Food Chem Midterm #2

energy, sweetness, texture, controls moisture

what do carbohydrates provide in foods?

starch, lactose, sucrose

70-80% of the calories in the human diet come from these carbohydrates: __, __, & __

Cx(H2O)y

general formula of carbohydrates

monosaccharides

carbohydrate molecules that cannot be broken

down to simpler carbohydrates by hydrolysis; simple sugars

disaccharides, oligosaccharides, and polysaccharides

monosaccharides are building blocks for more complex structures

hydrogen

lots of hydroxyl groups in monosaccharides means lots of __ bonding

D

naturally occurring glucose is designated as the ___ form

isomers

molecules with the same chemical

formula but different chemical structures

stereoisomer

molecules containing the same atoms

(bonding connections) but different spatial

arrangement

enantiomers

compounds which are mirror images of each other

diasteromers

isomers that differ about one or more asymmetric

carbons (not a mirror image)

chiral

molecules are considered ___ if there is

another molecule of identical composition but

arranged in a mirror image which is not

superimposable

asymmetric

___ carbons are usually the feature of a

chiral molecule

isomerization

process by which one molecule is

transformed into another molecule which has the

same atoms, but different spatial arrangement

aldoses, ketoses

___ and ___ with equal number of C

atoms are isomers of each other

acetal

hydroxyl in a hemiacetal can react further

with a hydroxyl group of an alcohol to form an

___

pyranose

six-membered cyclic monosaccharide ring

furanose

five-membered cyclic monosaccharide ring

anomer

diastereoisomer of cyclic forms that differs in configuration only at C 1 for aldoses and C2 for ketoses

equatorial

bulky OH groups and hydroxymethyl group are

in the ___ position because this is more energetically favored

tautomers

interconverting forms are called ___

amide

the ___ bond is the determiner of function

lipo

egg yolk contains ___proteins

food

___ proteins are easily digestible, nontoxic, and contain all essential amino acids

21

proteins contain up to ___ different primary amino acids

R

physiochemical properties depend on the chemical nature of the ___ group

L

all proteins in nature contain only ___-amino acids

ampholytes

___ behave both as acids and bases

isoelectric point

pH = ___ (PI)

2 or more

___ amino acids joined by peptide bond form a peptide

aliphatic, aromatic

these amino acid groups are hydrophobic and have limited solubility in water

polar

these amino acid groups are soluble in water and can be charged or uncharged

primary structure

linear sequence of amino acids, basis of all higher structures, formed by COVALENT bonding (peptide linkages)

secondary structure

periodic spatial arrangement of amino acid residues at certain segments of the polypeptide chain; helix or extended sheet-like structures

parallel

in helix structure, the H-bonds are oriented ___ to the helix axis

perpendicular

in pleated sheets, the H-bonds are oriented ___ to the direction of the chain

tertiary structure

protein folds further into a compact 3-dimensional form, stabilized by non-covalent bonds or covalent bonds (disulfide)

amino acid

shape of the protein molecule is dictated by its ___ sequence

quaternary structure

stabilized by non-covalent bonds, spatial arrangement of a protein when more than one polypeptide chain is present

covalent

there are NO ___ bonds in quaternary structure

dimerized

___ protein shields the hydrophobic amino acids from water

protein structure

___ stability is a thermodynamic state that maximizes favorable interactions and minimizes unfavorable ones

free energy

to maintain stability in protein structure, ___ will be at the lowest point possible

hydrophobic

the driving force of protein folding is ___ interactions

aqueous

the major reason that proteins fold into unique tertiary structures is so the majority of the nonpolar groups are removed from the ___ environment

denaturation

weakening bonds can cause ___

pH, ionic strength, temperature, solvent composition

any change in ___, ___, ___, and ___ can cause protein denaturation

primary

protein denaturation causes major changes in the secondary, tertiary, and quaternary structure. NEVER to the ___ structure, unless there are extreme conditions to cleave peptide bonds

globular

protein that decreases as denaturation increases; unfolds and becomes less soluble

fibrous

protein that increases collagen to gelatin conversion in meat cooking

solubility, chemical activity of reactive groups, susceptibility to enzymatic hydrolysis, enzymatic activity, altered water-holding capactiy

denaturation affects: (5)

increases

chemical activity of reactive groups ___ as inner R-groups are exposed in denaturation

enzymatic

peptide bonds become more available for ___ hydrolysis, they can be cleaved and digested by enzymes

decreases

with protein denaturation, enzymatic activity ___, such as when vegetables are blanched to denature degradative enzymes

decrease

protein has a natural ability to hold onto water, but denaturation can ___ this water-holding capactiy

reversible

in protein structure, native to denatured is ___ if not severe

non-reversible

in protein structure, denatured to aggregation is ___

coagulation

when protein completely comes out of solution; insoluble & irreversible

irreversible denaturation

when unfolded peptides are stabilized by interactions with other chains

aggregation continues

eggs get rubbery when overcooked because

B to C

at what stage in this diagram is the denaturation irreversible?

