaerobic conditions resulting to lactic acid formation  Lactate formed reduces pH  PM lowering of pH causes decline in water-binding capacity of proteins because they are brought closer to their isoelectric point 2.1.2.2 Digestive enzymes and their activity  Ungutted fish is vulnerable to tissue degradation and may rupture within a few hours of capture 2.1.3 Chemical spoilage  Mainly occur during storage in ice or in frozen condition  Rancidity of lipids may involve lipid autolysis (enzymatic hydrolysis with free fatty acids, and glycerol as main product) and auto-oxidation (the reaction of unsaturated lipid with oxygen.  Auto-oxidation is generally more prevalent in aquatic products due to their higher degree of unsaturation than in other foods  Oxidative rancidity – results to rancid flavor and odor as well as discoloration  Denaturation of protein during frozen storage results to tough, dry and fibrous texture.  Darkening of red meat in fresh fish may occur due to change of myoglobin from bright red to red-brown nor dark brown in the cellular tissues 2.2 HYGIENE AND SANITATION  Hygiene science of good health, signifies cleanliness and freedom from risk of infectious disease  In foods and food processing – good quality and absence of poisoning hazard  Contamination with bacteria – major cause of fish flesh spoilage   Pathogenic bacteria can cause illness or even death  Fish should be kept clean and held at low (chilled) temperature 2.2.1 Cleanliness  Needed at every stage of fish handling and preparation  Clean – absence of visible dirt and unwanted matter  Cleaning – removal of soil, food residues, dirt grease or other objectionable matter  Sanitation or disinfection is required – cleaning can’t reduce # of microbes  Sanitation – process of reducing the # of living microorganisms in the plant to a level judged safe by public health authorities  Detergents and disinfectants or sanitizers – used in hygienic cleaning procedure  Detergents – loosen and help remove dirt  Sanitizer – kills actively growing microbes  Ideal detergents would be characterized by: o Good wetting capacity o Ability to remove soil from surfaces o Power to emulsify o Capacity to hold material in suspension o Good rinsing property o Non-corrosive o Compatible with other materials o Quick and complete solubility o Dissolving action on food solids o Germicidal action o Complete water softening power o Non-toxic o Economical to use  Properties of good sanitizer or disinfectant o Effective germicide o Easy to dissolve in water o Low level of toxicity o Stable in concentrated form o Does not significantly corrode metal and plastic o Effective at low concentrations unaffected by water conditions o Safe to health in both concentrated and diluted form o Deodorizes o Compatible with cleaning compounds o Of low persistence  Sanitation and disinfection can be made by physical treatment o Heat o UV radiation  Chemical disinfectants in food industry o Chlorine and chlorine compounds  o Iodophors o Quaternary ammonium compounds o Ampholytic compounds o Peracetic acid o Hydrogen peroxide  All equipment, tools and premises must be kept clean by using detergents and sanitizers 2.2.2 Personal hygiene  Good personal hygiene can be practiced through: o Bathing daily o Using appropriate deodorants o Washing hair at least weekly o Keeping nails clean and trimmed o Wearing clean uniforms and clean underclothing o Using a hair net or cap and paper masks over nose and mouth when on duty o Preparing for work in a systematic fashion so that the individual and his clothing are clean at the time he starts to work  Washing of hands is more important in the prevention of contamination in foods  Washing should be done after: o coughing and sneezing o Visiting the toilet o Smoking o Handling equipment and other items o Handling raw fish o Handling garbage or soiled materials o Handling money 2.3 WAYS OF PREPARING FISH  Drawn fish (Gutted) – eviscerated/ entrails removed  