Food Chem Quiz 3

Front 1

Draw the chemical structure of a triglyceride.

Back 1

Front 2

Provide the short name forlinolenic acid (N:M format) and then draw this fatty acid structure.

Back 2

18:3n3

Front 3

In plant oils, in whatlocation on the triglyceride is this fatty acid (linolenic acid) most often found?

Back 3

SN2

Front 4

Describe two structural or functional differencesbetween saturated and unsaturated fatty acids.

Back 4

-Saturated fatty acids have no double bonds between molecules while unsaturated do.

-Saturated fatty acids acids have all of their available electron donor and acceptor spots filled with hydrogens, only some spots of unsaturated are filled.

- Saturated fats are solid at room temp, unsaturated are liquid

Front 5

What does the terminology omega-3 fatty acidmean?

Back 5

Omega-3 fatty acids: A class of essential fatty acids found in fish oils, especially from salmon and other cold-water fish, that acts to lower the levels of cholesterol and LDL (low-density lipoproteins) in the blood. (LDL cholesterol is the "bad" cholesterol.)EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are the two principal omega-3 fatty acids. XXX

Front 6

Describe two common structural changes thatoccur in lipids during hydrogenation and how these influence the Tm of thelipid.

Back 6

– Saturated bonds and Cis to trans conversion

- This leads to higher melting tempeatratures

Front 7

When comparing butyric, stearic, oleic, andlinoleic fatty acids, identify which has the highest Tm and describe why thisis so.

Back 7

Stearic has the highest melting point because it is saturated and it has the largest chain. This is so because it it saturated and has more carbons than the others.

Front 8

Identify and describe the 3 main types of lipidcrystal structures. Which is most stable? Which has the highest melting temperature?

Back 8

Simple(Nonpolar esters of fatty acids with alcohols), compound (Lipids that contain fatty acids and anothercompound) and derived(Mixed group of lipids). Simple is the most stable. Simple has highest melting temp

Front 9

What characteristics of phospholipids andmonoglycerides contribute to their function as emulsifiers?

Back 9

Phospholipids act as emulsifiers because they can surround droplets of oil, allowing them to remain suspended in a watery environment.

Front 10

Interesterification

Back 10

Also called randomization• Def. Rearrange fatty acids so they becomeevenly distributed randomly amongtriacylglycerol molecules of the fat

-To improve consistency and usefulness

Front 11

Explain thedifferences in melting points between Caproic and stearic acids

Back 11

Stearic is about 70 C, Caproic is much loweer

Front 12

What form(liquid or solid) would you expect the following food lipids to demonstrate at4ºC, 21ºC, and 37ºC? Why? Coconut lipid Salmon lipid Milk lipid Chicken lipid Olive lipid

Back 12

Coconut - solid, solid, liquid

Salmon - liquid, liquid, liquid

Milk- solid, solid, liquid

Chicken - solid, solid, solid

Olive- liquid, liquid, liquid

Front 13

Describe the influences ofchain length, crystal structure, and degree of unsaturation on the meltingpoint of lipids

Back 13

Longer and straighter the chains:the higher the MP

As degree of unsaturation increases:MP decreases- Oils: high content of unsaturated FA

Trans FA have:higher MP than cis (pack more tightly)

Front 14

Describe thecharacteristics of alpha, beta, and beta prime lipid crystals

Back 14

Beta crystals higher MP than beta prime, alpha crystals lowest MP (dueto less crystalline and more disordered /randomstructure)

Front 15

How do emulsifiers decrease interfacial tension?

Back 15

With the help of surfactants. It mediates interactions between hydrophobic and hydrophilic interactions

Front 16

Hydrogenation is one of themost prevalently used chemical reactions in the fat processing industry. What factors influence this reaction?

Back 16

• Increases theresistance tooxidation and flavordeterioration

• Increases the meltingpoint of the oil/fat

Front 17

Explain the differences in melting points between palmitic and palmitoleic acids

Back 17

palmitic is about 64 degrees C, palmitoleic acid is 1 degree C

Front 18

Explain the differences in melting points between n-octadecanoic, cis-9-octadecenoic and trans-9-octadecenoic acids.

Back 18

n-octadecanoic is Stearic acid and 70 degrees c, cis-9-octadecenoic is 6 degrees C, trans-9-octadecenoic is 37 degrees C

Front 19

Polymorphism

Back 19

Polymorphs are different crystal forms of the same chemical substance.

