Bacterial spoilage is the most important cause of fish spoilage
- 2. A series of complicated metabolic process Enzymes and bacteria Undesirable or unacceptable Changes in sensory characteristics. SPOILAGE CONCEPT Fish is one of the most perishable food items FRESH FISH???? SPOILED FISH???? Food spoilage is considered as any change that renders the product unacceptable for human consumption
- 3. Fish Die Rigor Mortis Autolysis Microbial Activity Spoilage Sequence of events during spoilage
- 4. RIGOR MORTIS Progressive stiffening of muscle shortly after death Starts from the tail towards the head Duration depends on Species of fish Size Catching method Handling of fish Temperature Physical condition of the fish
- 5. Why does a fish spoil? Blood circulation stops Oxygen supply fails Energy production stops Respiration ceases Acid forms in muscles Muscle stiffing Muscle softing Tissue breakdown Bacterial growth Aerial oxidation FISH Fig: Factors and causes of fish spoilage
- 6. Fish spoils for three reasons/modes of spoilage Action of enzymes/Autolytic enzymatic spoilage Action of bacteria/Bacterial spoilage Oxidation of lipid/Oxidative spoilage Bacterial spoilage is the most important cause of fish spoilage
- 7. Autolytic spoilage (Enzymatic) Major changes/events during enzymatic/autolytic spoilage Rigor mortis Glycolysis Autolytic enzyme action and flavor changes (Necleotide degradation) Belly bursting Color changes
- 8. The autolytic changes that occur in chilled/frozen fish (FAO, 2005) Autolytic spoilage (Enzymatic)
- 9. The subsurface flesh of live healthy fish is usually sterile and does not contain any bacteria or other organisms. But, microorganisms colonize the skin, gills and the gastrointestinal tract of fish. The geographical location, the season and the method of harvest are the reasons deciding the number and diversity of microbes. The natural fish microflora tends to reflect the microbial communities of the surrounding waters. Fish harvested from eutrophic and warm waters will present higher bacterial numbers than fish from clean and cold waters. Gram-negative genera including: Acinetobacter, Flavobacterium, Moraxella, Shwenella and Pseudomonas dominates the autochthonous bacteria flora of fish. Vibrio, Photobacterium and Aeromonas spp. are also common aquatic bacteria, and typical of fish flora. Gram-positive organisms such as Bacillus, Micrococcus, Clostridium, Lactobacillus and coryneforms can also be found in varying proportions on fish. Pseudomonas, Flavobacteria, Acinetobacter, Aeromonas and Moroxella are important Spoilage organisms. Microbial spoilage
- 10. Major deteriorative changes brought about by microorganisms/bacteria Formation of ammonia Formation of TMA Histamine formation Indole production Other volatile sulphur compounds Microbial spoilage
- 11. Substrate Product by bacterial activity Odor Inosine Hypoxanthine Characteristics odor Methionine and Cystine H2S Methyl mercapton, Characteristics odor, Cabbage like or strong sulphide, Carbohydrate and lactate Acetic acid, CO2+H2O Glycine, Sesine, Leusine Acetic , Butyric & Propionic acid Fruity TMAO TMA Fishy or Ammonical Urea/amino acid NH3 Fishy or ammonical Substrate and off-odour/off-flavour compounds produced by bacteria during spoilage of fish Microbial spoilage
- 12. lists spoilage bacteria in descending order of spoilage activity. The compounds formed during spoilage through microbial metabolism Microbial spoilage
- 13. Involved in fish spoilage at normal temperature: 1. Escherichia coli 2. Proteus 3. Serratia 4. Sarcina 5. Clostridium Spoilage of special kinds of fish and sea foods: Salt fish spoiled by : Serratia, Micrococcus, Bacillus, Pseudomonas. Smoked fish : Molds Marinated (Sour pickled) fish : Lactic acid bacteria. Canned fish : Clostridium botulinum, . Chilled Shrimp : Achromobacter , Pseudomonas. Raw lobsters : Pseudomonas, Bacillus. Oyesters : Asparegenous yeast.