Dressed fish – scales, viscera, fins, head and tail removed  Steaks – cross-section slices of a large, dressed fish (usually 2-3 cm thick)  Fillet - meaty sides of fish removed from the backbone and ribs of the fish o Block/butterfly/double – 2 sides joined together o Cross-cut fillet – fillet from flatfish taken from each side as a single piece o Quarter-cut fillet – cross-cut fillet taken into 2 pieces o Single fillet – one side of fish  Sticks and portions – small elongated chunks (rectangles) of uniform size and thickness cut from the meaty portion of the fish 2.4 FILLETING OF FISH   Fish that have been chilled and hence have just passed the rigor (stiffening) condition will be the most suitable raw material for filleting  Good quality fillets can also be obtained from frozen thawed fish, which have been frozen within 2-3 days of death (storage being near 0oC)  In this case, the fillets produced will not suffer from gaping, which is the tendency of fillets to split into fissures. 2.5 CHARACTERISTICS OF FRESH AND SPOILED AQUATIC PRODUCTS  The freshness quality and the extent of spoilage of aquatic products after harvesting and prior to consumption are generally evaluated by using the human senses (sight, smell and touch) 2.6 HANDLING OF FRESH AQUATIC PRODUCTS  Handle aquatic products with care to avoid losses to damage and subsequently to spoilage  Shellfishes should be alive until processing or cooking 2.6.1 Fish  Sort fish according to species and size without delay and keep at low temperatures.  Low temperature, cleanliness, speed and care – important factors in maintaining quality of newly caught fish. 2.6.2 Oysters and Mussels  Harvest with care. Gather in clusters to reduce water loss w/c shortens their life  Byssus gland – secretes sticky hairs w/c must not be pulled out or it will die within hours  Can be chilled 2-4oC using blanket or melting ice. Avoid direct contact w/ ice  Can survive for one week out of water if properly handled  Brush shells first before shucking. Shucked meat must be washed with water 2.6.3 Crabs  Delicate, so don’t handle frequently  Can be kept alive in seawater in lengths of time  Can be kept in moist bags or boxes at high humidity  High temperatures weakens crab 2.6.4 Shrimps  Harvested shrimps must be cleaned and protected at high temperatures  Chilling with crushed ice should be done immediately 2.6.5 Lobsters  Keep alive  14oC – immobilizes lobsters   Beheading dead lobsters prevents blackening. 2.6.6 Squids and cuttlefish  Clean well and store at low temperatures  Crushed ice or ice slurry can be used in chilling. 2.6.7 Seaweeds  Local consumption – washed in clean seawater then packed in baskets with banana leaf covering Chapter 3. CHILLING  Lowering the temperature (chilling, refrigeration and freezing) – key factor in maintaining the quality of fresh fish  Chilling – most common practice; reduction to some point below (-2 to -4oC for super chilling) or above (between 0 – 5oC) the freezing point of water in the fish muscle  Does not stop spoilage but it slows down 3.1 METHODS OF CHILLING 3.1.1 Wet ice (icing)  Most common and useful way of chilling  Cooling – effect of direct contact of ice and fish  Heat transfer from the warm fish to ice resulting to melting of ice and cooling of fish.  Considerations when icing fish:  Sufficient ice be used to maintain 0oC  1:1 – usual ice-fish ratio; more ice be given for longer trips  Arrangement of ice and fish should make drainage of water, blood and slime at ease  Alternate ice and fish. Surround w/ ice on dides, top and bottom  Mixed fish: big on bottom and small on top  Fish w/ delicate skin on top  Gutted: fill w/ ice in belly cavity and arrange w/ belly down in a slanting position inside the container  3.1.2 Chilled Seawater (CSW) or ice slurry  Slush ice or mixture of seawater and crushed ice  Amounts of ice depends on:  Initial temperature of the water and the fish   Size of the container  Quality of insulation  Length of trip  Advantages of CSW over icing:  CSW chills faster than wet ice  Fish do not suffer from physical damage due to crushing or pressure from other fish  Fish in CSW are washed in the slurry  Disadvantage: do not keep longer than wet iced fish 3.1.3 Other methods 3.1.3.4 Refrigerated air  Employed in big commercial boats  Chilled air is circulated by finned evaporator and fan (air blowers)  Fish are packed in containers and stocked in the fish hold  Chilling is slower than icing and CSW.  