Types of white fish
whiting, john dory, flathead
<5% fat
delicate
oily fish
tuna, salmon, sardines
10-25% fat
dark coloured flesh
good source of omega 3
white fish characteristics
- Large proportion of white fibres - Low content of myoglobin
- Low oxygen supply
- Anaerobic energy
- Burst swimming - Fatigue quickly
Oily fish characteristics
Large proportion of red fibres
- High level of myoglobin
- High blood supply
- Endurance muscles allowing fish to swim long distances - Aerobic energy
- Mitochondria and myoglobin
- Fat reserves used as energy sources
Types of shellfish characteristics
- Crustacean - shell turns orange when cooked 2. Molluscs - shell opens when cooked
Why do crustaceans change colour
- The exoskeleton contains carotenoid astaxanthin - Obtained through diet
- Accumulates on the shell and in the flesh
- Covered by blue crustacyanin protein resulting in blue/black colour
- During cooking the crustacyanin disappears as it denatures revealing the astaxanthin
(more heat stable)
nutritional benefits of seafood
contains all essential amino acids
good source of omega 3s (EPA and DHA)
- B group vitamins
important for cell metabolism
A+D vitamins (oily fish)
minerals (Phosphorus, calcium, iodine)
Fish muscle arrangement
- Arranged in sheets to allow undulation of their bodies through the water
- Thin layers of short muscle fibres
- Thin weak connective tissues between muscle
layers
Rigour mortis - muscle
- Muscle that was once pliable becomes rigid during rigour then once it passes out of rigour it becomes pliable again
Factors affecting onset - Species
- Whitening take 1-2 hours
- Muscle fibre composition
- Condition
- Degree of exhaustion
- Capture procedure (net v line(fight more))
- Size
- Temperature
How rigour affects shortening
- If conditions are too extreme prior to energy depleting eg. higher temperatures at rigour there is strong contraction
- Fish can be frozen or pass through rigour whens stored in ice
Gaping
- Meat quality defect
- Breaking of weak connective tissue
- Caused by rapid muscle contractions at high temp and rough handling - Results in flaking of the muscle
- Can increase microbial spoilage
How rigour affects handling and processing
Processing prior to rigor:
- Minimise shrinkage by freezing immediately after fillets have been cut from pre-rigor fish
- Otherwise shrinkage of up to 60% can occur leading to increased toughness pre and post cooking and increased water loss leading to dry product
Processing during rigor:
- Muscle is too rigid for processing during rigor
Processing after rigor
- Majority of fillets cut after rigor
- If the fillet remains attached to the skeleton shortening is reduced (similar to tender
stretching in mammals)
- Freshness of fish affected by length of rigor
Ways to minimise the effect of rigour
- Keeping fish chilled at every stage
- Potential to raise temp under controlled conditions to accelerate rigor but higher risk
that gaping may occur if temp is too high or held for too long
Chemical changes
- Autolytic reactions – multiple enzymatic reactions (e.g. proteolysis) to digest tissue - Fish and seafood is high in PUFA – lipid hydrolysis and oxidation
- Leading to rancid odours
- Colour changes (browning and discoloration)
- PUFA oxidise at faster rate
- Leads to shorter shelf life
Bacterial spoilage
Two main causes
1. Inappropriate storage conditions 2. Prolonged storage pre-cooking
- Leads to changes in muscle structure, off flavours and odours
Fish
sustainability v nutrition
mackerel and sardine are the best (less than 1% adults)
Food waste and food loss
- Fresh produce is perishable so susceptible to wastage and loss
- Food loss typically refers to food lost through the supply chain because of damage,
disease, non-compliance with standards - Food waste typically refers to edible food discarded either before or after spoilage - 1/3 of all food is wasted (spoilage, political reasons) – FAO
- 20% of food wasted in Australia
- Important to extend shelf life, reduce spoilage, reduce wastage
What is spoilage
- The deterioration of food - becomes unfair for human consumption - physical, chemical and biological
- Spoilage has an important ecological function bu compromises safety and increases waste
Shelf life
- Amount of time product is acceptable/safe for consumptions - varies from person to person
Factors that affect microbial growth
intrinsic and extrinsic
Intrinsic factors
- pH
- Moisture content
- Water activity
- Redox potential
- Physical structure
- Nutrient availability
- Presence of antimicrobial agents
Extrinsic factors
- Temperature
- Relative humidity
- Gas atmosphere
- Microorganisms present in food
Proteolysis and putrefaction
- Proteolysis - hydrolysis of proteins resulting in oil odours from compounds containing sulphur and ammonia
- Putrefaction - anaerobic breakdown of protein
- Yields foul smelling diamine compounds
Spoilage of meat
- Slime, discolouration, bad odour
- Many genera of bacteria, moulds and yeasts found on
fresh meat but only a few involved in storage
MIlk spoilage - ecological succession
- Lactococci - ferment lactose to lactic acid - pH drops - growth of lactococci inhibited
- Lactobacilli - grow at lower pH - continue to ferment lactose to lactic acid until growth is inhibited - proteins precipitate at low pH
- Yeasts and moulds - grow at low pH - metabolise acid
- Bacillus species - metabolise remaining proteins into ammonia - pH rises - bad
odours
Spoilage of F&V
- Postharvest fungi have important ecological functions, but affect the volume, storage, shelf life etc.
- pH range of a large number of vegetables well within growth range of bacteria
- pH of fruits tends to be more acidic so favours growth of fungi
- Genetic susceptibility
- Maturity and ripeness
- Temperature and moisture
- Handling, storage
- Mostly fungi, some bacteria (pH, sugar, redox potential)
- Infection may originate
- As endophytes (e.g. Fusarium)
- From inoculum in the field (e.g. Botrytis, Monilinia)
Intrinsic factors - pH effects
- The internal pH of almost all cells is near neutral
- pH affects enzymes and transport of nutrients into the cell
- Ability to proliferate at high or low pH depends on ability to change environmental pH - A pH on either side of the optimum results in longer lag phase before growth
F + V Careful handling
- Ifnection through ruptured oil glands during harvest and post-harvest handling - Management
- Clean shed
- Avoid damaging fruit
- Washing
- Fungicide sprays or dips - Waxing
