Download - Fish spoilage
FISH SPOILAGE AND METHOD OF DETECTION
Dr. Babasaheb KumbharM.V.Sc scholarCollege of Veterinary Sciences,
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
FISH SPOILAGE
FISH POSINIGN
In addition, the following factors contribute to spoilage of fish.High fat contentHigh protein contentWeak muscle tissueExtent of bacterial contaminationAmbient temperatureHigh moisture contentUnhygienic handlingRigor mortis hastened-- struggling of fish, lack of oxygen, warm temp. Use of an antibiotic, ice or dip
RANCID ODOR
The process involves three stages:
1. Rigor mortis2. Autolysis3. Bacterial invasion and putrefaction
Spoilage is a result of 3 separate processes
These are:– Enzymatic Spoilage– Mechanical damage – Bacterial Action– Chemical Decomposition--Oxidation
ENZYMATIC SPOILAGE Autolysis
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. Cathepsin2. Calpain3. Trypsin4. Chymotryps
in
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
MECHANICAL SPOILAGE
CARELESS HANDLING CAN RESULT IN:
•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.
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.
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
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
The guts contain huge numbers of bacteria which can easily contaminate the flesh inside the belly cavity. If acids then break down the wall of the cavity they penetrate to all other parts of the flesh. This process is called “Autodigestion”
Proteins Proteolytic micro-organisms Amino acids + Amines + NH3 +
H2S
Carbohydrates Fermentive micro-organisms Acid + Alcohols + Gases
Fats Lipolytic micro-organisms
Fatty acids + Glycerol
BACTERIA CAUSING SPOILAGE
At chilling temperature – Pseudomonas, Achromobacter, Flavobacterium
At ordinary atmospheric temp.- Escherichia, Proteus, Serratia, Sarcina & Clostridium
At higher temperature- Micrococcus & Bacillus
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
The important changes brought out by the action of the bacteria in fish are as follows.
iii) Breakdown in UreaThe high concentration of urea degraded to ammonia by
the microorganisms--- offensive odour.
i) Reduction of TMAO to TMAMarine 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.
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
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
Sam
ple
pre
para
tion 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
Assessment of fish spoilagePhysical 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.
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
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, indicates
pH range).
Evaluation of putrefaction/ decomposition :
denote the end product of the spoilage (indicator) and do not give any idea about the degree of spoilage.
Chemical indicators of spoilage (late)
Chemical tests1 Trimethylamine (TMA)2 Total volatile basic nitrogen (TVBN)3 Volatile reducing substance (VRS)4 Indole5 Skatole 6 Hydrogen sulphide
iv. Evaluation of spoilage based on lipid markers:
Lipid as indicator of spoilage
Parameter
1 Peroxide index
2 Thiobarbitanic acid test (TBA)
3 Rancidity
4 Texture
5 Refractive index
6 Electrical conductivity
LIMITING SPOILAGE There are three main substances which, if
reduced, would limit the spoilage processes They are:
Water content; Enzymes; Fat content.
1. if the water content reduced:– The chemical decomposition- reduce– The bacteria present would be deprived
of one of the substances needed for their survival.
LIMITING SPOILAGE2. Reduction in the concentration of enzymes
reduce chemical decomposition.
3. If the fat content of the fish is reduced, there is less possibility of oxidation occurring. This means that there is less chance of the taste of the fish being spoilt due to rancidity of the fat.
Handling and Storage– Careful handling of the fish means that, at all stages,
it is important to prevent damage to the fish.– Careless handling can result in damage
THANK YOU