Cooling time generally exceeds 24 hours  Slow heat transfer 3.1.3.5 Dry ice  Solid carbon dioxide  Cooling is effected by its evaporation  (-78.9oC)  Don’t use in direct contact to avoid cold burns.  Use in air shipment of fish  Restricted use…it expands to gas so it may expel oxygen in airplanes 3.1.3.6 Gel ice mat  Made by freezing a water-based gel  Advantage: bound w/ no chance of water leakage during thawing  Suitable for air transport of fish 3.2 TYPES OF ICE  Ice should be clean 3.2.1 Block ice  Not used directly due to size and weight 3.2.2 Crushed ice  Blocks or slabs crushed mechanically or manually  Irregular size w/ sharp edges – may cause physical damage 3.2.3 Flake ice or “scale”  Freshwater thin flakes  Maintained at -6oC storage  Good ice-fish contact due to large surface area  Disadvantages:  Denser than crushed ice; more ice to use  Tends to clump  Melts very rapidly, less practical for long transport 3.2.4 Tube ice  Last longer and melts more evenly than other shaped ice  Useful for transport in uninsulated containers bulk density midway of flaked ice and crushed ice  Not practical due to cylindrical shape can bruise fish due to relatively large size 3.3 METHODS OF STORING ICED FISH 3.3.1 Bulking  Done in fishing boats to economize space  Disadvantages:  Physical damage due to pressure above and pressure of ice  Poorer quality than shelved or boxed fish (same storage time)  Unloading of catch is difficult 3.3.2 Shelfing  Applicable to large gutted fish  Better or at least equal quality to bulked fish 3.3.3 Boxing  Preferred method  Easily moved for transport  Advantages:  Segregation of first caught to last caught  Small from large  One species from another  Disadvantage:  Greater space occupied than bulking 3.4 TYPES OF CONTAINERS  Points to consider in fish container selection:  Insulating properties  Proper shape and dimensions for the product  Easy to handle, fill and empty  Easy to clean and stack securely one on top of the other   Constructed from nonpoisonous materials  Adequate provision for drainage of melt-water 3.4.1 Plastic box  Made of polymers – chain of monomers.  HDPE and polypropylene – widely used in manufacture of containers 3.4.1.1 Polyethylene (PE)  Low density 0.910 to 0.925 g/cm3  Medium density 0.926 to 0.940 g/cm3  High density  Type III 0.941 to 0.959 g/cm3  Type IV 0.960 g/cm3 & above 3.4.1.2 Polypropylene (PP)  Low density of 0.902 g/cm3  One of lightest plastic  Resistant to grease and most chemicals  Good barrier to water vapor  Can withstand high temperatures  More rigid, stronger and lighter than PE 3.4.1.3 Polystyrene (Styropore)  Low thermal conductivity  Weight saving  Difficult to clean  Do not last long  Do not have drainage for melt-water 3.4.2 Galvanized Iron (GI) Sheet Tubs (Bañera)  Most commonly used container in the Philippines  Easily corrode  Poor insulating property40-50 kg..difficult to handle  Becoming less popular due to polystyrene boxes 3.4.3 Wooden Boxes  Can withstand rough handling  Good insulating property  Not easy to clean  Slightly difficult to handle 3.4.4 Coconut, Bamboo or Rattan boxes  Cheap and easy to handle  Difficult to clean   Do not last long  Ice easily melt  Can kept cool 24 hours if insulated with coconut fiber pillows 3.5 TYPES OF INSULATION  Aim is to slow down rate of heat exchange  Efficiency of insulation is measured w/ thermal conductivity (k)  K = amount of heat in kl calories passing every hour through one sq. m. of