L5 Structure and Taste

What drives protein into its 3D structure?

water drives proteins into its folding structure

• putting protein in water, you decreased entropy because there’s less water to freely roam around, however when you fold that protein up you increase entropy in water because now there is more room

• if water is taken away then it unfolds

What happens when a protein whose 3-D structure is the result of water reaches an interface? (ex: line between water and not water)

proteins will denature and unfold spontaneously

Why is water less dense when it is frozen than when it is liquid?

• as a liquid it is free to form hydrogen bonds with all it’s neighbors (and it frequently does so) and it net compresses the liquid

• forms a lattice that is spread out as ice

What allows for egg white foams to be stable?

• egg whites contain 90% water and 10% protein

• once whipped the air is beaten in and the protein starts to uncurl

• some parts of the protein like water and stick to it and some parts do not, and these stick to the air bubbles

• the unfolded protein surrounds the air bubbles at the interface and stabilizes the foam network

What happens during the process of homogenizing milk?

• you make the large globules of fat/oil naturally present in milk small

• protein unfolding on the surface of those globules stabilize it

What are protein films?

unfolded proteins can have beneficial properties however, when proteins unfold/denature on surfaces they can polymerize creating a protein film if not cleaned

• can in turn lead to biofilms of bacteria

• properties of films depend on the protein, concentration, and the kinetics at the interface

How can salt act as a denaturant of proteins?

proteins whose 3-D structure is the result of charge interactions can unfold as salts are added

What is an example of a protein that can be denatured by salt?

muscle proteins

• charges are the basis of the ability to move therefore any changes in ionic concentrations charges of the water will cause the protein to unfold

What is the practical application of muscle proteins and it being denatured by salt?

• muscle proteins and salts help to produce processed meat products (hot dogs)

What six things can alter the environment and thus cause the denaturation of protein?

• solvent: if we change the solvent the proteins can denature

• temperature: adding energy starts to unfold the 3-D shape

• charge/pH: affects ionic status of proteins affecting ionic interactions

• pressure: unfolds

• shear: some are so delicate that just shear itself unfolds it

• combinations

How does heat alter protein structure?

biopolymers are in the native state at the body temperature of the organism and if you move above it then it will begin to denature and form new networks (sometimes aggregation)

• ex: starch

  • starch granules → hydrated starch from water → starch gel from heat

Is the temperature of denaturation the same across all proteins?

no it differs

• defined by the structure of the protein and the properties of the solvent

How do you determine the melting point/denaturation point of a protein?

via calorimetry

• provides accurate measurements of heat exchange within a system and monitors the denaturation process

What happens when you fry an egg?

classic example of protein denaturation

• when placed in heat, the albumen protein in the egg whites denatures and unfolds

• new disulfide cross linking occurs and this causes aggregation and this causes the egg to become an opaque white

What are four consequences of protein denaturation?

• three dimensional networks: sometimes turn into gels, films, precipitates

• loss of biological activity: enzymes, receptors, antibodies no longer function

• loss of bound ligands: minerals, prosthetic groups, vitamins and cofactors (does not mean that it is not getting absorbed but also can’t say that it is not getting absorbed)

• digestibility: typically digestibility increases, plants typically are hard to digest as an evolutionarily established mechanism

What is the one exception in which where more heat would cause a protein to be less digestible?

milk protein

Describe how we utilize controlled protein denaturation in order to give rise to the structure of meat we want.

seen in sous vide and slow barbecue

• one gives rise to a fibrous structure that we want

• collagen based proteins give rise to the tough, rough, and rubbery properties of meat that we don’t want

  • the protein that we want have a higher denaturation temp than collagen based proteins so we tend to cook meats at a temp between the collagen based protein denaturation temp and the fibrous promoting protein denaturation temp

How do we utilize protein denaturation in order to create cottage cheese?

• in milk casein micelles are stabilized due to negative surface charge

  • net neutralization of charges at the isoelectric point eliminates repulsion and proteins aggregate and this is what causes the formation of cottage cheese

How does pressure denature proteins?

high pressure alters the properties of water as a solvent, resulting in the denaturation of proteins

Overall what do protein structures provide to foods?

• three dimensional networks via gels, doughs, cheeses

• interfacial stability via emulsions and foams

• fibers via meat substitutes

What is the issue with eating animal based products compared to plant based products?

it costs a lot more land, water, and nutrients to grow animals than to grow and eat the plants straight up

• not sustainable

What have we tried to do in order to combat the unsustainable eating of animal based products?

have impossible foods (nonmeat products made from plants) that make use of heme like structures found in plants to give the same color and feel as meat

• problem: no one likes it (the taste I’m assuming)

Pre 20th century how was fat primarily obtained? Who had access to it?

saturated fats were obtained animals (e.g. butter, lard, tallow)

• expensive as they were extracted from animal tissue

• high valued

• available only to the rich

Most of the cuisines that used fat as a functional ingredient were developed from where? Give an example.

France

• examples

  • ice cream, puff pastries, french fries

Why is the structure of fat (ex: having long chain fully saturated triglycerides) significant?

the crystal network provides distinctive structure, texture, mouthfeel, stability, flavor release, and latent heat of melting

Describe the structure of butter and fat spreads.

• spreadible solids

• 3-D network on annealed crystals that hold layers of oil

• structure that is unique to animal products

Early 20th century how was fat primarily obtained? Who had access to it?

fats were made primarily via hydrogenation of vegetable oils (got rid of unsaturated bonds)

• still highly valued

• cheap

• available to everyone