Proteins- Notes

Proteins

Amino acids

• Proteins are polymers (many subunits) of amino acids

• held together by peptide bonds

• 20 different amino acids

  • Central carbon

  • Amino group

  • hydrogen

  • variable group

    • this is the difference

Multiple Choice

What element do proteins have that carbohydrates or fats do not?

• Carbon

• Nitrogen

• hydrogen

• oxygen

Structure: 4 levels of organization

❖

Peptide bond: the covalent bond between the carboxyl group of one
amino acid and the amino group of the next amino acid.

❖

Each level refers to a polypeptide until you describe a functional protein

❖

Structure: 4 levels of organization

❖

❖

Primary structure: the sequence of amino acids

❖

• Secondary structure : twists and turns resulting from

  • amino acid side chains interacting with each other

  • interaction with the environment

    • Similar to putting shoes in a box- heel to toe.
      

❖

Tertiary structure: twists and turns fold to form a functional protein.

❖

• A folded and functional polypeptide is now a protein

• stabilized by hydrogen bonds and disulfide bridges that occur between non-adjacent amino acids.

❖

• Hydrophobic and hydrophilic interactions help maintain the shape of a protein

• Some proteins are complete and functional at this level

❖

Multiple Choice

Any string of string of amino acids is referred to as a protein even if it is not a functional level of organization.

• true

• false

❖

Quaternary structure: some proteins are made of subunits to be a
fully functional protein. (like a football team has offense, defense,
special teams, etc.)

❖

The structure of the protein is responsible for the function of the
protein

❖

When a protein is folded and functional, this is called its native or natural structure.

❖

Most of what we do with proteins in food will denature them. This
means they are unfolded and not functional.

Denaturation

❖

The tertiary and quaternary structure is described as the native form.

❖

When a protein unfolds, or tightens, it is described as denatured and is
non-functional.

❖

Denaturation: the unfolding or inactivation of a protein.

❖

• Denaturation can be done:

• mechanically (whisking, electric mixer, kneading)

• change in pH

• change in temperature (either hot or cold)

• exposure to ultrasonic sound waves.

Multiple Choice

Coagulated (clumped) proteins in your body would be very bad. Therefore, denaturation must precede coagulation.

• true

• false

Denaturation

Many of the changes observed when preparing proteins is caused when proteins coagulate or clump

​denaturation must precede coagulation

• necessary for many components in food

• changes we describe when food is cooked

Multiple Choice

When you boil an egg, what happens to the proteins?

• first they coagulate, then denature

• sugars cross-link with fats

• proteins denature, then cross-link and gel

• the proteins break apart into amino acids

Multiple Choice

What are sources of proteins?

• Meat and poultry

• eggs

• beans

• Mushrooms

• all of these

Multiple Choice

What else can be a source of protein?

• Nuts and seeds

• Bread

• dairy products

• all of these

Proteins in our food

❖

• Proteins provide structure: in baking, gluten (a protein in wheat) is formed when flour gets wet, this provides the elastic property to dough which is utilized in leavening.

• kneading a dough will develop gluten's elasticity

• mixing flour too much develops too much gluten, interferes with leavening
  
  

❖

Different wheat flours have different amounts of gluten based of gluten based on the type of wheat and how the wheat is ground. Whole wheat flour contains the germ and the seed coat, which is why it has a coarser texture

​Wheat flour

Types of wheat flour

• Bleached: exposed to various chemicals which damages some of the starches and proteins,

• whitens faster than unbleached

• easier to work with than unbleached flour.

All-purpose flour has 10-13% protein and is good for most products

Specialty flours:

have different amounts of gluten and yield a different quality product.

Cake flour: 8-9% protein, yields a softer cake, it is also less likely to collapse with a high
sugar:flour ratio, it is also whiter than all-purpose bleached flour

Bread flour: has about 14% protein, yields a denser bread

Proteins in our food continued

❖

Gels, such as gelatin (jello) are formed when heating or melting causes the proteins
to denature and cross link, forming a firm structure

○The proteins coagulate when they crosslink

○Then it attracts water (like starch gels).

○Remember proteins must denature before they can coagulate.

○Proteins are Emulsifiers

○Because some proteins have both hydrophobic and hydrophilic parts, they can
provide the stability to form a permanent emulsion.

○

Proteins in our food continued

❖

Foams: such as whipped cream or meringue.

○Meringue is egg whites beaten until stiff and stabilized with cream of tartar (acid).

■ Beating the egg whites mechanically denatures the protein

■Cream of tartar changes the pH, which further denatures the proteins, allowing a more stable foam, it
also makes the foam whiter.

○The foaming ability depends on temperature, whipping cream will foam better if cold, while eggs will foam
better if at room temperature. For egg whites, a glass or metal bowl is preferable to a plastic bowl.

■The plastic might be rough and break the bubbles

■Or have residual fats which interferes with the foaming ability

○

❖

Texturize: as in forming meat substitutes or in making cheese.
➢

Fish has more connective tissue between muscle fibers and is flakier than beef or chicken.

➢

Cuts of beef with more connective tissue than other cuts of beef are less tender

❖

Enzymes are a special type of protein that catalyzes chemical reactions.

❖

Enzymes are responsible for:
➢

fruit turning brown,

➢

the fermentation caused by yeast or bacteria

➢

important for tenderizing meat.

Meat

• Meat and poultry from muscles that are used more, such as legs and shoulders, will have tougher muscle fibers and more connective tissue.

• This is important for consider how to prepare the meat such as how to tenderize it or the best method of cooking.

Cooking Proteins

❖

Two methods of cooking proteins are used, both refer to the medium used to
transfer energy

❖

Moist (or wet) method uses water, such as boiling, simmering, or steaming

❖

Dry method uses air or oil, such as in baking or frying (anything that is not
water)

❖

When cooking meat, the connective tissue breaks down at a higher
temperature than muscle, the challenge becomes how to cook both proteins
without drying out the muscle. Lower temperatures for a longer period, or
higher temperatures for a shorter period. This is why using a moist method
can be beneficial for a desirable melt-in-your-mouth texture.

Multiple Choice

Why does fish and seafood have a different texture than land animals?

• life is easier in water

• more connective tissue between muscle fibers

• Both of these are correct