material one meter thick when there is a 1oC temperature difference between two surfaces of the material  The lower the k value, the more efficient is the insulation  Choice of insulating material depends on:  Thermal conductivity  Resistance and permeability to water vapor (waterproof)  Density and compressive strength 3.5.1 Cork and fiberglass mat  Good insulation but highly permeable to water vapor 3.5.2 Rice hull, kapok, coconut fibers and sawdust  Cheap but not water resistant  Kapok when compressed loses insulating power 3.5.3 Polystyrene  Low k value  Low density  Low permeability  Low compression resistance 3.5.4 Polyurethane  Same properties with expanded polystyrene  Good vapor resistance 3.6 POINTERS IN HANDLING CHILLED FISH  No form of processing improves quality of spoiled or partially spoiled fish.  Maintain quality by good handling practices from harvest to consumption  Factors to consider in handling chilled fish:  Temperature  Low temperatures (around 0oC) must be maintained until reching consumer  Chill fish ASAP  Keep chilled before processing and at all stages of preparation  Time   Kept all delays at minimum  Know length of time for keeping in the medium  Contamination  Observe good sanitation and hygiene at all times  Damage  Avoid physical damages such as bruises, cuts, punctures, etc. Chapter 4. FREEZING  Keeps fish for several months  Arrests bacterial and enzymatic activity  Dehydration by transformation of water into ice  60-80% of fish is water depending upon species  -5oC – 75% of the water in fish is frozen  -65oC – approx. 12% of water remains unfrozen  3 stages in the freezing process:  Stage 1 – Removal of Heat  Falling of temperature to just below 0oC (FW freezing point)  Freezing rate (FR) is influenced by air temperature (AT)  High FR attained by lowering AT  Stage 2 – Conversion of water to ice (crystallization of water)  Fairly constant -1oC  Around 75% of water freezes (critical zone or period of thermal arrest)  Faster the product pass through this stage the less quality loss will occur  FR is affected by air velocity (AV)  AV – influences removal of latent heat equivalent to 60-70% of heat removed  Stage 3 – Further cooling of frozen fish  Rapid drop of temperature of fish flesh  -30oC is the desired temperature of storage 4.1 TYPES OF FREEZING 4.1.1 Slow freezing  -1 to -5oC – zone of maximum crystal formation  Maximum enzyme activity  Keep this period short  Long freezing can result to bacterial spoilage and protein denaturation 4.1.2 Quick freezing/ Snap freezing   IQF/ individual quick frozen  Usually takes 2 hours or less to go through the zone of maximum crystal formation  Warmest portion of fish should be -20oC. 4.2 FREEZING SYSTEMS  There are 3 basic methods  Choice depend on cost, function and feasibility 4.2.1 Air Blast Freezing  A continuous flow of cold air is passed over the product  Uniform freezing is attained only if the temperature and speed of the air over the product are constant  Air blast freezers can be:  Continuous – where the product moves through a freezer  Batch type – where the product is stationary  Versatile; useful in producing IQF products (crustaceans, fillets, VAP-breaded)  Disadvantage: occupies a lot of space and consume more power than equivalent plate freezers 4.2.2 Contact or plate freezing  Product is placed in direct contact with hollow, metal, freezer plates. Through which a cold fluid is passé  Used for freezing products such as whole fish, fillets, shrimps into blocks.  There are 2 types:  Vertical type – freezing whole fish at sea for bulk freezing  Horizontal plate freezer – requires packing of products into trays or cartons before placing them in the freezer. 4.2.3 Spray or immersion freezing  Product comes in direct contact with the fluid refrigerant  Mainly used for producing very high value and specialized IQF products  Includes liquid nitrogen and carbon dioxide freezers 4.3 FREEZING PROCEDURE Raw material  Freezing at below -10oC will stop bacterial action.  