fish spoilage and list of various test for assesment of fish spoilage
1. FISH SPOILAGE AND METHOD OF DETECTION Dr. Babasaheb Kumbhar M.V.Sc scholar College of Veterinary Sciences, Hyderabad firstname.lastname@example.org
2. The most important things to look for the freshness of fish are: The general appearance eyes, gills, surface slime and scales and the firmness or softness of the flesh. The appearance, particularly the presence and absence of discoloration along the underside, of the backbone. The appearance of the belly walls. The odor of the gills and belly cavity Presence or Absence of rigor mortis or death stiffening
3. FISH SPOILAGE FISH POSINIGN In addition, the following factors contribute to spoilage of fish. High fat content High protein content Weak muscle tissue Extent of bacterial contamination Ambient temperature High moisture content Unhygienic handling Rigor mortis hastened-- struggling of fish, lack of oxygen, warm temp. Use of an antibiotic, ice or dip RANCID ODOR
4. 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
5. ENZYMATIC SPOILAGE Careless handling of fish Fish cell broken Release of autolytic enzymes Production of spoilage substances These substance create the very good environment Favours growth of micro organisms Spoilage substances are 1. Cathepsin 2. Calpain 3. Trypsin 4. Chymotrypsin
6. Protenase Digest muscle protein of fish Result into production AA & nitrogenous compounds Further decomposition produce Production of NH3 + CO2 + volatile basic compound like Amines and Fatty acids Production of Indole, skatole etc Foul smell of fish
7. MECHANICAL SPOILAGE Bruised flesh The darkening is caused by burst blood vessels. Broken skin bacteria to enter the flesh Burst guts bacteria and enzymes to contaminate the flesh.
8. Factor responsible for microbial spoilage These are: Suitable temperatures (Bacteria grow much faster in the warmth); The presence of water; Suitable chemical substances present in the flesh as a source of food.
9. BACTRIOLOGICAL SPOILAGE Millions of bacterial present on outer surface and inside the fish Healthy fish natural protection against the harmful bacteria Live fish bacteria present on skin & gills, intestine but can not attack the fish muscle
10. Died fish bacteria penetrate the fish muscle more rapid for thin skin fish Bacteria & enzymes changes fish odour, flavour to sour, gassy, fruity & finally ammonia &faecal odour Multiply quickly and produce its metabolites that are responsible for the causes of spoilage When fish died some of the bacteria enters in the flesh
12. BACTERIA CAUSING SPOILAGE At chilling temperature Pseudomonas, Achromobacter, Flavobacterium At ordinary atmospheric temp.- Escherichia, Proteus, Serratia, Sarcina & Clostridium At higher temperature- Micrococcus & Bacillus
13. 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
14. iii) Breakdown in Urea The high concentration of urea degraded to ammonia by the microorganisms--- offensive odour. i) Reduction of TMAO to TMA Marine fish contains a small percentage of odorless TMAO which is reduced to an offensive smelling TMA by the action of bacteria. ii) Breakdown of Amino Acids & formation of Primary Amines The bacterial action of amino acids present in the fish muscle leads to formation of primary amines. e.g. Formation of Histamine from Histidine, Arginine from Glutamic acid etc. This bacterial action may cause food poisoning in extreme cases.
15. CHEMICAL SPOILAGE The chemicals present in living things are able to change due to them either splitting up or joining together. In both cases new chemicals are formed. It is more pronounced in fat fishes e.g. oil sardine, mackerels, catla, trout, grass carp etc. Depends upon Temperature:- high temperature rapid spoilage Water availability Enzymes
16. Fat oxidation occurs after autolysis & bacterial spoilage High Lipid concentration contribute spoilage Fat mainly unsaturated fatty acid easily oxidised by atm.O2 Increase temperature & exposure to light increase oxidation rate bad & unpleasant odour & rancid taste. (sour or stale smell or taste ) Rancidity e.g. Herring & Mackerel
17. Samplepreparation For proximate/BACTERIOLOGICAL analysis of fish first place in plastic bags Cold chain by in ice Thaw by immersion in a agitated water bath approx. at 20 C Judge the completion of thawing by gently squeezing the bag until no hard core or ice crystal can be left Render the thawed or wet fish into uniform mass either by double mincing or used of an electrical driven rotary chopper store the sample in a air tight container. Analyse as quickly as possible If storage is necessary keep at a temperature not exceeding 4C For estimation of amines and total volatile bases for frozen fish, thaw at a temp not exceeding 4C, mince or chop in rotary homogenizer Ensure that the product remains at or about 4C by pre-cooling the equipment. Mix the sample and analyze immediately
18. Assessment of fish spoilage Physical method- instrumental test piercing a Torrymeter on the skin of about 16 randomly selected fish and picking 1 of the result as representing the entire lot. Subjective method- involves the use of human sense organs and not machines, chemicals or reagents. called Sensory tests, may be biased but its represent the customers view Organoleptic test utilizing the sense of touch, smell, sight and taste for quality assessment of fish. Sight- gill colour, presence/absence of indentation Flavour- for degree of freshness Texture- state of the muscles firmly held condition of the belly, or soft presence of blemishes and parasites on fish. Visual exam in cured fish general appearance, degree of insect/ mould infestation intensity of smoking from appearance bulging cans, broken fishes.
19. Touch- texture of fish, elastic firm, soft or flabby, fragmentation in dried whole fish if fish end without breaking it is flexible Smell Good and bad flavour, smoke or cooked. Taste Sweet, bitter, salt and sour,(salty or acidic) fermented and marinades Flavour a combination of taste and odour cause by volatile organic compounds. Mostly use objective test rather than taste panel evaluation eventhough too expensive (chromatograph which measure a flavour at a time). Thus they often train taste panel to prevent
20. Physicochemical: Determination of pH: Method of pH determination : A. Using digital pH meter B. Indicator pH strips (just give an indication of pH but not accurate), C. Litmus test (gives an idea of range but not actual pH) D. Chemical indicator method (Nitrazine yellow