- 14. Oxidative spoilage Lipid oxidation is a major cause of deterioration and spoilage for the pelagic fish species such as mackerel and herring with high oil/fat content stored fat in their flesh Lipid oxidation involves a three stage free radical mechanism: initiation, propagation and termination In fish, lipid oxidation can occur enzymatically or non-enzymatically. The enzymatic hydrolysis of fats by lipases is termed lipolysis (fat deterioration). During this process, lipases split the glycerides forming free fatty acids which are responsible for: (a) common offflavour, frequently referred to as rancidity and (b) reducing the oil quality The enzymes involved are the lipases present in the skin, blood and tissue. The main enzymes in fish lipid hydrolysis are triacyl lipase, phospholipase A2 and phospholipase
- 16. CHANGES IN EATING QUALITY OF FISH IN ICE Phase 1 The fish is very fresh and has a sweet, seaweedy and delicate taste. The taste can be very slightly metallic. Phase 2 There is a loss of the characteristic odour and taste. The flesh becomes neutral but has no off-flavours. The texture is still pleasant Phase 3 There is sign of spoilage and a range of volatile, unpleasant-smelling substances is produced depending on the fish species and type of spoilage (aerobic, anaerobic). One of the volatile compounds may be trimethylamine (TMA) derived from the bacterial reduction of trimethyl-aminoxide (TMAO). TMA has a very characteristic "fishy" smell. At the beginning of the phase the off-flavour may be slightly sour, fruity and slightly bitter, especially in fatty fish. During the later stages sickly sweet, cabbage-like, ammoniacal, sulphurous and rancid smells develop. The texture becomes either soft and watery or tough and dry. Phase 4 The fish can be characterized as spoiled and putrid
- 17. Evidence of Fish spoilage Factors influencing kind and rate of spoilage How does fish spoilage accelerate? How can we delay or stop fish spoilage
- 18. Evidence of Fish spoilage: Eyes dull and sunken Gills no longer red, but pale pink, brownish or grey and putrid smell. Anus wet, swollen and red Surface of fish dull, covered with opaque slime, sour or putrid smell. Flesh very soft and flabby. Abnormally grey or reddish in color, moldy, sour or putrid smell.
- 19. Factors influencing kind and rate of spoilage: 1. The kind of fish: 2. The condition of the fish when caught 3. Kind and extent of contamination 4. Temperature
- 20. Factors influencing kind and rate of spoilage: 1. The kind of fish: Flat fish spoil more rapidly than round fish because they pass through rigor mortis more rapidly. Certain fatty fish deteriorate rapidly because of oxidation of the unsaturated fats of their oils. Fishes in high TMAO soon produce appreciable amount of the fish flavor of TMA. 2. The condition of the fish when caught: Fish that are exhausted as a result of struggling , lack of O2 and excessive handling spoil more rapidly because of the exhaustion of glycogen, hence smaller drop pH . Feedy fish those full of food when caught, are more perishable than those with an empty intestinal tract.
- 21. 3. Kind and extent of contamination Come from mudwater, handlers, and the exterior slime and intestinal content of the fish and The greater the load of bacteria on the fish, the more rapid the spoilage. 4. Temperature: Chilling the fish is the most commonly used method for preventing spoilage. Cooling should be as rapid as possible to 00-10 C. The warmer the temperature, the shorter the storage life of the fish. Prompt and rapid freezing of the fish is more effective in preservation. Factors influencing kind and rate of spoilage:
- 22. How does fish spoilage accelerate? Spoilage of fish is accelerated by- Struggle/excitation during fishing Rough handling, injury or damage of muscle Improper sanitation Contamination Delay of icing Exposed to sun at any stage Delay of icing is the most important critical factor that accelerates the spoilage
- 23. How can we delay or stop fish spoilage Fish spoilage can be delayed or stopped by Protecting fish from physical injury or muscle destruction Applying proper sanitation and avoiding contamination Lowering temperature immediately: keeping cool during transportation and storage Destroying enzyme and killing bacteria by high temperature: canning, heat processing Reducing water content in fish body: drying, salting, smoking