Chemical, biochemical and physical processes leading to irreversible changes will occur at a very slow rate  Hence, the state of the raw material will determine the quality of the final product. Treatment before freezing  Fish must be kept well iced or chilled before freezing   Iced water or chilled seawater (2 parts ice to 1 part water) can be used to lower the temperature of the fish to or close to 0oC.  Dipping or immersion of fish in the slurry for 1-2 hours will be sufficient  Chilling can reduce the time of freezing when slow freezers are used Freezing  Freezing method employed will depend on the type of product to be frozen.  Overloading of the freezer must be avoided  The freezing time must be as short as possible to prevent quality loss Treatment After Freezing  Glazing – dipping or immersion in iced water, 0oC to prevent dehydration and oxidation Packaging  Proper packaging must be used Storage  -30oC – recommended storage temperature 4.4 QUALITY ASSESSMENT OF FROZEN FISH Protein denaturation  Irreversible changes in appearance and texture  Loss in functional properties of the muscle proteins (solubility, water retention, gelling ability) and lipid emulsifying properties and gradual decrease in enzyme activities Lipid changes  Rusting – movement of oil to the surface of the fish during cold storage  Yellow or light brown discoloration  Rancidity – unpleasant odor and color that develop upon oxidation Freezer burn  Excessive drying resulting to matt (white patches on the surface of frozen fish) Dehydration and weight loss  Dehydration (1%) occurs naturally during freezing Development of Cold-Store Flavor and Odor  Due to improper and extended cold storage 4.5 THAWING OF FROZEN PRODUCTS  Quick thawing is important   1) heat is directed into the flesh from the surface  2) heat is generated more or less uniformly throughout the flesh 4.5.1 Thawing in Air Still air  Overnight at room temperature (not >20oC  Single fish (10cm thick) – 8-10 hours to thaw Moving Air (Air blast thawing)  20oC at 8m/s 4.5.2 Thawing in water  Immersion, spraying or combination  Fillets not recommended – may become waterlogged and may lost flavor  Not warmer than 18oC at thawing rate of at least 5mm/s  10 cm thick fish takes 4 ½ hours to thaw 4.5.3 Vacuum thawing  Almost 120 kg of water will condense per ton of fish thawed 4.5.4 Electrical methods  Dielectric (20% of air/vacuum thawing) and electrical resistance heating for thawing or tempering (partial thawing or softening) and microwave heating for tempering only. 4.6 HANDLING OF FROZEN FISH  Do not pry fish apart during thawing  Do not put on floor (cross contamination)  Use clean containers  No repeated freezing and thawing 4.7 MANUFACTURED PRODUCTS 4.7.1 Boneless milkfish  Dorsal = 86-88  Rib bones = 26-28  Lateral = 40-44  Ventral = 44-48  TOTAL = 196-208 4.7.2 Freezing of squids   Peak season = August  Cebu = June-November  Bicol = squid 4.8 TECHNICAL PROBLEMS 4.8.1 Browning or blackening of Tuna and Bonito Meat  Due to oxidation of hemoglobin in blood and myoglobin in muscle  Converted to oxyhemoglobin and oxymyoglobin w/c are brilliant red in color  Further conversion to methahemoglobin and metamyoglobin w/c is dark red or dark brown in color through the action of oxidative enzymes  Adding sodium nitrate or antioxidant (ascorbic acid) prevents discoloration 4.8.2 Green discoloration of tuna meat  Due to TMAO (trimethylamine oxide) in the flesh and other factors such as myoglobin content, cysteine concentration and cooking conditions  To avoid: use fresh tuna for freezing and gutting and bleeding before freezing 4.8.3 Browning or black spot in shrimps and prawns  Melanosis – browning or blackening of frozen shrimps and prawns  Due to oxidation of tyrosine into melanin by the tyrosinase in the blood  Dipping in 1% sodium metabisulphate solution for 30 seconds  3% HQ Bacterol F solution for 15 minutes 4.9 RESEARCH NOTES  Pre-chilling of milkfish in ice at 4Oc right after harvest  FW Tilapia – delaying icing at 4,8 & 12 hours has shelflife of 20, 16 and 24 hours  Cooked shrimps is better than raw prior to freezing Chapter 5. SALTING  One of the earliest techniques for preserving fish.  