Transcript Fish and Shellfish - The Beacon School

Fish and Shellfish
Health benefits
• Omega 3s – vital for brain and retinal
function, reduces inflammatory response.
• Humans have a hard time synthesizing
Omega 3s, must acquire from diet.
• Omega 3s being put into other foods…
questionable health benefits.
• Fish is often lean meat: low fat, high
protein.
Health Risks
• Toxins/pollutants – PCBs and heavy metals:
lead, cadmium ,mercury.
• Above substances interfere with transmission of
neuronal signaling, damage brain and liver.
Cannot be destroyed by cooking.
• Microbes – Vibrio, Botulism, Hepatitis A/C
• Shellfish acquire toxins by coming in contact
with dinoflagellates (use toxins for chem.
warfare).
• Parasites – Anasakis, tapeworms and flukes
Health risks 2
• ‘Waxy fish’ – Escolar, Walu and Orange
Roughy contain ‘wax esters’ which are a
combination of a long-chain fatty acid and
a long-chain alcohol.
• We lack the enzymes to break down this
substance and so it passes intact through
our GI tract leading to diarrhea.
Fish morphology
• Fish can dispense with large heavy skeletons
and lots of connective tissue. WHY?
• Mostly white flesh for explosive bursts of speed
(water’s resistance to movement increases
exponentially with speed)
• Thin band of red flesh for sustained slow speed
swimming.
• Fast long distance swimmers have larger amts
of red (tuna, etc.)
• Pink flesh is white flesh with some myoglobin
added.
Fish Flavor – saltwater vs.
freshwater
• Saltwater is 3% salt by
weight but fish need to be
~1% salt by weight.
• Achieve isotonic balance
by storing solutes: glycine
– sweet, glutamic acid (as
MSG) – savory, unctuous.
• Problem comes from
storing TMAO and urea
(salty and bitter) which
rapidly deteriorate into
TMA and ammonia.
• Freshwater fish need to
pee constantly to remove
excess water but..
• Do not store solutes and
therefore are milder
tasting when fresh or old.
Fish oils
• Fish are designed to operate at cold
temperatures and therefore need fats that do not
congeal easily (cell membranes would stiffen
and prevent normal cellular operation).
• Lipids are therefore unsaturated (highly kinked)
and stay liquid until very cold temps are
reached.
• Cows can have saturated fats because they
operate at much higher temps.
Fish Spoilage
• Fish enzymes and bacteria are used to
operating at low temps.
• Refrigerator feels balmy and therefore fish
spoils at lower temps than other meats (in
which enzymes and associated bacteria
work at higher temps).
• Cold water species/fatty species spoil
faster than tropical/lean species.
Cooking Fish
• Fish are delicate and fragile (WHY?) and
must be cooked with care.
• Flesh tends to fall apart when cooked and
fish can dry out rapidly (WHY?).
• Fish can vary dramatically from season to
season.
• Fish that have finished long swims tend to
mushy (they actually digest their own
muscle for food).
Fish Anatomy
• Skin/scales – protective, sometimes
coated in mucus.
• Bones – spine, ribcage. Also fin bones and
‘pin’ bones (help direct forces through
fishes body). Can be softened and eaten.
• Guts – livers, swim bladders, ‘tongues’ are
prized as delicacies.
Fish muscle
• Arranged in myotomes – short bundles
with interleaved connective tissue
(myosepta).
• When cooked myotomes separate into
‘flakes’.
• Tail region has more gelatin and fat and is
therefore more succulent.
• Fat content of muscle ranges from 0.5%
(cod) to 20% (herring).