Final Exam Flashcards
Draw structure of triglyceride provided with fatty acids
do it
Structure of STEARIC ACID
18 carbon, zero double bonds
Structure of LINOLEIC ACID
Omega-6 (18:2, Cis-9, cis-12)
Structure of LINOLENIC ACID
Omega-3 (18:3, cis-9, cis-12, cis-15)
What is the relationship between melting points and fatty acid structure?
• Melting points increase with chain length
• Decrease with increase of unsaturation
- Linear/saturated FA is packed very tight, takes higher energy to separate, so high melting point
- Unsaturated FAs are more spread out, so easier to break up - lower melting point
Describe the polarity and structure of a fatty acid
- Contains an end with carboxyl group (double bond with oxygen and then an -OH group), which performs as the acid in a system (hydrophilic)
- Other end has short or long chain of carbons with covalent hydrogen bonds (CH2)n (saturated) or form a double bond with each other (unsaturated)
What is the difference between mono-, di-, triglyceride?
MONO - one fatty acid on glycerol backbone
- Amphiphilic - glycerol wants to dissolve in water because of hydrophilic carboxyl group; fatty acid wants to dissolve in fat (hydrophobic); can carry across cell membrane; moves freely in both water base and lipid base
DI - two fatty acids on glycerol backbone with one -OH end
TRI - three fatty acids attached to glycerol
most common, because can be so many different combinations
Of mono-, di-, and triglycerides, which can be used as an emulsifier?
- mono- and di-glyceride are both amphiphilic that can serve as emulsifier.
- Tri-glyceride is hydrophobic, since it does not contain any -OH group
What type of solvents do lipids dissolve in?
Only in organic solvents
Lipids serve as a solvent for what type of compounds?
Non-polar
Non-polar mixes well with non-polar; polar well with polar
Describe the structure of a phospholipid
Third -OH group of glycerol has phosphorus group attached to it instead of fatty acid
Describe the structure and polarity of lecithin from egg yolk
- Amphiphilic, so can be used as an emulsifier
* Phospholipid, so glycerol backbone with two fatty acids and one phosphorous group
Why is lecithin an important emulsifier in many products?
Very polar structure/Amphiphilic, so can be used to bind oil and water together
When is an emulsion formed?
When two immiscible liquids are mixed together
What is continuous phase and dispersed phase of an emulsion?
- Continuous phase is the major part of the emulsion mixture
* Dispersed is the smaller proportion which you’re trying to disperse in small droplets
Describe mayo as an emulsion. Pick out the emulsifier, the continuous phase and dispersed phase
Mayo- (high fat egg yolk base you’re trying to disperse water into)
Water-in-oil emulsion
- Fat/lipids are the continuous phase
- Water is the dispersed phase
- Egg yolk/lecithin is the emulsifier
Describe milk as an emulsion. Pick out the emulsifier, the continuous phase and dispersed phase
12% fat/88% water
Oil-in-water emulsion
- Water is continuous phase
- Fat is dispersed phase
What is a free radical?
Chemical species containing one or more unpaired electrons (unstable and highly reactive). Tries to steal any electrons it can- will attack anything next to it.
Describe the free radical chain reaction from initiation to ending
• Free radical X (unknown) attacks anything next to it- usually a lipid because they have a lot of H. Grabs the electron from the lipid and leaves the lipid impaired with a single electron, becomes a free radical.
• Free radical lipid will attack any oxygen in the air/container and creates another free radical, which attacks another lipid next to it, generating a new free radical
• Continues until all the oxygen is used up
If metals exist in system the peroxidative lipid will react with metal and create its own cycle until most of the lipids become free radicals
• When free radicals bump into each other they can form electron pairs and become more stable; are not lipids anymore, are highly volatile and have a different smell (rancid)
Give basic chain reactions for lipid oxidation (initiation, propagation, and termination)
Initiation: LH + X* → L* + XH
Chain propagation:
L* + O2 → LOO*
LOO* + LH → LOOH + L*
Chain termination:
LOO* + L* → LOOL
LO* + L* → LOL
How can lipid rancidity or fat rancidity be prevented in food products?
