Microbial spoilage of Fish & sea products
- 1. D R . Z A N W A R S . R . D E P T O F F I M , M G M C F T , G A N D H E L I . Contamination, Preservation & Spoilage of Fish & Sea products
- 3. Contamination Microbial flora of living fish depends on the water in which they live. Slime on the outer surface of fish contain Pseudomonas, Acinetobacter, Moraxella, Alcaligenes, Micrococcus, Flavobacterium, Corynebacterium, Sarcina, Serratia, Vibrio and Bacillus. Bacteria on fish from northern waters are mostly psychrophilies, where as fish from tropical water plus species of Aeromonas, Lactobacillus, Brevibacterium, Alcaligenes and Streptococcus. Intestines of fish from both sources are found bacteria of the genera Alcaligenes, Pseudomonas, Flavobacterium, Vibrio and Bacillus, Clostridium and Escherichia.
- 4. Boats, boxes, bins, fish houses and fishers soon become heavily contaminated with these bacteria. Oyster and other shell fish contain Alcaligenes, Flavobacterium, Moraxella, Acinetobacter. These fish thrush water bodies and pick up soil and micro organisms. Number of micro organisms on the skin of fish can be influenced by the method of catching. Trawling fish nets along the bottom for long periods results in exposure of the fish to high bacterial cants in the sediment. Fish cakes and fish sticks may have contamination from potatoes, spices and flavorings etc.
- 6. Preservation Use of heat Use of low temperatures (chilling & freezing) Irradiation Drying Use of preservatives Antioxidants Preservatives incorporated in ices
- 8. 1. The kind of fish Flat fish spoil more readily than round fish because they pass through rigor mortis more rapidly. But flat fish like halibut keeps longer because of the low PH (5.5) of its flesh. Certain fatty fish deteriorate rapidly because of the oxidation of the unsaturated of their oils. Fishes high in triethylamine oxide soon yield appreciable amounts of the “stale-fishy” trimethylamine.
- 9. 2. Condition of the fish when caught Fish that are exhausted as the result of struggling, lack of oxygen and excessive handling spoil more rapidly than those brought in with less ado, probably because of the exhaustion of glycogen and hence smaller drop in pH of the flesh. “Feedy fish” i.e., those full of food when caught, are more perishable than those with an empty intestinal tract.
- 10. 3. The kind and extent of contamination of the fish flesh with bacteria Contamination occurs from mud, water, handlers, exterior slime and intestinal content of the fish. They are supposed to enter the gills of the fish, from which they pass through the vascular system and thus invade the flesh. Contamination takes place in the net, fishing boat on the docks etc.
- 11. 4. Temperature Chilling the fish is the most commonly used method for preventing or delaying bacteria growth and hence spoilage until the fish is used or otherwise processed. Cooling should be rapid as possible 0 to -1°C and this low temperature should be maintained. Obviously the warmer the temperature, the shorter the storage life of the fish still more effective in its preservation. 5. Use of an antibiotic ice or dip
- 12. Evidences of spoilage The change is gradual from a fresh condition to staleness and then to inedibility it is difficult to determine or agree on the first appearance of spoilage. Practical tests to determine the quality of fish has been sought for many years, but none has proved entirely satisfactory. Trimethylamine test used on salt water fish. Estimate of volatile acids or volatile bases or a test for pH, H2S, ammonia etc. are used Bacteriological tests are too slow to be useful.
- 13. :The process involves three stages 1. Rigor mortis 2. Autolysis 3. Bacterial invasion and putrefaction Spoilage is a result of 3 separate processes These are: – Enzymatic Spoilage – Mechanical damage – Bacterial Action – Chemical Decomposition-Oxidation
- 14. BACTERIA CAUSING SPOILAGE At chilling temperature – Pseudomonas, Achromobacter, Flavobacterium At ordinary atmospheric temp.- Escherichia, Proteus, Serratia, Sarcina & Clostridium At higher temperature- Micrococcus & Bacillus
- 15. Discolorations of fish Yellow to greenish- Pseudomonas fluorescence, micrococcus & others Red or pink- Sarcina, Micrococcus, or Bacillus species, or by molds & yeasts Chocolate-brown- Asporogenous yeast
- 17. Spoilage of special Kind of fishes & seafoods Salt Fish- Halophilic bacteria (Serratia, Micrococcus, Bacillus, Alcaligenes, Pseudomonas and others). These bacteria cause discolorations, a red color being common. Molds are the chief spoilage organisms on smoked fish. Marinated (sour picked) fish should present no spoilage problems unless the acid content is low enough to permit growth of lactic acid bacteria or the entrance of air permits mold growth.
- 18. In chilled shrimps - Acinetobacter, Moraxella and Vibrio. Crabmeat - Pseudomonas, Acinetobacter, Proteus. Raw lobsters - Pseudomonas, Alcaligenes and Flavobacterium. Crabs and oysters may contain sps of Vibrio including Vibrio parahaemolyticus. At temperatures near freezing Pseudomonas, Acinetobacter and Moraxella species are the most important spoilage bacteria but Flavobacterium and Micrococcus sps also may grow. The spoilage is termed “souring” although the changes are chiefly proteolytic. At higher temperatures the souring may be the result of the fermentation of the sugars by coliform bacteria, Streptococci, Lactobacilli and yeast to produce acids and a sour odor. Early growth of Serratia, Pseudomonas, Proteus and Clostridium may takes place. An uncommon type of spoilage by asporogenous yeast causes pink oysters.