Transformation of one polymorph into another can occur with orwithout melting the solid.

Front 20

Primary attractive force between nonpolar lipids?

Back 20

Van der Waals

Front 21

Whatare the four main bonding forces present within and between proteins? For each type of bond, give an example of oneamino acid with a side chain that can participate in that type of bond.

Back 21

Peptide bond, hydrogen bond, covalent bond, ionic bond.

XXX

Front 22

Describethe pKa of an ionizable amino acid and why it is important forprotein structure and function in a food

Back 22

Proteins are more stable against denaturation at theirisoelectric point than at other pHs

XXX

Front 23

Whatis the common covalent crosslink found between proteins? Explain how and why this crosslink is oftenbroken and reformed during processing.

Back 23

- Important in stabilizing structure; intra- andintermolecular bonding

– Sulfhydryl-disulfide interchange reactions important inbreadmaking and other food applications.

XXX?Generally, when a protein solution is heated to a progel stateand then cooled, interactions take place

Front 24

Defineand describe protein denaturation. Someproteins are heat-stable and resistant to being denatured. In terms of amino acid composition orstructure, propose one explanation for heat-stability.

Back 24

- Any major modification in theconformation (2, 3, or 4o) not accompanied by disruptionof the primary structure (peptide bonds);

- Ultimatelyresulting in total unfolding of the protein

Heat – causes sharp transition from native to denaturedstate (can measure as a thermal transition). Hightemperatures favor hydrophobic interactions.Susceptibility of proteins depends on many factors -nature of the protein, protein concentration, water activity,pH, ionic strength, kind of ions present

Front 25

Ifyou were designing a protein to have good solubility properties, what are 2aspects (amino acid types, or 2o or 3o structures) thatyou would incorporate into the protein structure?

Back 25

Casein is an example of a protein that exists unfolded and isstable to most denaturants, including heat

XXX

Front 26

Whydo most proteins lose some of their solubility characteristics at theirisoelectric point (pI)? Why doesaddition of heat usually enhance precipitation at a proteins pI?

Back 26

No electrostatic repulsion

Proteins may aggregate and precipitate

XXX

Front 27

What makes aprotein a good emulsifier?

Front 28

Why woulddeamidation of glutamine and asparagines increase water solubility?

Back 28

Glutamine residues may be acted on by an enzyme calledtransglutaminase, which catalyzes the cross-linkingbetween glutamine and a primary amino group.?

Front 29

What islysinoalanine and briefly explain how it forms?

Back 29

• lysinoalanine formed from lysine anddehydroalanine – lose lysine availability andis toxic

Front 30

You have a soyprotein isolate (~90% protein content). How would you go about making texturized soy protein?

Back 30

Thermal coagulation and film formation – e.g.,concentrated soy protein solutions, hydrophobiccereal prolamin proteins

Front 31

From starchstarting material, name 2 enzymes that are used to make high-fructose cornsyrup

Front 32

What is theaction of lipase, and for what is it used in the industry?

Back 32

Catalyst = enzyme lipase

Front 33

What 2 reactantsare required for the Maillard browning reaction?

Back 33

Amino containing compound and reducing sugar

Front 34

What enzyme catalyzeshydrolysis of fatty acids from the glycerol molecule?

Back 34

enzyme lipase

Front 35

What does the food industrydo to prevent hydrolytic rancidity from occurring in processed foods?

Back 35

• Lower temperature• Inactivate enzymes• Choose fats for formulations carefully– Short chain fatty acids (<12C) arehydrolyzed faster than longer chain

Front 36

How do emulsifiers decreaseinterfacial tension?

Back 36

The system is stabilized by an emulsifier thatslows the separation rate of the dispersed phase

Front 37

Why are polyunsaturated fatty acids more susceptible to autoxidation than saturated fatty acids?

Back 37

Double bonds?

Front 38

What four physicalproperties of lipids affect the crystallization of a food fat? Explain these relationships.

Back 38

Mechanical properties, mouthfeel, physical stability, visual apperance

Front 39

Hydrogenation is one of themost prevalently used chemical reactions in the fat processing industry. What factors influence this reaction?

Back 39

Def: a reaction betweenhydrogen gas and unsaturatedfatty acids in the presence ofcatalysts (nickel, platinum,palladium) that results in amore saturated fatty acid

Front 40

Define and givetwo examples of each of the traditional classifications of proteins.

