Midterm 2

Question 1

What are true solutions?

Answer 1

• Very small particles/ions dispersed in a liquid
• Constant kinetic motion
• Homogenous because evenly distributed
• Very stable, does not form a gel

Question 2

What are colloidal dispersions? What are the stabilizing factors? What happens under certain conditions?

Answer 2

• Intermediate sized macromolecules (proteins, cooked starch, pectic substances)
• Less kinetic motion
• If dispersed particles H bond with each other, will precipitate out of colloidal dispersion (GEL)

Stabilized by:

• Brownian movement: random movement of particles as they are constantly and unevenly bombarded by water molecules
• Repelling: dispersed molecules are negative and scatter
• Water of hydration: layer of water molecules attached to surface of particles by weak hydrogen bonds prevent contact and bonding between colloidal particles

Question 3

What are suspensions?

Answer 3

• Large dispersed particles or groups of molecules
• Include starch in cold water or fat globules or temporary emulsions
• Very unstable as gravity causes dispersed particles to separate upon standing
• Do not form GELs

Question 4

What is the composition of starch?

Answer 4

• Contains glucose units joined up

- Starch molecules: amylose and amylopectin

Question 5

What are the sources of starch?

Answer 5

Roots

• Eg. potatoes, arrowroot, tapioca
• Found in plastids in cytoplasm

Cereal

• Eg. wheat, rice, corn
• Found in endosperm of grain

Question 6

Talk about the formation of a SOL for starch. Mention suspensions too.

Answer 6

• When starch is placed in cold water, it forms a suspension
• During heating, the suspension is transformed into colloidal dispersion
• Gelatinization: irreversible swelling of starch granules when heated in water
• Kinetic energy of water molecules increases, breaking H bonds holding amylose and amylopectin together
• Water moves into starch granule and they expand (membrane breaks)
• Some amylose molecules diffuse out while amylopectin stays in
• Membrane only allows linear molecules through
• This creates a thick but pourable SOL (thickened mixture which can be poured from container, molecules move randomly, distributed evenly)
• Increase in viscosity and translucency

Question 7

Talk about the formation of a GEL for starch.

Answer 7

• Retrogradation: setting of cooled gelatinized starch SOL to form a GEL
• Reduction in kinetic energy
• Amylose molecules which diffused out form H bonds with other amylose molecules, surface of starch granules and branches of amylopectin molecules sticking out of granules

Question 8

Talk about syneresis for starch.

Answer 8

Leakage of liquid from gel

• Aging during prolonged storage or continuing to cool causes shrinkage of GEL because additional bonds are formed, which squeezes out water
• Freezing then thawing a gel (expansion breaks H bonds formed by amylose, letting water trapped to leak out)
• Cutting a gel (breaking starch molecules that were full of water)

Question 9

Discuss waxy cornstarch.

Answer 9

• 100% amylopectin
• Forms SOL but not a GEL because no H bonds
• Same thickness before and after going into freezer (no H bonds)

Question 10

What are the factors affecting SOLs and GELs for starch? What should you do?

Answer 10

1. Concentration of starch
   - More starch/amylose = thicker SOL, firmer GEL
2. Source of starch
   - Cereal starches = more amylose = thicker SOL, firmer GEL
3. Cooking temperature
   - Overcooking = bursts swollen granules = gummy, thinner SOL
   - Use double boiler or oven poaching to keep temperatures under 100 C
4. Acid
   - Ruptures swollen starch granules, causing water to leave
   - With heat = hydrolysis of SOME amylose and amylopectin into dextrins (short chain glucose molecules) which can’t form GELs
   - Decrease in thickness but still same translucency of SOL
   - Decrease in GEL firmness
   - Add acid after gelatinization but before retrogradation
5. Sugar
   - Add sugar after gelatinization but before retrogradation unless you want less thick/firm SOL/GEL

SOL:
- Sugar competes with starch for water = decrease in thickness
- Sugar forms H bonds with starch = gelatinization temperature goes up
- Protects swollen starch granules from rupturing due to overheating or acid
GEL:
- Decrease in GEL firmness
- Forms H bonds with starch granules and excess water = stabilizes gel (less syneresis)

Question 11

What is lumping for starch and how do you prevent it?

