TECHNOLOGY OF FISHERY PRODUCTS

FISH HANDLING AND SPOILAGE The differences in appearance of fresh and stale or spoiling fish may be summarised as follows : Fresh Skin and colours bright Scales adhere atrongly Eyes clear, not sunken or wrinkled Flesh firm, elastic, finger impressions do not remain Smell : fresh at exterior and gill Little slime on skin Body rigid or still Fish skins in water Stale or Spoiling Colours plate and bleach Scales loose Eyes cloudy, wrinkled, sunken Flesh flabby and soft, finger impressions remain Smell : state or sour, especially gills Skin slimy Body flabby and limp Fish floats if very bad

FISH PRESERVATION METHODS Temperature methods such as heat in canning and low temperatures in chillin and freezing Chemical methods involving the use of salt and vinegar Drying, either natural or artificial The methods used for fish preservation aim at control of spoilage and use three general techniques :

CANNING Adequate heat processes to render the fish in a can commercially sterile in the same way as for any other product are carried out The fish may be canned in oil, in sauces, in brine or on its own and of course is stable and unspoiled over indefinite periods

CHILLING Marine bacteria which are found on fish grow over a wide range of temperatures. Thus while their optimum growth temperatures may be about 20ºC, some can grow at temperatures as low as -10ºC Chilling, utilising temperatures in ice of app. 0ºC can therefore only delay spoilage and fish packed in ice will remain fresh for no longer than 12 to 14 days even under the best handling conditions.

FREEZING Freezing process involve the storage of fish at temperatures well below 0ºC. In order to inhibit bacterial growth over long periods temperatures of -10ºC to -12ºC are necessary, however, other undesirable changes such as protein denaturation and fat rancidity can be overcome only by the use of temperatures as low as -20ºC to -30ºC

SALTING Salting is an ancient form of preservation still much in use today. Methods of salting vary greatly from country to country but in general two methods are employed : dry salting and wet or pickle curing

a. Dry Salting In which salt is interspered between layers of gutted and cleaned fish. The proportions of salt vary from 10% to 35% The salt withdraws moistures as it penetrates the flesh and denaturates the protein The flesh becomes opaque and loses its stickiness becoming “struck through” The process takes days, salt content of the flesh rises to about 20% and the fish has lost about 30% of its original weight. This “green cure” is then dried hard either hard either artificially or in the open

b. Wet or Pickle Curing In which gutted and cleaned fishn are packed in barrels of a pickle of salt and fish juices The process is complete in about 20 days Both types oif salted fish can remain in good condition for 2-3 months at temperatures below 10ºC Salted fish owe their stability to three factors : a.The direct action of sodium chloride on putrefactive types of organisms b.The removal of oxygen from the tissues preventing microbial growth c.The interference of sodium chloride with the action of proteolytic enzymes in the flesh

SMOKING 4 basic processes Brining or salting Drying Treatment with smoke Treatment with heat

SMOKING The smoking process cause a decrease in moisture content, an increase in salt content and a deposit of smoke constituents on the surface of the fish. Also a pellicle or superficial layer of denaturated protein forms on the outer portion of the fish. The storage life of the fish after smoking will vary depending on the extent to which each of the 4 basic processes is carried out The drying and salting act to preserve the fish by lowering water activity and as described under salting

DRYING Fish drying carried out under ambient conditions and fish dehydration carried out artificially enhance the storage life of fish by decreasing its water content In a drying process moisture content is reduced from about 80% to about 10% and may take several months In cold climates, dried fish may last for several years with control of spoilage being due to control of microbial growth and enzyme activity by the low moisture content

Fermented Fish Products A number of fermented fish products are prepared in many regions of the world In general the fish is mixed with a certain amount of salt and allowed to ferment

FISH MEAL PRODUCTION Fish meal is produced from a number of raw materials which include : skeletal remains of filleted fish, fish cannery waste, fish offal, whole fish generally regarded as inedible, some varieties of herring, pilchards and many very small fish The fish is then carried by a screw conveyer into a steam heated continuous cooker where it spends about 10 minutes After cooking the mass is put through a continuous screw press The fluid removed is known as ‘stickwater’

FISH MEAL PRODUCTION... (2) In this particular plant, the stickwater is put through a screen and any solids added to the press cake Fish oil may then be separated from the stickwater by centrifugation, and is refined by steam treatment and stored for sale

FISH MEAL PRODUCTION...(3)

FISH MEAL PRODUCTION... (4) The composition of the meal produced in this plant is : Minimum protein : 70%Fat : 6-11%Maximum fibre : 10%Maximum salt : 4%Moisture : approx. 5%Ethoxyquin (antioxidant) : 400 ppm

USES OF FISH MEAL Fish meal is of particularly value because of its high content of essential amino acid, especially lysine This makes fish meal of special value in combination with cereal feeds which are notoriously low in lysine content In addition fish meal provides vitamins and minerals not provided by cereal grains or plant protein supplements

FISH PROTEIN CONCENTRATE (FPC) Fish Protein Concentrate or fish flour, is as accepted as human food and not animal food FPC meets the desired requirements whereas, with the possible exception of non-fat milk powder, no other dry animal protein in commercial use can Since any of the thousands of fish species under the seas which cover 70% of world’s surface could be used as a source of protein supplement

FPC MANUFACTURE The steps involved are : a. Fish ground into small piecesb. Suspended in EtCl2 (Ethylene dichloride)c. Put into cooker, heated by indirect steam d. Constant boiling mixture of H2O/EtCl2 forms and is distilled off (boiling point 71ºC) e. During this distillation, H2O is removed continuously as is dehydrated, defatted meal f. Meal is desolventised g. Deodorisation carried out by methanol extraction (removes amines and associated compounds) h. Oil separated from solvent by destillation