Back 40

CompositionHomo/hetero(conjugated)-protein

ConfigurationFibrous/globular

SolubilityAlbumin/globulin/glutelin/prolamine/etc

Sourcemeat/milk/egg/plant

Front 41

List the amino acids thathave charged and polar side chains. Draw their structures. Do the same for those that have uncharged andpolar side chains and those that have nonpolar side chains.

Back 41

Charged and Polar AA• Aspartic acid, glutamic acid, • lysine, arginine, histidine

Uncharged and Polar AA• Asparagine, glutamine, cysteine, glycine, serine,threonine, tyrosine SOLUBLE IN WATER

Front 42

What is the primarystructure of a protein? What bonding force(s) maintain(s) this structure? Whatdetermines this structure?

Back 42

Linear sequence of amino acids joined bypeptide bonds

Partial double-bond of peptide bond hasstructural implications

Resonance structure precludes protonation ofthe peptide N-H group

Front 43

What is the secondarystructure of a protein? What bondingforce(s) maintain(s) this structure?

Back 43

Spatial structure the polypeptide chainassumes along its axis (due to sequence ofAA and side chain structures)

α-helix, β-sheet, β-turn

Front 44

What is the tertiarystructure of a protein? What bonding force(s) maintain(s) this structure? Whatdetermines this structure?

Back 44

3-dimensional organization of thepolypeptide chain

Covalent bonds stabilize tertiarystructure

Most importantly is the relocation of the hydrophilic residues,especially the charged residues, at the protein-water interface

Front 45

Whatis the quaternary structure of a protein? What bonding force(s) maintain(s)this structure?

Back 45

Association of more than onepolypeptide chain, known assubunits, to form dimers,trimers, tetramers…

structure is determined by

– electrostatic interactions

– hydrogen bonding

– hydrophobic interactions

– disulfide bonds

– between the R groups of aminoacids that are in contact on thesurfaces of the associatingprotein chains

Front 46

Define denaturation of aprotein. Why is it important to the foodscientist?

Back 46

Any major modification in theconformation (2, 3, or 4o) not accompanied by disruptionof the primary structure (peptide bonds); ultimatelyresulting in total unfolding of the protein

Effects include:

– Decreased solubility resulting from unmasking ofhydrophobic groups

– Altered water-binding capacity

– Loss of biological activity

– Increased susceptibility to attack by proteases– Increased intrinsic viscosity

– Inability to crystallize.

Front 47

What are some of the functional propertiesresulting from protein manipulation and processing?

Back 47

1. Hydration (or hydrodynamic) properties(dependent on protein-water interactions)– Related to water absorption and retention• wettability• swelling• adhesion• dispersibility• solubility• viscosity (thickening)

2. Related to protein-protein interactions– precipitation– gelation– formation of various other structures (doughs, etc.)

3. Surface properties– surface tension– emulsification– foaming

Front 48

What determines the tertiary structure of aprotein? What characteristics aredetermined by the tertiary and quaternary structure of a protein?

Back 48

the relocation of the hydrophilic residues,especially the charged residues, at the protein-water interface

free energyof the molecule is reduced to the minimum value possible

Front 49

What determines the solubility of aprotein? Specifically, how is solubilityimpacted by pH, salt concentration and protein denaturation?

Back 49

Solubility may be increased in a protein by: – Changing pH – Low level of salt – Low level of heat (to 40oC) – Partial hydrolysis –

Front 50

Define the term gel. What types of gels are usually found in foodsystems? How can we differentiatebetween these two gel systems?

Back 50

an intermediate phase between a solid and liquid– a “substantially diluted system which exhibits nosteady state flow”

Thermally reversible gels are sustained primarily bynoncovalent interactions (gelatin)

Because hydrophobic bonds are strong at hightemperatures, these gels are generally thermallyirreversible (egg-white gels)

Front 51

Listand discuss the factors that influence water binding capacity of proteinsolution.

Back 51

At low concentrations (<0.2 M), salts increasethe water binding capacity of proteins

Partial hydrolysis leads to Increased water binding andemulsification properties

Protein denautration alters water-binding capabilities

Front 52

What is an emulsion? How are proteins involved in forming a stableemulsion? What makes a protein a goodemulsifier?

Back 52

• Emulsions are the macroscopic dispersions of twoimmiscible liquids

ROLE OF PROTEINS ON FOAMING& EMULSIFICATION• Lowers surface & interfacial tensions dueto adsorption at the interface- ease of formation of foams & emulsions• Stabilizes foams & emulsions

Front 53

What properties of aprotein cause it to have good foaming properties?

