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Jamaica Health Tips Blog

January 2014

Things to look out for when buying fish

 Fish, when freshly caught, is relatively wholesome.  The quality of the fish starts to deteriorate as soon as it is taken  from the water.  The principal cause of fish condemnation is decay.  Factors influencing the rapid spoilage of fish are: 
  1. Microbial – several species of microbes are always present in the surface slime and intestinal tract of the healthy fish.  As long as the fish remains alive, these are held in check and the flesh of the healthy fish remains sterile.  However, as soon as the fish dies, these reproduce rapidly and attack all the constituents of the tissues.  Since these organisms live on the cold-blooded vertebrate at low ocean temperatures, they are able to resist ordinary refrigeration temperatures.  If microbial decomposition must be retarded, fish, upon being caught, should be immediately stored at temperatures below 0ºC.
  2. Physiological – due to the fight and consequent exertion when caught, glycogen in the muscles is depleted or nearly so.  There is therefore little glycogen to convert into lactic acid in slowing bacterial growth in muscles is limited.
  3. Chemical – besides bacteria, enzymes act upon certain constituents of the fish, breaking it down into simpler substances.  This is called self-digestion or autolysis. The growth and activities of certain bacteria on the surface of the fish produces undesirable chemical substances called trimethylamine which is responsible for the fishy odor of spoilt fish.  This chemical then diffuses into the flesh of the fish causing spoilage.
 
Characteristics of Good Wet Fish
  1. Clear, bright, slightly protruding eyes with black pupils.
  2. Gills are bright red in color, odorless and usually closed.
  3. Moderate amount of natural slime covering fish, skin shiny and color unfaded, scales are strongly adherent, creamy white or transparent slime.
  4. Flesh is firm to the touch, solid, opaque, elastic and strongly attached to backbone.
  5. Abdomen clean and free from offensive odor.  Belly walls are firm with no discoloration.
  6. Blood along the backbone in the visceral cavity is bright red.
  7. Pleasant odor (briny)
  8. Body stiff and tail rigid.
  9. The carcass will sink in water.
 Characteristics of Stale Wet Fish
  1. Dull, sunken grey eyes which will disappear in extremely rotten fish.
  2. Gills are of very pale pink or dark brown color, slimy and have foul odor.
  3. Natural slime is yellowish and has a bad odor, dull appearance, many missing scales as they are easily detached from the skin.
  4. Flesh is soft and limp, transparent and pits easily on pressure and can be easily loosened from backbone.
  5. Abdomen discolored with offensive odor, belly wall soft and discolored.
  6. Blood along backbone is dark to black in color, with foul odor.
  7. Strong rank odor, progressing into a putrid, rotten fish odor.
  8. Body limp and pliable.
  9. The carcass will float in water.
 
Care of Fresh Fish
     1. Minimum handling – the less handling fish receives, the longer it will remain wholesome and the less likelihood of it causing fish            poisoning.
     2. Fresh fish should be buried in ice that is relatively finely ground or shaven.
     3. It is poor practice to allow fish fillet, sliced fish or fish with flesh exposed to come in direct contact with water or ice as this will          spoil the flavour and appearance and result in a soggy unpalatable product.
     4. Refrigeration is necessary at all times to keep down bacterial action and autolysis.
 
 Smoked Fish (Herring)
  Good Fish
     1. Flesh should be firm, dry and free from stains
     2. Flesh should have fresh, clean, smoky odor
  Bad Fish
     1. Flesh is sweaty, soft and slimy.
     2. Flesh is moldy and has bad odor.

  Dried Saltfish 
 Good Fish
     1. Flesh should be firm, clear in colour, fairly dry on surface, neatly trimmed.
     2. Always stored in dry cool place.
     3. Free of insect pests and dirt.
 Bad Fish
  1. Flesh is discolored, (pink fungus growth).
  2. Wet and moist saltfish not properly stored.
  3. May be infested with Lasioderma or other pests.

 Pickled Fish  
  Good Fish 
      1. Fish should be covered with clean liquor.
      2.Odor should be pleasant, pickle odor. 
      3. Fish should be firm and free from bloodstained and broken pieces. 
 Bad Fish
  1. Fish only partially covered or covered with muddy liquor.
  2. Foul or rancid odor
  3. Fish is bloodstained, discolored and broken into pieces.

 Sound Oysters
 The outside should be clean and free from dirt, with shells tightly closed. 
  When a handful is rubbed together, they will sound like pebbles.   
  They will sink in water and has a pleasant odor.      
  If the pH of the liquor is tested, it will be between 6 and 7. ·      
  The liquor appears milky especially during the spawning season (spring).  
 Stale/Unsound Oysters    
 Shell not closed.    
 When shaken, does not have a pebble like sound.   
 Unpleasant odor, excessive dirt and slime.    
 PH of the liquor more acidic and has an opaque appearance.    
 has a black or dark ring in the inside of the shell ·     
 Floats in water.   

 Oysters removed from shell should be stored in sterile containers and if being kept for over 4 days, should be stored  at 30ºF or  below.
 
 Source: Marcia Reid (lecturer at University of Technology, Jamaica.  Lecture notes.)
 
  Are you buying safe fish? leave a comment below.