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Alaska Seafood Processing Leadership Institute 2011/2012

Lecture Notes: Dr. Chuck Crapo Fish/Shellfish as Food:

What Do We Know

Different from Other Animal Proteins (Primarily in Structure)

Specific Texture Attributes

Limited Shelf Life

Hundreds of Species with Different Characteristics

Nutritional Benefits

Omega-3 Fatty Acids

Balanced Amino Acid/High Protein Content

High Sterol Levels (Shellfish)

Consumption Related to Reduced Heart Attacks Fish Muscle

Three types - striated, smooth and heart. Mostly interested in the striated muscle that makes up the flesh of the fish. Smooth muscle is used in the edible portion of some mollusks.

Two types of striated muscle found in fish - white meat and dark meat.

Dark meat (also called swimming meat) lies just under the skin. Shape and amount depends on the species. Fish that live on the bottom of the ocean have very little or no dark meat. Fish swimming neat the surface have higher amounts. Used for continuous movement.

White meat used for quick bursts of energy, such as fleeing predators.

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Structure

myotomes - mixture of myofibril bundles filled in by sarcoplasmic proteins

myocommata - connective tissue in sheathes between myotomes Major Components of Seafoods

The three major components of fish and shellfish are

-- Water -- Protein -- Lipids

These make up as much as 95% of the total composition

Average Proximate Composition

Water 75% Crude Protein 15% Fat 5% Ash 5%

Water and fat usually combine for 80% of the total.

Water

Muscles contain 50% to 85% water, depending on species and condition

Plays important roles - solvent for organic and inorganic materials - reaction media for enzymes - hydration of proteins (texture)

Water binds with many of the proteins (hydrophilic residues) - mainly hydrogen bonding as well as some covalent bonds.

Water also involved in hydrophobic molecules (on proteins and lipids) to form ordered structures

These forms comprise bound water that is not easily lost

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Also free water that is lost during freezing/thawing, during storage and handling as a result of handling and physical damage

Water is critical to

- processing characteristics - texture - nutritive value - sensory quality - shelf life

Crude Protein

Crude protein refers to the total of nitrogen containing compounds in a sample. This includes proteins, volatile amines, enzymes, free amino acids, urea, nucleic acids, and nucleotides.

Muscle proteins are of three classes:

- sarcoplasmic - myofibrillar - stroma

Sarcoplasmic Proteins

- water soluble proteins found in the extracellular fluid and are about 30% of

the total amount of proteins in fish muscle

- include albumins, lipoproteins, blood proteins, glycoproteins and enzymes.

Myofibrillar Proteins

- salt soluble structural proteins that make up the "flesh" and are 40-60% of the total crude protein content in muscle.

- important in rigor mortis, water binding ability, texture and functional

properties

- components are myosin, actin, paramyosin (some shellfish).

- myosin and actin combine to form actomyosin

- small amounts also present are tropomyosin and troponin. These compounds regulate muscle contraction, but are not important in fish

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muscle as food

Stroma Proteins

- those proteins remaining after sarcoplasmic and myofibrillar proteins are removed. Mainly connective tissue - collagens. Make up the myocommata

- collagen make up 3% of total muscle proteins

- content depends on condition of the fish. Not used so becomes higher in

starved fish where other proteins are being used.

- also found in the skin. - has large effect on fish muscle as food. Contributes to tensile strength of

muscle and influences functional and rheological properties. Important in quality of fish fillets and muscle.

Lipids

Lipid content is used to classify fish from lean to fatty

Lipid content of fish muscle refers to the total amount of the following compounds: - phospholipids - sterols - triglycerides - wax esters

Phospholipids Small but constant amounts

Important structural role in cell membranes and metabolism

phosphotidylcholine phosphotidylethanolamine phosphotidylserine sphingomyeline

Sterols

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mainly cholesterol in molluscs and shellfish, a wide variety of sterols are present.

Triglycerides

the main energy source for fish and shellfish

Wax Esters

used for buoyancy

found in large quantities in deep water fish

Fatty Acid Composition

more complex than other animals and plants

fatty acid chains mainly from C14 to C24

consist of mainly unsaturated fatty acids, even down to the C14 and C16

the C20 and C22 acids contain 4, 5 or 6 double bonds (PUFAs)

most of the marine fatty acids are the n-3 type, very few n-6 type

composition in any fish depends on diet, season, sea temperature, physiological condition and other factors the two most important fatty acids are the 20:5 (EPA or eicosapentaenoic acid) and 22:6 (DHA or docosahexaenoic acid)

these are the fatty acids that are linked to reduced heart disease and associated problems.