Proteins Flashcards
what is the most important role of protein in food?
acts as an emulsifier
what are plant sources of protein?
pulses (more) and cereal grains (less)
what is the dimer of cysteine called?
cystine (dimerize under oxidizing conditions)
food source with highest protein?
meat, fish
what is an example of a basic amino acid important in food science?
Lysine
what is an example of a polar, uncharged amino acid important in food science?
cysteine
Milk protein rich in ____ tend to brown more quickly because of the _____ reaction
lysine; Maillard Browning
What are the essential amino acids?
histidine, leucine, isoleusine, lysine, methionine, phenylalanine, threonine, tryptophan, valine
in acidic pH, the AA has a ___ charge; in basic pH, the AA has ____ charge
positive; negative
what is a zwitterion?
a neutral AA (when pH = pI)
the pH at which the charge on AA becomes neutral
isoelectric point
Why is the isoelectric point important in food?
at this point, protein can’t stay in solution so will form aggregates and precipitate out
what is casein’s isoelectric point?
pH 4.5-4.6
how is yogurt formed?
action of lactobacillus or addition of lemon juice brings the pH to pI
casein derived phosphorylated peptides that enhance vit D absorption?
caseinophosphopeptides
3 Ser, 2 Glu
34 AA residues, with antimicrobial properties that is produced during certain bacterial fermentation
Nisin
Aspartame is about _____sweeter than sucrose; it is made up of ___ and aspartate
200 times; phenylalanine, methanol
sucralose is ___ times sweeter than sucrose, and is made through selective ___ which makes a product we can’t digest
600; chlorination
what is the primary driving force behind tertiary structure formation?
thermodynamic stability in aqueous solution
what interactions stabilize protein structure?
H bond, electrostatic, disulide, and especially hydrophobic
what are the three types of tertiary structure?
globular (insoluble AA), disordered (interact well with water), fibrous (strong secondary structure)
an example of globular protein
whey
an example of disordered protein
casein
example of fibrous protein
muscle protein collagen
examples of proteins that show quartenary structure
hemoglobin (2 alpha, 2 beta) and casein (2 alpha, 1 beta, 1 kappa)
diseases that are due to protein misfolding?
BSE, Alzheimers, Parkinsons, cancers
How do you calculate True Protein Digestibility %?
(nitrogen intake - fecal nitrogen) / nitrogen intake , x 100
How do you calculate PER? (protein efficiency ratio)
gain in body weight / quantity protein consumed, x 100
how do you get PDCAAS?
mg limiting a.a. in 1g test protein / mg same amino acid in 1g reference protein x % TPD
what is the limiting amino acid?
a.a with lowest ratio relative to established amino acid requirement values for humans 2-5 yrs old
what does PDCAAS stand for?
Protein digestibility corrected a.a. score
__ protein is the only complete non-animal source of complete protein
soy
which amino acid is missing in beef?
tryptophan
wheat, rice and corn lack __
lysine
legumes lack ____
methionine
the enzyme that reacts with lipid
lipase
Enzyme found commonly in plants and animals, requiring Cu and O2 to function; catalyzes the oxidation of wide range of phenolic compounds
polyphenoloxidase (PPO)
PPO is responsible for ________; spontaneously occurring in cut fruits and veggies
enzymatic browning
what is the purpose of polyphenol activity?
as a plant defense mechanism designed to turn plant phenols into antimicrobial products in case of tissue injury
what are some ways to prevent enzymatic browning?
blanching (denature enzyme), remove O2, addition of antioxidants, inhibit enzyme by lowering pH, SO2 to stop formation of melanins
what are some ways that protein can be denatured?
heat, change pH, change solvent polarity, addition reactive comps, presence of interfaces
what are effects of protein denaturation?
loss of solubility and bio activity, gelation, conversion of globular–>fibrous structure, surface active properties
unfolding of hydrophobic portion of a protein chain in presence of ____ interface is called _____ properties
oil/water; surface active
___ enzyme, found in cow’s stomach, is involved in cheese making
Rennet
A fibrous protein derived from collagen; heat with acid/alkali to denature, cooling to ___degrees causes the coils to regain triple helical structure as a gel
gelatin; 25
gel melting is observed at around ___degrees
37
how are sausages produced?
a meat emulsion is heated to 75 degrees, making cross links and 3D gel with entrapped water and fat globs
Examples of generating protein foam
-whipping egg white–>meringue (more air bubbles means stiffer peaks)
what is surface activity?
tendency move to surface (air/water) or interface (oil/water)
how does a molecule become surface active?
must have hydrophilic and hydrophobic groups
How does surface denaturation occur?
addition of oil in a protein-water system causes the protein to unfold to move hydrophobic parts into oil phase
casein unfolds to a ________ configuration; whey maintains a ___ structure
loop-tail-train; globular
arrange these flours in increasing protein content: cake, whole wheat, gluten, all purpose, bread
cake, all purpose, bread, whole wheat, gluten
What is the process of gluten formation?
mix and knead gliadin and glutenin to crosslink via disulfide bonds
glutenin fraction determines ____ while gliadin fraction determines ___
elasticity; fluidity and stickiness
pulses contain ____ proteins that inhibit ___ when consumed raw
antinutritional; digestion
examples of antinutritional proteins?
lectins (cancer prevention); protease enzyme inhibitors
