Week 5 Food Composition and Function

What is special about proteins?

they are the most diverse class of bio-molecules; typically large molecules

Where do we see proteins appear in foods?

animal origin: mean, poultry, dairy, eggs, fish. Plant origin: nuts, legumes

What are proteins considered?

macronutrients

What are proteins made up of?

amino acids- 20 found in nature

What are proteins primarily composed of?

carbon, hydrogen, nitrogen, oxygen; only macronutrient that contains nitrogen and primary source of nitrogen in out body

What is the solubility of proteins like?

not always soluble, can form colloidal suspension

What is some current reasearch in proteins?

plant based proteins- sensory perception challenges

What are the functions of proteins in foods?

affect texture, firmness, structure and taste; water binding; emulsification; gelation; color (malliard reaction)

What are the functions of proteins in nutrition and biology?

4 kcal/gram, main structural material in body, enzymes, receptors and transporters, antibodies, regulatory functions, synthesis of biologically active compounds 

What does protein quality depend on?

amino acid composition and digestibility

What are the components of an amino acid?

alpha carbon, amino group (NH2), hydrogen, acid (COOH), functional group unique for each amino acid (determines it’s properties

What amino acids are hydrophilic?

when the functional group is acidic or basic

What amino acids are hydrophobic?

when the function group is a hydrocarbon chain

What are most amino acids structurally?

chiral with the exception of glycine

Why are natural amino acids L?

because it’s better for protein structure

What is pl (isoelectric point)?

the pH at which the amino acid is electrically (net) neutral

What happens to amino acids at low pH?

the amino group gains a H and the N on it get’s a positive charge 

What happens to amino acids at high pH?

the carboxylic acid group acts as a acid and gives up a H

What is the zwitterion amino acid?

an amino acid that despite having an overall neutral charge contains both a positive N and a negative O on the amino group and the carboxylic acid group; occurs at neutral pH

What does the side chain of the amino acid determine? 

properties of the amino acid: nonpolar-hydrophobic or polar -hydrophilic (noncharged polar or charged polar is possible)

What does someone mean when they say essential amino acid?

it can’t be synthesized by humans 

How is the protein/ amino acid digestion score determined?

content of essential amino acids and how well they are digested and absorbed in the small intestine, the comparison for this is egg=100 and something GMOs have to do is improve their score 

What is the bond between two amino acids called?

peptide bond- type of covalent bond

How does a peptide bond form?

through a dehydration reaction from the H on the amino group and the hydroxyl group on the carboxylic acid- H2O is a product

What determines the final structure and shape of proteins (protein folding) and thus functional properties? 

the sequence of amino acids

What is the primary structure of protein? 

includes the number and order of amino acids eg Ala-Gly-Pror

What is the secondary structure of proteins?

includes the folding of the protein due to hydrogen bonds eg alpha helix, beta sheet, random coil 

What is the tertiary structure of proteins? 

complete folding pattern, 3D structure, specific to the protein 

What is the quaternary structure of proteins?

interaction of subunits (many tertiary structures together) , final level of an organization

What are tertiary structures stabilized by?

disulfide bonds (covalent, between cystines), ionic (salt) bons between charged side chains, hydrogen bonds, hydrophobic interactions and van der waals forces 

How do alpha helixes form? 

hydrogen bonds between the H on an amino group and the O on the carboxyl group of different amino acids in different locations in the polypeptide bond

How do Beta sheets form?

when two or more polypeptide strands, called beta-strands, align and are held together by hydrogen bonds between the carbonyl oxygen of one strand and the amide hydrogen of another

What are the types of simple (non-conjugated) proteins?

globular proteins (spheroproteins)and fibrous proteins

What are some examples of globular (speroproteins)?

albumins (eggs) and globulins (meat) both are water soluble

What are characteristics of globular (spheroproteins)? 

usually soluble in water and they yield only amino acids by hydrolysis 

What are examples of fibrous proteins?

collagen, keratin, myosin

What are characteristics of fibrous proteins?

usually insoluble in water, elongated shape

What are conjugated proteins?

combination of another molecules/group with the proteins

What are examples of conjugated proteins?

lipoproteins, phosphoproteins, metalloproteins, glucoproteins, nucleoproteins, mucoproteins, chromratoproteins

What are proteins sometimes called?

molecular giants- because the molecular weight of protein is very high up to 10^6 daltons 

Because of their size what can proteins do?

form colloids, may cause light scatter and turbidity in a product and scatter light (why milk is white and soups are cloudy)

What is denaturation of proteins?

unfolding of the tertiary and secondary structures of a protein

What happens chemically when denaturation happens?