- LIGHT
• Selection of packaging material
• Storage in the dark - OXYGEN CONCENTRATION
• Vacuum packaging
• Nitrogen flushing - HEAVY METAL CONCENTRATION
• Selection of packaging material
• Metal chelating agents (eg: polyphosphates in meat products) - ANTIOXIDANT CONCENTRATION
• Antioxidants may occur naturally in foods (vitamins D, E, and A)
• Natural or synthetic antioxidants can be added - TEMPERATURE - Storage and distribution at low temperatures
- DEGREE OF UNSATURATION - selection of fat/oil
• Unsaturated FAs become rancid quicker than saturated FAs usually
Explain how fat functions as flavor enhancer
- Adds creamy mouth feel
* Carries many different flavor compounds - a lot of flavors can only dissolve in fats (not water)
Is there a good quality fat replacer? Why/why not
No
• Fat has lubrication effect, where flavors slide on your tongue giving you creamy mouth feel
• Enhances flavor, so when replace fat a lot of flavors are removed at same time
Draw the peptide bond between two amino acids
Do it
Names of essential amino acids
- Histadine
- Isoleucine
- Leucine
- Lysine
- Methionine
- Phenylalanine
- Threonine
- Tryptophan
- Valine
How can you tell from an amino acid’s structure if it’s polar, non-polar, or electronically charged?
POLAR -
OH groups
NH groups
SH groups
NON-POLAR - Methyl groups or ring structures
ELECTRONIC CHARGED - COOH groups,
amine (NH3) groups
Describe the PRIMARY structure of a protein
Sequence of a chain of amino acids
Describe the SECONDARY structure of a protein. Describe the different forms and which type of forces they use
Local folding of the polypeptide chain into helices (a-helix) or or sheets (ß-pleated sheets)
- ß-pleated sheets - two parallel peptide chains that form H-bonds between each other
- A-helix - H and Os form hydrogen bonding between linked amino acids
Describe the TERTIARY structure of a protein. Describe the different forms
3D folding pattern of a protein due to side chain interactions from polarity
- Fibrous Protein - Often seen in connective tissues like collagen or hair
- Globular Protein - Very common (hemoglobin, whey, etc)
Describe the four stabilizing forces in tertiary proteins
- DISULFIDE BOND - when SH groups get together they form a covalent bond, completely locking the structure
- IONIC BOND - in charged groups, positive charges will attract negative changes, forming an ionic bond; hydrophilic groups will face outside surface, towards water
- HYDROGEN BOND
- HYDROPHOBIC INTERACTIONS - polar AA side chains want to be with polar, nonpolar with nonpolar, so protein eventually forms globular shape with non-polar (hydrophobic) groups hiding inside protein. When clustered together hydrophobic interactions happen
•Similar to H-bonding - weak force, not covalent bond
Describe the QUATERNARY structure of a protein
Protein consisting of more than one amino acid chain; similar interactions as are in tertiary
Provided two amino acids, be able to predict what kind of forces could occur between them (hydrophobic interaction, ionic bond, hydrogen bond and disulfide linkages)
- Hydrophobic interaction- two methyl groups
- Ionic bond - cation and anion (eg: NH3+ and O-)
- Hydrogen bond - OH group and an O
- Disulfide linkage - two S ends
What structure is lost during denaturation?
- Secondary and tertiary structures are fragile
* Primary structure is hard to change
Describe protein denaturation
Denaturation is change of shape of a protein without breaking peptide bonds
• Usually irreversible
• Denatured proteins interact with other proteins while unfolded, if forms disulfide cross-link it’s irreversible
Why does egg white (albumin) becomes opaque during boiling or frying?
• When crack the raw egg the white is transparent and a liquid/gel texture; at this point the albumin is water soluble
• Albumin contains a lot of systein (so has a lot of -SH groups)
• When start to cook it you see the egg white turning from transparent → semi transparent → opaque
- Application of heat breaks hydrogen bonds, hidden hydrophobic groups, losing its 2ndary 3rtiary structure
- Become random coils of protein
- When temperature cools, all systein is exposed to each other and forms new disulphide linkages
Describe how cheese coagulation happens using casein
Add rennin (enzyme) which works on kappa-casein of micelle and removes it, leaving only a- and ß-cassein (both of which are very hydrophobic). Because of this they cluster together, pushing water out - cheese is formed!
