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146 Cards in this Set
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Define lipid |
any food compound soluble in non-polar organic solvent (diethyl ether, petroleum ether, chloroform) |
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What are the three classes of lipids? |
1. Simple 2. Compound 3. Derived lipids |
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What are the simple lipids? |
MAJOR CATEGORY Fats, glycerides, waxes Examples: triglyceride, diglyceride, long chain alcohol FAs |
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What are the compound lipids? |
Phospholipids, sphingomyelins, cerebrosides Examples: FAs with phosphoric acid and other groups, inositol, choline |
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What are the derived lipids? |
General catch all term, includes many Examples: sterols (cholesterol), phytosterols (stigmasterol), synthetic modified sucrose polyester (Olestra) |
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What are the components of fatty acids? |
1. Acid group (COOH) 2. Hydrocarbon tail (varies, determines the acid) |
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What is a saturated FA? |
saturated with hydrogens no double bonds mostly straight chain, may be branched |
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What is an unsaturated FA? |
includes at least one double bond monounsaturated = 1 double bond polyunsaturated > 1 double bond can be in cis or trans configuration |
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Give the alkane, sytematic name, and common name for a saturated FA with 4 carbons |
Butane Butanoic Acid Butyric |
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Give the alkane, sytematic name, and common name for a saturated FA with 12 carbons |
dodecane dodecanoic acid Lauric |
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Give the alkane, sytematic name, and common name for a saturated FA with 14 carbons |
Tetradecane Tetradecanoic Acid Myristic |
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Give the alkane, sytematic name, and common name for a saturated FA with 16 carbons |
Hexadecane Hexadecanoic Acid Palmitic |
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Give the alkane, sytematic name, and common name for a saturated FA with 18 carbons |
Octadecane Octadecanoic Acid Stearic |
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When are branched saturated FA observed? |
uncommon seen in bovine milk ex: 3-methyl butanoic acid |
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How are FAs named using delta naming? omega? |
count from carbonyl carbon as #1 as opposed to omega system where terminal carbon is #1 |
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Common name for 14:1 (9) |
Myristoleic Has double bond at position 9 (delta) |
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What is a conjugated FA? |
methylene group will commonly separate the double bonds (these are NOT conjugated) Conjugated = ...CH2-CH=CH-CH=CH-CH2... |
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Common name for 18:1 (omega 9) |
Oleic |
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Common name for 18:2 (omega 6) |
Linoleic |
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Common name for 6:0 |
Caproic |
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Common name for 8:0 |
Caprylic |
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Common name for 10:0 |
Capric |
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Common name for 20:0 |
Arachidic |
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Common name for 16:1 |
Palmitoleic |
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Common name for 18:3 |
Linolenic |
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Common name for 20:4 |
Arachidonic |
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Common name for 22:5 |
Docosapentaenoic |
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Describe an ester bond |
Bond between acid and alcohol (glycerol) RCOOH + ROH --> RCOOR + H20 |
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What makes up a triglyceride? |
Glycerol 3 FAs |
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What makes up a phospholipid? |
Triglyceride Phosphoric Acid |
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What are sterols? |
Lipids that make cell membranes less permeable to small molecules (fill in gaps) In animals: cholesterol In plants: phytosterols |
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Name the plant sterols |
Phytosterols: Sitosterol (major) Stigmasterol Cholesterol (trace) |
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What are the nutraceutical products Benecol and Take Control rich in? |
Stigmastanol (sitosterol) Lowers blood cholesterol and decreases risk of heart disease |
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Characteristics of milk fat |
Short chain saturated (C4-C12) Branched, trans |
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Characteristics of lauric acid fat |
Coconut fat Palm kernel rich in lauric acid (12:0) 40-50% and myristic acid |
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Characteristics of vegetable butters |
Palm oil Cocoa butter high ratio of saturated solid at RT |
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Characteristics of oleic/linoleic oils |
Most vegetable oils corn cottonseed peanut sunflower olive sesame |
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Characteristics of linolenic oils |
up to 10% linolenic acid soybean canola wheat germ walnut (flax/linseed >50%) |
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Characteristics of animal fats |
high in saturated fat |
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Characteristics of marine oils |
high amount of long chain polyunsaturated omega 3 FA in cold water fishes very unstable |
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What are the properties of Olestra (Olean) |
Same functionality of tryiglycerides with no calories Large bulky sucrose molecule inhibits action of lipase enzymes on ester bonds Heat stable Approved in chips, crackers, popcorn |
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What are the problems with Olestra? |
intestinal distress with moderate consumption loss of carotenoids suspected cancer risk |
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Describe the chemistry of Olestra |
Sucrose polyester FA attached to the OH groups of sucrose 6-8 OHs are esterified Can use different FA to achieve functional properties |
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What is Caprenin? |
A modified lipid that has reduced calories (5 kcal/g) Similar functionally to cocoa butter Applications: soft candy, confection coatings Problems with choc bloom |
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What is caprenin made from? |
rapeseed or peanut oil AND coconut or palm kernel oil FAs: Capric (10:0) Caprylic (8:0) Behenic (22:0) |
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What is Salatrim? |