Preserves by lowering the moisture content to the point where bacterial and enzymatic activities are retarded.  6 to 8% salt content - spoilage organisms generally can’t survive long.  Removes water from the fish by osmosis.  26% - saturated brine solution  30 ppm) and copper (0.5 ppm) – encourages rancidity in fatty fish, unsightly yellowish and brownish color in finished product  Calcium and magnesium sulfates – can impart a desirable whiteness and firmness to the product 5.1.2 Microbiological Quality  Halophiles – results to ‘pinking’ in cured fish  Dun – results from halophilic molds 5.1.3 Physical Properties  Fine grain salt – suitable for brine preparation  Large grain salt – more appropriate in dry salting  Salt burn – resulted from using fine grain salt due to rapid moisture removal in the surface making it hard and prevents entrance of salt to the inside  2/3 coarse grain salt + 1/3 fine grain salt – recom. salt mixture for direct salting 5.2 Factors Influencing Salt Penetration  Fat and protein content. The higher the fat content the slower the salt uptake.  High protein content ( 18-19%) – takes long to attain osmotic equilibrium  Thickness of the flesh - The thicker the flesh, the slower the diffusion of salt  Purity of the salt – the purer the salt, the faster the salt penetration. Impurities such as CaCl and MgCl and sulfates – reduces salt penetration  Temperature during salting – salt uptake faster at higher temperature but the rate of bacterial spoilage is also accelerated.  Freshness of the fish – the fresher the fish, slower the salt penetration 5.3 Methods of salting 5.3.1 Dry salting or Kench process  Rubbing fish with salt before packing and layer sprinkled with salt.  Recommended for lean fish due to oxidation problem in fatty fish.  30% of fish weight – amount of salt to be used  Quantity of salt should not exceed 35-40% 5.3.2 Wet salting  Brining - placing fish in saturated brine (26%)  Pickle-curing – starts as dry salting (1:0.3-0.4/ fish:salt ratio) and liquid or pickle formed were retained. Saturated brine may also be poured. Appropriate for oily fish with fat contents 2% or more. 5.4 Manufactured product   Kench-cured fish (Binoro) – mackerel, sardines, small fish – brined, drained for several hours and then packed in dry salt  Visayan salted/ fermented fish (Tinabal) – maybe classified fermented but fish retains natural shape (from Leyte) parrot fish and frigate tuna.  Shrimp cake (Guinamos) - 2:3 salt to shrimp then tracing/pounding is done  Salted sea urchin – Tripneustes gratilla. Gonads ranges from orange to yellow and from greenish yellow to brown. Bright orange gonads – preferred in Japanese market. 5.5 Spoilage of Salted Fish  ‘Pink’ or Reddening – halophilic bacteria w/c has a pink or rose color -Pseudomonas salinaria and Sarcina littoralis  Dun – peppering of light brown spots or fawn spots. Caused by molds of Wallema genus grows at 5-26% salt concentration, 10-37˚C (opt. 25˚C) and pH 4-8 (opt. 6-7). Prevention: good sanitation, good ventilation and drying or dipping in 0.1% sorbic acid.  Sliming – semi-greasy, sticky, glistening layer of yellow-gray or beige color. Sour pungent off-odor. Caused by slime producing bacteria can live (6-12% salt).  Souring – due to improper salting and results to uneven salt distribution  Salt burn – due to excessive amount of fine salt that draws moisture rapidly  ‘Putty’ fish – related to sliming, occurs in thickest part of fish where the rate of increase in salt concentration is slowest. Chapter 6. DRYING  Drying – refers to removal of water from the product, exposure to currents of air and humidity  Dehydration – controlled and artificial means like mechanical dryers 