Answer 11

• Gelatinized starch granules outside with raw, ungelatinized granules inside

To prevent, granules must be separated completely:

• Dry mixing starch granules with sugar (when added to liquid, sugar dissolves and allows liquid to surround each granule completely)
• Suspending starch granules in cold liquid (then heated)
• Mixing starch granules with melted or liquid fat (in a roux, fat coasts granules)
• AND stir constantly to allow water to move into all starch granules to create colloidal dispersion

Question 12

What is the difference between the white and brown sauce?

Answer 12

• In brown sauce, flour heated without moisture (dry heat)
• Amylose and amylopectin hydrolyzed into dextrins
• Cannot form a GEL, only a SOL
• React with each other to form non-brown pigments in a non-enzymatic browning reaction

Question 13

What are the types of proteins?

Answer 13

Simple

1. Globular: rounded in shape
   - Ovalbumin in egg whites
   - Lactalbumin and lactoglobulin in milk
   - Gliadin and glutenin in wheat
2. Fibrous: coiled/extended in shape
   - Collagen and elastin in connective tissue of meat
   - Myosin in muscle of meat

Conjugated/complex proteins: composed of simple protein and nonprotein material

1. Phosphoproteins (protein + phosphoric acid)
   - Casein in milk
2. Glycoproteins (protein + carbohydrate)
   - Ovomucin in eggs
3. Lipoproteins (protein + fatty substance)
   - Lipoproteins in egg yolks + whipping cream
4. Chromoproteins (protein + coloured material)
   - Myoglobin in muscle of meat

Question 14

What is the structure of proteins?

Answer 14

• Primary: amino acids linked by peptide (covalent) bonds to form polypeptide chains
• Secondary: spring-like coiling of polypeptide chain (simple fibrous proteins)
• Tertiary: helix folds back on itself to form globular structure (simple globular proteins(
• Quaternary: globular proteins combine with each other or non-protein substance (conjugated/complex proteins)

Question 15

Discuss isoelectric point of proteins.

Answer 15

MEASURED IN PH.

• Carboxyl group donates H, amino group accepts H
• The point where amino acid no longer has electric charge
• Like charges of protein no longer repelling each other
• Least stable = denatured
• Protein molecules are attached and form H bonds with each other to create larger molecules
• Cannot stay in colloidal dispersion

Question 16

Discuss the factors of denaturation/coagulation.

Answer 16

1. Change in pH to IEP
2. Increase or decrease in temperature (cooking/freezing)
3. Mechanical action (whipping, beating)

Question 17

What is denaturation, coagulation, and over-coagulation?

Answer 17

Denaturation: change from naturally ordered configuration of protein molecule to more randomly structured molecule (H bonds break)

Coagulation: new H bonds form at new locations among polypeptide chain within protein molecule (most common cause is heat)

Over-coagulation: polypeptide chains compress together and squeeze out water due to excessive H bond formation

• Result due to prolonged exposure to pH (usually decrease), heat (too high or too long), mechanical action (unlikely)
• To prevent, use double boiler or oven poaching to keep temperatures under 100 C

Question 18

What is the composition of eggs?

Answer 18

White: more water, 80% protein (albumins), no fat/carbohydrate
Yolk: ½ water, ½ solid (⅓ protein and ⅔ fat), lecithin, cholesterol, no carbohydrate, more minerals/vitamins

Question 19

How are eggs stored?

Answer 19

• Fresh eggs broken onto a flat plate stand up in rounded force due to viscosity of thick portion of egg white
• Lose moisture = air cell between two membranes to enlarge
• Lose CO2 = egg white becomes alkaline, thins out
• Egg yolk absorbs water from egg white and yolk membrane stretches
• When broken onto a plate, deteriorated egg yolk flattens and egg spreads
• Chalazae has disintegrated and can’t hold yolk in centre
• To prevent this, keep in original carton to prevent moisture loss and absorption of odours due to porous shell
• Can be refrigerated for 2 weeks

Question 20

What are the functional properties of eggs?

Answer 20

Thickeners (SOL)
Gelling agents (GEL)
Foaming agents (egg whites)
Emulsifiers (lecithin in egg yolks)

Question 21

Discuss the SOL/GEL formation for eggs.

Answer 21

• With heat, the protein becomes denatured
• Coagulation will occur in which unfolded polypeptide chains will form new H bonds at new sites along polypeptide chains
• Will result in formation of GEL if egg mixture is not stirred because formation of H bonds is not disrupted
• Will form SOL if egg mixture is stirred during coagulation because disrupts formation of new H bonds along unfolded polypeptide chain

Question 22

What are the factors affecting SOL/GEL for eggs?