Describe how yogurt is formed using casein
Add a lot of acid (+ charges) into system and you will lose more and more negative charges until you reach an zero net charge on surface, thus no repelling of micelles between each other and they coagulate. pH gets as low as 4.6
Describe casein’s structure and components
Doesn’t have a regularly defined secondary or tertiary structure due to high levels of proline. So forms a ball-shaped micelle out of random coils
• Hydrophobic a- and ß-casein, and hydrophilic kappa-casein
Very heat stable
What is protein’s isoelectric point (what is casein’s isoelectric point?)
Net charge
If add more negative charges so surface of casein micelles are all negatively charged, you have a stronger repulsion and the net charge is even higher and the casein will have a higher solubility
Describe how gelatin is made
Made from hydrolyzed collagen
• Made from three amino acids twisted together, so fibrous protein that is very long a-helix
• Produce gelatin by using enzyme to break down collagen
- Is a bunch of broken peptide pieces, but still have twisted, fibrous proteins
How is gluten formed?
When you relax and stretch out the glutenin and gliadin, disulphide linkages are formed due to glutenin’s systeins, and gliadin gets pocketed inside, creating elastic dough
Describe gluten’s two protein composition
• Gliadin - water-soluble component; molecularly pretty small globular protein
What causes celiac disease
• Glutenin - water-insoluble component; long strand of a-helices with many systeins
How does myoglobin change color in different conditions? What causes it to be red?
Blue/purple?
Brown?
RED - Oxygen in myoglobin binds to iron
•Why nitrate acid is promoted in food industry - when this acid binds with iron it forms a pink color that remains unchanged
BLUE/PURPLE - If oxygen is removed, iron binds with water
BROWN - If too much oxygen/left too long iron is oxidized
Eight food allergies, be specific about the allergen
Most often caused by proteins in foods
Milk Egg Peanut Tree nut Wheat Soy Fish Shellfish
How do enzymes affect biochemical reactions?
Reduces the activation energy for a biochemical reaction to occur
- Very specific to the compounds they react with (eg: renin only works on k-casein, not a- or b-casein)
- Has optimal condition to work - pH, temperature
Do enzyme structures change after reaction?
No - enzymes are specialized proteins that speed up or start a chemical reaction without being changed by it (a catalyst - reduce activation energy needed to initiate reaction)
Describe lock-key and induced-fit model of enzymes
LOCK-KEY: substrates fit into a specific active site to form an enzyme-substrate complex
INDUCED-FIT: when substrate gets close enough it induces the active site to change its structure to match the structure, so still a perfect match. After product is released the enzyme returns to its original structure
List the factors that influence enzyme activity
- water activity
- concentration of solution
- factors that denature protein
- enzyme inhibitors
Describe how water activity influences enzyme activity
- Eg: yeast needs water to facilitate enzymatic activity
- Reactions often need to happen in a solution
- WA will affect how quickly enzymes move to work on a substrate
Describe how concentration of the solution influences enzyme activity
- When you have a low amount of a substrate compared to enzymes the reaction rate is slow
- As more substrates are added reaction speed increases
- UNTIL all active sites of enzymes are blocked, at which point reaction rate slows
What factors denature proteins? Describe how they effect enzyme activity.
HEAT
• Most animal enzymes denature rapidly at temps >40C (104F)
• Why vegetables are “blanched” before freezing
PH
• Each enzyme has optimal pH range
• Enzyme denatures if pH is too high or too low
• Eg- pepsin works best around pH 1.5-1.7; rennin pH <5.8
•Adjust pH to slow undesirable enzymatic activity
IONIC STRENGTH/ELECTROLYTES
• Work as coenzyme to promote enzymatic activity (Ca2+, Fe2+)
•Stop important enzymatic activity (Hg2+, Pb2+)
•Salt, such as NaCl, binds to enzymes of bacteria
Describe how ENZYME INHIBITORS influence enzyme activity
•Any substance that will prevent the enzyme substrate complex from forming properly
- Competitive
- Uncompetitive - substance that can bind to non-active site of enzyme making so it doesn’t work
- Noncompetitive
• Naturally exist in many food products
- Natural preservatives - block bacteria’s enzymatic activity
- Eg- conalbumin in egg white, tomatin in tomato
What are positive applications of enzymes in the food industry? Give examples
- Make food texture more appealing (eg - meat tenderizer)
- Preserve food (eg - changing into cheese)
- Aid digestion (eg - lactase in milk
What are negative effects of enzymes in the food industry?
- Enzymatic browning in fruits and vegetables
- Rotting action in foods
- Fat rancidity
Why is cellulase added during juice extraction?