heat

___ is the most commonly used denaturing agent in food processing; has a strong effect on them

reversible

when pressure is used to denature proteins, the process is highly ___ because proteins are very flexible and compressible

shear

___ is used to denature proteins via shaking, kneading, whipping, etc to incorporate air bubbles and foster adsorption of proteins to the air-liquid interface

isoelectric point

proteins are most stable to denaturation at the ___

repulsion

when at the PI, there is a lack of ___ between proteins, which allows for more protein-protein interaction and aggregation to occur

neutralization

a low concentration of salt, or "salting in" proteins, allows for the ions to interact with proteins, creating electrostatic ___ that stabilizes the protein structure

water

a high concentration of salt, or "salting out" proteins, the ions instead compete with protein to bond with the ___, leading to more protein-protein interactions, and aggregation

collagen

___ helps to hold muscle fibers and bundles together

reduce

protein denaturation and fiber shrinkage can ___ water retention

gelation, emulsification, foaming, water binding, heat coagulation

animal proteins allows for functions such as: (5)

limited, do not

plant proteins are used to a ___ extent in foods as they ___ perform as well as animal proteins in terms of functionality

hydration

___ is a protein functionality that affects solubility, dispersibility, swelling, thickening, and water-holding capacity

surface activity

___ is a protein functionality that affects emulsification and foaming

rheology

___ is a protein functionality that affects elasticity, viscosity, cohesiveness, chewiness, adhesion, gelation, dough formation, texturization

cannot

functionality properties ___ always be predicted because proteins never exist alone

hydrophobic, ionic interactions

protein solubility is influenced by ___ & ___

decreases

hydrophobic interactions ___ solubility

increases

ionic interactions ___ solubility

greater

the fewer # of surface hydrophobic groups on the surface means ___ solubility

amphiphilic

many food products are foam or emulsion type products and require an ___ substance at the interface

emulsification

proteins are desirable for ___ because they rapidly adsorb at interface, unfold & reorient @ interface, and interact with the neighboring molecules forming the viscoelastic film

flexibility

molecular ___ is the most important characteristic of proteins

surfactant

proteins serve as ___ in a liquid surrounding air droplets

conformation

during foam formation change in ___ of protein denatures

gel

a continuous three dimensional solid-like cross-linked network of (protein) molecules embedded in an aqueous solvent

water entrapment, immobilization

2 functions/properties of gels are ___ & ___

sol

non-covalent bonding groups for network bonding are limited in this stage of gelation

progel

viscous liquid, protein denaturation and polymerization have occured, functional groups capable of H-bonding or hydrophobic bonding are exposed, protein network formation can occur in this stage of gelation

gel

progel is cooled and the decrease in thermal kinetic energy facilitates formation of stable non-covalent bonds (H-bonding, hydrophobic, or electrostatic interaction in this stage of gelation

reversible

___ gel networks are sustained primarily by non-covalent interactions (H-bonds); upon reheating they will melt to progel state; ex: gelatin

irreversible

___ gel networks are formed primarily by hydrophobic interactions; ex: egg white gels

coagulum

___ gels are proteins with large amounts of non-polar amino acids, occur when aggregation rate is faster than denaturation rate, irreversible

translucent

___ gels are proteins with small amounts of nonpolar amino acids, soluble complexes upon denaturation, and the gel network forms upon cooling

gluten

___ is the main storage protein

gliadin, glutenin

gluten is a heterogenous mixture of the proteins ___ & ___

amino acid

gluten's properties are due to the ___ composition

gluten proteins absorb water & unfold partially; hydrophobic interactions and sulfhydryl-disulfide interchange reactions occur; polymers interact with each other

process of gluten formation: 3 steps

glutenins

polypeptide polymers joined by disulfide cross-links, able to polymerize via sulfhydryl-disulfide exchange; elasticity; cohesiveness

gliadins

contain cysteine residues, exist as intra-molecular disulfide bonds, no sulfhydryl-disulfide interchange; expansion of dough; extensibility