Fish Chapter 3 PDF

FISH 1  Learning Objectives Able to describe the various classification and composition of fish Able to differentiate between fish muscle & beef muscle Able to explain the post mortem changes in fish and factors causing spoilage of fish...

FISH 1  Learning Objectives Able to describe the various classification and composition of fish Able to differentiate between fish muscle & beef muscle Able to explain the post mortem changes in fish and factors causing spoilage of fish 2  Classification White fish: eg cod, haddock, plaice, sole, ray, turbot, ‘gelama’( croaker), ‘ikan merah’ (red snappers), sting ray Oily fish: eg trout, herring, mackerel, sardines, salmon, ‘terubuk’ Shell fish: eg lobster, crab, shrimp, oyster, mussels 3  Composition Nutrient White fish Oily fish Shell fish (%) Protein 17.5 18.6 20 Fat 0.5 10.9 0.5 CHO 0 0 2 Minerals 1.2 2.6 3.5 Vitamins B1, B2 A,D,B B1, B2 Water 80 67.5 74 4 Proteins 16-22% - sarcoplasmic proteins (myoalbumin, globulin and enzymes) 75% - myofibrillar proteins (actin, myosin, tropomyosin and actomyosin) Red muscle Reddish muscle found underneath skin of many fish near the lateral line – heavily pigmented & acts a storehouse for fat, glycogen and other metabolites Lipids Phospholipids & TAGs Up to 40 percent of long-chain fatty acids are highly unsaturated (18:3, DHA* & EPA**), thus having positive health implications, but present a technical challenge in dealing with the rapid development of rancidity. * DHA = Docosa– 4,7,10,13,16,19 hexaenoic acid 5 **EPA = Eicosa–5,8,11,14,17 pentaenoic acid  Difference between fish muscle & beef muscle Fibres of fish muscle (called myotomes) are short (up to abt 3 cm in length) & their ends are inserted into sheets of connective tissue called myocommata Fish muscle contains a small amount of connective tissue During cooking the collagen of the connective tissue sheets of fish are hydrolysed to gelatine and the muscle segments/ myotomes are freed & separates as flakes Also, the collagen of fish connective tissue is degraded at a lower temp than that of mammalian C.T. 6 FISH MUSCLE 7 Post Mortem Changes in Fish After death, rigor mortis occurs, as in mammals, but of shorter duration (1-7 hrs after death) A drop in pH also occurs due to lactic acid formation, accompanying rigor mortis formation pH just > 7.0 6.2 - 6.5 (ultimate pH) Chalkiness: condition of fish in which the fish muscle appears dull, white, opaque, soft & flabby (similar to PSE meat). In this condition, ultimate pH of fish muscle = 6.0 or