Back 53

Lowers surface & interfacial tensions dueto adsorption at the interface

Foamability of different proteins depend ontheir rates of adsorption and their ability tounfold at the air-water interface

Solubility of protein– More soluble form better foams

• Ability of protein to:– Rapidly diffuse and adsorb at the interface– Rapidly unfold (denature) at the interface– Stabilize (via intermolecular interactions) in a cohesive film at theinterface

• Surface hydrophobicity of protein– Hydrophobic regions of protein orient towards nonpolar air phase

• Partial denaturation– More easily unfolds at air interface

• Presence of lipids– May interfere with foam formation (0.03% egg yolk in egg white)

• Processing parameters (energy input, shear, time)

Front 54

Define emulsion. Describethe characteristics of a good emulsifier.

Back 54

• Emulsions are the macroscopic dispersions of twoimmiscible liquids

Behavior of protein at interfaces (O/W & A/W)• Interfacial behavior depends on physicalinteractions- primary structure as well as conformation- denaturation

Factors Affecting Protein-BasedEmulsions• Temperature• Salts• Processing parameters– Energy input (shear), droplet size, lipid type,temperature• Protein– Solubility, surface hydrophobicity and charge,flexibility, elasticity, ease of unfolding• External phase– viscosity

Front 55

Define foam. Describe thecharacteristics of a good film forming protein.

Back 55

a mass of small bubbles formed on or in liquid, typically by agitation or fermentation.

Factors Affecting Foaming

Solubility of protein– More soluble form better foams• Ability of protein to:– Rapidly diffuse and adsorb at the interface– Rapidly unfold (denature) at the interface– Stabilize (via intermolecular interactions) in a cohesive film at theinterface• Surface hydrophobicity of protein– Hydrophobic regions of protein orient towards nonpolar air phase• Partial denaturation– More easily unfolds at air interface• Presence of lipids– May interfere with foam formation (0.03% egg yolk in egg white)• Processing parameters (energy input, shear, time)

Front 56

Define gel. Describe thecharacteristics of a good gel forming protein.

Back 56

A gel is an intermediate phase between a solid and liquid– a “substantially diluted system which exhibits nosteady state flow”

Will gel in hot and cold

Front 57

Write the equation forStoke’s Law. Define each term.

Back 57

V = (2gr^2(d1-d2))/(9pi^2)

Front 58

Define each of thefollowing heat-induced changes in proteins. Identify which are common and whichare uncommon in food products.1. denaturation2. aggregation3. gelation4. precipitation5. thermal degradation6. hydrolysis7. oxidation10. maillardbrowning

Back 58

1. Denaturation - Losing 2,3,4 structure and unfolding to end up at highest energy level state.

Front 59

Describe the heat induced changes in the following proteinfunctional properties:1. hydrophobicity2. solubility3. emulsifying capacity4. gelation capacity5. foaming properties6. enzyme activity

Back 59

Emulsifying Capacity:– Measured as the volume of oil that can be emulsifiedper gram of protein in an oil-in-water (O/W) system

Hydrophobicity– Surface hydrophobicity of proteins mayincrease or decrease after heating

Solubility is a chemical property referring to the ability for a given substance, the solute, to dissolve in a solvent

Gelation Capacity:– The amount of water that can be bound ortrapped per gram of protein

Enzyme Activity:– Temperature controls the rate of enzymecatalyzedreactions and influences enzymestability

Front 60

You are working in R&Dfor a major food company and have been assigned the task of improving thequality of your protein-based foam/emulsion/gel product because the product isphysically destabilizing before end of shelf-life

What ingredients are used to stabilize thefoam/emulsion/gel? How do they work?

Back 60

Gel: Some gels are also stabilized by disulfide crosslinks

Emulsion : Two phases will rapidly separate unless there is anadsorbed surfactant present at the interface to stabilize itby protecting against close contact and association ofindividual globules

Foam: Soluble cereal proteins stabilize bubbles (gas cells)before starch gelation stabilizes the crumb structure

Front 61

You are working in R&Dfor a major food company and have been assigned the task of improving thequality of your protein-based foam/emulsion/gel product because the product isphysically destabilizing before end of shelf-life

What might be causing thedestabilization of your foam/emulsion/gel?