Hydrogen bonds break

What does not change during denaturation?

the backbone

What is denaturation not?

a reversable process

What is coagulation?

clotting/precipitation of denatured proteins

What does coagulation form?

gels

What is coagulation caused by?

heat (egg solidification), acids (yogurt), agitation (whipped cream stabilization), enzymes (cheese curdles) polyphenols, salts  

What does the amphoteric nature mean for amino acids?

they have both acid and base properties 

Becuase of their amphoteric nature what can proteins do? 

behave like buffers at pHs close to pKa (ph<5;>9). Charged and thus can migrate under and electric field (basis of electrophoresis). Can make salts with anions and cations.  

What does the charge of an amino acid depend on? 

the pH

What does the solubility of a protein depend on?

the pH. Lowest solubility is at isoelectric point (zero net charge = minimal electrostatic repulsion) 

What reduces solubility of proteins?

salt concentration (something else dissolved = reduce capacity to dissolve other stuff) 

How does gel formation work?

trap water in 3D network and solution; solution state to solid like state by heating 

How do gels form more specifically?

in the progel state functional groups are exposed; upon cooling there is a reduced kenetic energy favors stable non-covalent interactions between them

What properties of food does gel formation affect?

texture

What happens to proteins in gel formation?

protein remains dispersed

What does gelling efficacy depend on?

protein structure; some proteins can gel at 1% (gelatin) others need more (eg 10%)

What is foaming?

a type of colloid with an aq continuous phase and a gas (air)

How does foaming happen? 

gas is trapped in protein films; protein stabilize the interface between liquid and air 

Why do proteins foam?

because they are amphiphilic; hydrophobic parts stick out towards the air and their hydrophilic parts stay in the water helping them to stabilize the bubbles

What does foaming do to food?

it can enhance palatability of food but is not always desirable (lab)

How can protein affect texture?

it can increase the stickiness of foods like in dough

How does protein affect viscosity?

can be used as a thickening agent in foods ie thick sauces, gravies, soups

What are examples of protein being used in emulsification? 

mayonnaise, salad dressing, gravies, ice cream 

How are proteins used in viscoelasticity of bread?

bread dough proteins (glutenin + gladin) form gluten when mixed with water which creates a stretchy elastic network that traps gas

What does glutenin provide?

strength and elasticity

What does gliadin provide?

extendibility and stretch

What ingredients can weaken gluten by diluting it?

fiber, sugar, fat

What are the main structural components of pancakes? 

minimal gluten (batter isn’t kneaded) and structure is mainly from egg proteins and starch giving a soft fluffy texture 

How does hydrolysis occur in proteins?

using several hydrolytic compounds such as acids (stomach acid), bases, enzymes (proteolytic enzymes: peptidases, proteinases)

What occurs during hydrolysis of proteins?

the cleavage of backbone chain upon the addition of a water molecule

Why is hydrolysis of proteins used in industry?

required to make water soluble products high in protein (>4.7%) and to balance solubility, absorption rates, flavor (taste better) 

What parts of the amino acid does hydrolysis involve? 

COOH and NH2 groups, sometimes side chains 

What is hydrolysis of proteins important for?

Maillard reaction and enzymes in biological functions

What should food proteins be?

easily digestible, non-toxic, nutritious, available, sustainable

What is the general steps of protein to food?

protein —> denatured —> “something” (gel/foam/sticky matrix) —> finished food

What doe the amino acids in animals meet?

better meet the need for amino acids in our body than plant proteins with the exception of soy proteins

What are some plant based proteins?

cereal are good sources of proteins but poor in lysine and legumes are good sources but poor in sulfur amino acids (methionine, cysteine)

What are complementary proteins? 

combining foods that compensate for each other amino acid gaps we get all essential amino acids 

What are is an example of complementary protein foods? 

cereals are low in lysine but rich in methionine and cystine and legumes are rich in lysine but low in methionine and cystine; by combining these two reach the requirements for amino acids