To clarify citrus juices or improve nutritional value
Why can pineapple be used to tenderize meat?
Raw pineapple contains an enzyme called Bromelain that is used to make meat tenderizer.
- Rapidly breaks down the protein and muscle structure of the meat and turns it into a mush over time
- Heating neutralizes the bromelain and will prevent it from giving your proteins a bad flavor
Describe enzymatic browning in fruits and vegetables
- Occurs when enzyme oxidases reacts with oxygen to produce brown pigments
- Creates structural changes that causes produce to become mushy
How can you control enzymatic browning of fruits and vegetables?
•Store fruits in oxygen-free environment • Replace CO2 with nitrogen •Reduce injuries or bruises •Denature the enzyme by blanching •Store fruits in cold temperatures • Use preservatives - Sulfites - Ascorbic acid - Citric acid - Acetic acid
What are the most common coenzymes?
Vitamins and minerals
Describe PHYTOCHEMICALS. Where are they found? What do they do?
- Only come from plants; usually exist as pigment/color
- Do not provide energy
- Are not necessary for daily activities
- Help fight disease (eg - heart disease, cancer)
What are food sources of allyl sulfides?
onions, garlic, leeks, chives
What are food sources of flavonoids?
legumes, soybeans, chickpeas, whole grains
What are food sources of polyphenols?
blueberries, raspberries, grapes, peppers
Describe non-nutritive sweeteners. Name some.
- Provide virtually no energy
- Add sweet flavor without adding calories
- Pose no health risks when used in moderation
Include: Saccharin Aspartame Acesulfame potassium Stevioside Sucralose
Describe nutritive sweeteners. Name some.
- Sugar alcohols
- Provide1.5-30 kcal/g
- Do not promote teeth decay
Include: Sorbitol Mannitol Xylitol Maltitol
What ingredients are in the “pink pack” of sweetener
Saccharin
What ingredients are in the “blue pack” of sweetener
Aspartame
What ingredients are in the “yellow pack” of sweetener
Sucralose
What are the drawbacks/challenges of a carbohydrate-based fat replacer?
- Variety of modified starch or gums (vegetable gums, dextrins, maltodextrins, pectin)
- Mimc mouth-feel of fat
- Can not create flaky texture in baked goods (eg- form pie crust)
- Cannot replace flavor of fat - fat releases flavor slowly to your mouth; using a fat-replacer releases too strong of flavor at once when you bite into something, so people can distinguish the difference
What are the drawbacks/challenges of a protein-based fat replacer?
- Mimic the mouth feel of fat
- Has globular shape, so can roll over tongue and give creamy mouthfeel
- May form gel when heated
- Removing fat and sugar will drastically change the texture of the products
Why is potassium salt considered an ideal replacer for table salt?
- Member of the same family with sodium in periodic table
- Forms salt with chlorine
- Brings up flavors
- Patients taking heart medicine experience potassium loss
What are the four functions of food additives?
1. Maintain quality/prolong shelf life • Antimicrobial agents: - Salt, sugar - Nitrites - Acids •Antioxidants
2. Enhance sensory characteristics • Color agents - natural and synthetic • Flavor agents - largest group of food additives • Flavor enhancer - salt, MSG •Sweetener
- Control product consistency
•Anticaking agents - calcium silicate, dicalcium phosphate, etc
• Emulsifier - lecithin, mono/diglycerides, etc
• Humectants
• pH control agents - acids, bases, buffers
•Stabilizers and thickeners - Improve/maintain nutritive value
What is the GRAS list?
- Generally Recognized As Safe
- Food additives that have been long used with no health hazards, so exempted from immediate testing
- > 600 of these additives
- All additives will be eventually tested
5 Classes:
Class 1 - Safe
Class 2 - Safe but increased use has to be tested
Class 3 - Future tests have to be done
Class 4 - Guideline has to be provided
Class 5 - To be removed from current list
What are the two roles of nitrates?
- Control botulism in meat
2. Preserve color
What is the risk of using nitrites and how is it currently controlled?
- Form nitrosamines
* Are gradually being phased out
Name the acids used in food products
- acetic
- ascorbic
- citric
- benzoic
- lactic acid
Name the common antioxidants used in food products
- Vitamin C (ascorbic acid)
- Vitamin E (tocopherol)
- Citric acid
- BHA, BHT, and TBHQ
- Sulfite