Back 61

Heat

Front 62

Lipids in foods are most often structured as free fatty acids.

True or False?

Back 62

False. Triglycerides

Front 63

Saturated fatty acids contain double bonds connecting carbons.

True or false?

Back 63

False. Only unsaturated have double bonds

Front 64

Trans fatty acids are always unsaturated.

True or false?

Back 64

True

Front 65

Type of chemical bond that links fatty acids to glyceride to form lipids?

Back 65

Ester bonds

Front 66

Compared to starch, lipids are...

Back 66

Smaller, hydrophobic

Front 67

In fatty acid chains, define N:M

Back 67

N = Carbon

M = Double Bonds

Front 68

Omega naming system for fatty acid # carbons from double bonds, label from carboxy end.

True or False?

Back 68

False, From Methyl end

Front 69

Most common fatty acid in foods

Back 69

Oleic (18:1)

Front 70

Trans fatty acids are more linear than cis fatty acid counter parts

True or false?

Back 70

True

Front 71

Milk fats are unique because...

Back 71

Contains shorter chain fatty acids than other animal fats

Front 72

Lipids from plant sources generally have unsaturated fatty acids in SN2 position

True or false?

Back 72

True

Front 73

Fully hydrogenated fats contain trans fatty acids

True or False

Back 73

False

Front 74

In an o/w (Oil in water) emulsion, continuous phase is....

Back 74

Water, oil is the disperesed

Front 75

Butter is what kind of emulsion

Back 75

Water in oil

Front 76

Stokes Law describes

Back 76

Emulsion stability, Creaming rate velocity

Front 77

Increasing viscosity of continuous phase in an emulsion slows rate of separation

True or False

Back 77

True

Front 78

Increasing attractive van der waals forces between fatty acids increase melting temp

True or false?

Back 78

True

Front 79

Why does steric acid have the highest melting temp?

Back 79

Longest, no kinks, most van der waals attraction

Front 80

Solid-State transformation of one lipid crystal type to another is called...

Back 80

Polymorphism

Front 81

Polymorphism can occur even if lipids don't melt

True or false?

Back 81

True

Front 82

Hydrolytic rancidity is caused by...

Back 82

Lipase

Front 83

Identify the statement related to hydrolytic rancidity

Back 83

Fatty Acids are cleaved off of glycerol molecule

Front 84

Identify Rancidity traits

Back 84

Presence of lipase speeds up, reaction end products are hydroperoxides

Front 85

Hydrolytic & oxidative rancidity results in same changes to lipid structure

True or false?

Back 85

False

Front 86

Presence of oxygen can contribute to...

Back 86

Lipid oxidation

Front 87

Compare monounsaturated fatty acids to poly unsaturated acid

Back 87

Have lower Tm, oxidate more quickly

Front 88

Initiation of lipid oxidation occurs more quickly than propagation

True or False

Back 88

False

Front 89

What initiates lipid oxidation?

Back 89

Singlet oxygen, chlorophyll, lipoxygenase

Front 90

Many antioxidants are molecules that are oxidized preferentially to lipids

Back 90

True

Front 91

Peptide bonds are covalent bonds that are stronger than disulfide bonds, that are also covalent.

True or false?

Back 91

True

Front 92

Charged/Polar mean it is hydrophillic

True or False

Back 92

True

Front 93

Denaturation is defined as loss of primary and secondary structure

True or False

Back 93

False

Primary structure is not typically denatured, would be extremely difficult to do

Front 94

Alpha helicals are more stable than beta sheets,

True or false

Back 94

False

Front 95

Proteins can be denatured by

Back 95

Heat, pH, mechanical sheer

Front 96

Compared to native globular protenins, denatured proteins are

Back 96

Characterized by increased viscosity and is more digestible

Front 97

Globular proteins are more sensitive to environment than fiberous proteins

True or False

Back 97

True

Front 98

Proteins are least soluble at...

Back 98

ph = pI

Front 99

pH lower than pI leads to what charge?

Back 99

Positive

Front 100

pH higher than pI leads to what charge?

Back 100

Negative

Front 101

Proteins from different sources have different structures and properties

True or False

Back 101

True

Front 102

Protein bond strength

Back 102

Highest to lowest

- Amine

- Disulfide

- Hydrogen

- Ionic

- Hydrophobic

- Van der Waals

Front 103

Identify one mech by which an emulsion can be stabilized

Back 103

By increasing viscosity of continuous phase