Answer 22

1. Temperature
   - Egg white proteins coagulate easier than egg yolk proteins
2. Amount of egg proteins
   - Diluting egg solution keep egg proteins further apart = less thick/firm SOL/GEL
   - Higher temperatures needed for denaturation and coagulation
3. Sugar
   - Forms H bonds; reducing bonding between actual egg proteins
   - Slower rate of denaturation and coagulation
   Increase in coagulation temperature
   - Protect against over-coagulation
   - Less chance of curdling/syneresis
   - Decrease SOL/GEL thickness/firmness
4. Acid
   - Contributes H ions which neutralize negative charges around egg protein molecules
   - Egg proteins reach IEP and denature/coagulate faster
   - Decrease in denaturation and coagulation temperatures

Question 23

What is an egg white foam? Talk about baking.

Answer 23

Colloidal dispersion in which air bubbles (dispersed phase) are trapped in a liquid (continuous phase)

Beating egg whites:

• Incorporates air bubbles into liquid portion of egg whites
• Denatures egg white proteins which collect on surface of egg white bubbles
• Stabilizes foam (longer time before foam collapses)

Baking egg whites causes egg proteins to coagulate to make foam permanent (never collapse)

Question 24

What are the factors for egg foam quality?

Answer 24

1. Age of eggs (maximum volume from 2-3 days old)
2. Temperature (maximum volume from room temperature)
3. Length of beating
   - Under beating = too few egg white proteins denatured = less stable
   - Overbeating = denatured proteins are less flexible = air cells break = lower foam volume, less stable
4. Sugar
   - Form H bonds with egg white proteins, interfering with denaturation
   Increases time required to create foam and reduces foam volume if added at start of beating
   - More stable/stiff foam, preventing overcoagulation, if add at soft peak stage
5. Acid
   - H+ neutralize negative charges, allow proteins to reach IEP and denature faster
   - The more denatured proteins, the more stable/larger volume/stiffer the foam
   - Always added at beginning so foam forms faster
6. Fat
   - Delays foam formation
   - Lipoproteins in egg yolks form complex with egg white proteins preventing denaturation
   - Use glass/metal bowl instead of plastic/silicone to beat egg whites as fat adheres to plastic

Question 25

What is the grey-green colour for eggs? How do you prevent it?

Answer 25

• Hydrogen sulfide in egg whites combines with iron in egg yolk
• Forms ferrous sulfide which has grey green colour
• The longer the egg proteins are heated after coagulation, the more grey-green ring

Hard boiled:

• Slow cooling after cooking = pressure of heat allows contact between egg white and yolk
• SOLUTION: cool rapidly in cold water to reduce pressure on outside of egg drawing hydrogen sulfide in egg white away from yolk + crack eggs to remove the pressure from shell

Scrambled:

• Keeps eggs hot for too long after cooking/coagulation, allowing compounds to move around
• Iron and hydrogen sulfide come into contact while still warm for long period of time
• SOLUTION: prepare in small batches + limit heating time + minimize heat

Question 26

Can eggs freeze/thaw?

Answer 26

Whites:

• Raw: yes
• Cooked: no (tough and rubbery)

Yolks:

• Raw: no (proteins denature = thick and gummy) unless you protect proteins by adding sugar/salt
• Cooked: yes

Question 27

What are the constituents of milk in solution?

Answer 27

• Water soluble vitamins (good source of riboflavin, thiamin/niacin/ascorbic acid in small amounts)
• Minerals: ⅓ of Ca, K, Mg, Na
• Sugar: lactose which participates in Maillard browning reaction
• Salts

Question 28

What are the constituents of milk in colloidal dispersion?

Answer 28

• ⅔ of Ca, phosphorus
• Proteins: whey and casein
• 80% is casein (alpha, beta, kappa) which exist with calcium and phosphate as calcium phosphocaseinate/casein micelle
• 20% is whey proteins (lactalbumin, lactoglobulin)

Question 29

What are the constituents of milk in emulsion?

Answer 29

1. Milk fat
   - Fat-in-water emulsion (fat is dispersed, water is continuous)
   - Exists as globules kept in emulsion by emulsifying layer around fat globules composed of lipoproteins
2. Fat soluble vitamins: A & D

Question 30

What is the difference between homogenization and pasteurization of milk?

Answer 30

• Homogenization: milk is pumped under extreme pressure through very small holes to reduce size of fat globules; fine emulsion; easier to digest/opaque.white
• Pasteurization: heating to kill pathogens

Question 31

What is yogurt?

Answer 31

• Inoculated milk with nonpathogenic bacterial culture which ferments lactose into lactic acid
• pH decreases to IEP of casein (4.6) which denature and coagulate (curdles)

Question 32

How does whey denature?

Answer 32

• Heat only
• Settle out of colloidal dispersion, settle to bottom of container
• If you continue to overheat, causes whey proteins to scorch bottom of pot (white film)

Question 33

How does casein denature?

Answer 33

1. Acid
   - Casein micelles are colloidally dispersed at pH of 6.7 (milk)
   - Negative charges around casein micelle repel and keep stable
   - Adding acid lowers pH, neutralizing negative charges (0) to bring casein to IEP
   - Micelles are denatured and adhere together, forming larger unstable molecules (precipitate out of colloidal dispersion)
   - Heat accelerates this reaction
2. Polyphenolic compounds
   - Found in light coloured, low acid fruits and vegetables (potatoes, apples, asparagus, mushrooms, green peas, strong tea and coffee)
   - Remove water of hydration around casein micelles, allowing them to denature/adhere together to form large/unstable molecules
   - Precipitate out of colloidal dispersion
   - Heat accelerates reaction
3. Enzyme rennin from stomach of calves
   - Synthetically produced as chymosin
   - Optimal temperature is 40 C
   - Used to make cheese to denature/coagulate proteins
   - Removes kappa casein from casein micelle
   - Alpha and beta casein readily denature, but calcium remains in micelle
   - Weak, unstable calcium caseinate GEL forms

Question 34

How to avoid denaturation of milk proteins?

Answer 34

1. Minimize heating
   - Use double boiler (< 100 C)
   - Heat only to serving temperature (do not boil)
2. Minimize time that acid ingredient and casein in milk are together
   - Add milk just before serving
   - Last step before “serving immediately”
3. Thicken water phase around casein micelles to physically prevent denatured casein micelles from adhering together and precipitating out of colloidal dispersion
   - Starch if product involves heat (gelatinized)
   - Gelatin if conditions are cold

Question 35

What does beating cream do?

Answer 35

• Incorporates air bubbles
• Disrupts emulsifying layer around fat globules, allowing them to clump together = more stable foam (longer time before bubbles burst and collapses)
• Denatures lipoproteins in emulsifying layer which collect on surface of air bubbles = even more stable foam

Question 36

How do you make sure whipped cream foam is of good quality?

Answer 36

1. Use cream with > 32% fat because you need lipoproteins
2. Use cold temperatures (cream, beaters, bowl at 4 C or lower)
   - Fat globules become more solid which clump together more easily on surface of air bubbles (more stable foam)
   - Cream is thicker, making it easier to incorporate air bubbles (higher volume)
3. Addition of sugar near the end of beating
   - Decreases foam volume + increase time to create foam if added too soon
   - Add after partial foam is created
   Increase foam stability (longer time before foam collapses)
   - Decreases foam stiffness (softer peaks)
   - Decrease chance of over-beating (butter) + increase foam stability

Question 37

What happens when you age cheese?

Answer 37

1. Changes in texture (changes to protein)
   - Firm tough and rubbery to softer and crumby
   - Cheese blends better
2. Changes in flavour (changes to fat)
   - Mild and bland to mellow and tangy

Question 38

What are the properties of cheese?

Answer 38

• Melt: medium/high in moisture AND fat

- Blend: melt well + be aged/ripened (changes in proteins)

Question 39

What happens when you overcoagulate cheese?

Answer 39

• Too high a temperature or moderate temperature for extended period of time
• Results in tough and stringy cheese due to excessive H bond formation
• Proteins shrink and squeeze out water = water on top of cheese
• Fat emulsion breaks = oily layer on top of cheese

Question 40

What does overcoagulation do for eggs?

Answer 40

• Overcoagulation causes excessive H bond formation resulting in syneresis in a GEL or curdling in a SOL
• Tough texture in egg proteins