Brand name Benefat Modified fat with reduced calories (5kcal/g) short and long acyl triglyceride molecule Similar to caprenin Same functionality as cocoa butter (confection) |
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What soybean modification is currently in development? |
produces 20% stearidonic acid (18:4 omega 3) metabolized to EPA Omega 3 without fish oil! (18:3 alpha linolenic in flax is metabolized to EPA at very low conversion) |
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Where are trans found? |
UNCOMMON ruminants hydrogenated oils (margarine, shortening) |
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Functional difference between cis and trans |
trans have much higher melting temp (solid) |
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Why do trans have higher melting point? |
hydrocarbon tails pack tightly behave more like saturated FA |
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How are trans FA defined for labeling? |
>1 isolated trans bond conjugated do not count (CLA) Does not count fully hydrogenated FA (trace PHO) |
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What is low-linolenic soybean/canola |
soy normally 7-10% linolenic modified > 1-3% Why? substitute for PHO in frying very stable oil, requires less hydrogention better flavor performance, less oxidation no increase in saturated fat |
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Concerns with palm oil |
Sustainability (culprit for deforestation) |
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Define autoxidation |
Reaction of O2 with organic cmpds causing addition of oxygen and subsequent decomposition Problem for lipids with CC double bonds |
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Three stages of autoxidation process |
1. Initiation 2. Propagation (self perpetuating, hence AUTOoxidation) 3. Termination |
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Stages of free radical process |
UNSATURATED MOLECULE Reacts with pro-oxidant to produce FREE RADICAL reacts with oxygen to produce HYDROPEROXIDE further reacts to produce BREAKDOWN PRODUCTS, RANCID OFF FLAVORS |
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Describe the initiation step of autoxidation |
H is extacted from the lipid (FA, ect) Homolytic cleavage produces free radical Extracted H is next to double bond (a-H) RH --> R* + H - X |
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Describe the propagation step of autoxidation |
O2 reacts with free radical to produce a peroxy-free radical that can abstract an a-H R* + O2 --> ROO* ROO* + R'H --> ROOH + R'* |
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Describe the termination step of autoxidation |
R* + 'R* --> R'R --> polymerization (not volatile) R* + 'ROO* --> R00'R --> volatile products |
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What are the important autoxidation breakdown products? |
ALDEHYDES also alcohols, ketones |
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What is A cleavage and B cleavage? |
A cleavage - next to double bond, produces aldehydes, alkenes B cleavage - furthest away from double bond, produces shorter chain FA, alkenals that further oxidize at a-H |
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What factors influence autoxidation? |
1. FA comp (more unsat, more AO) 2. Free FA 3. O2 conc and SA 4. temperature 5. light, active O2 6. Presence of pro-oxidants (Fe, Cu, heavy metal) 7. Presence of antioxidants |
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List tests for oxidation |
1. Peroxide value 2. Direct analysis of end-products 3. TBA or TBARS 4. Sensory 5. Free FA 6. Polar compounds 7. Electronic nose |
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Describe peroxide value |
Titrate with iodine to blear end point Only works in early stage 5-20 meg O2/kg is acceptable ROOH + KI >> I2 + starch + Na thiosulfate |
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Describe how you would analyze end products for oxidation |
look at aldehydes, ketones produced Often use GC or GC-MS (headspace analysis) |
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Describe the TBA / TBARS test |
TBA = thiobarbituric acid test TBARS = thiobarbituric acid reactive substances works best for linolenic acid values specific for food type reagent + aldehyde + acid + heat --> red color |
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Describe the Active Oxygen Method or Swift Stability Test |
Used to determine lipid stability Bubble O2 through heated sample and monitor peroxide value OR measure conductivity |
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FDA/USDA regulation regarding synthetic antioxidants |
0.01% allowed as % of total fat 0.02% allowed in any combination |
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Four requirements for antioxidants |
1. nontoxic 2. active at low concentrations 3. lipophilic 4. stable under processing conditions (carry through) |
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List 5 types of antioxidants |
1. phenolics 2. tocopherols 3. carotenoids 4. chelators 5. reducing agents |
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Phenolics |
synthetic and natural versions scavenge free radicals naturally occurring in rosemary, thyme, sage, grapes, fruits |
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Tocopherols |
Scavenge free radicals alpha-tocopherol (vitamin E) in oils important as natural source |
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Carotenoids |
example: beta carotene inhibit singlet oxygen formation |
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chelators |
examples: EDTA, citrate tie up metal pro-oxidants not technically an antioxidant |
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reducing agents |
example: ascorbate, erythorbate, ascorbyl palmitate electron donors reducing agent is oxidized instead of lipid |
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Synthetic phenolic antioxidants |
PG: propyl gallate BHT: t-butylated hydroxy toluene BHA: t-butylated hydroxy anisole TBHQ: t-butylated hydroquinone All have: phenyl group >1 hydroxyl group |
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How do synthetic phenolic antioxidants work? |
Stops propagation Regenerates antioxidant activity Antioxidant will be gone, but free radical is removed |
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How is rendering accomplished? |
grind oil/fat material warm with water or steam or dry either be open kettle (meaty flavor) or closed kettle (low heat and vacuum) |
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When is cold press used? |
high oil seeds sesame olive (extra virgin) |
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When is hot press used? |
More efficient than cold press red palm |
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When is solvent extraction used? |
Most common neutrally-flavored oils uses hexane (non-polar light petroleum) with pressing soybean peanut corn palm oat very efficient, good quality oil |
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What products are removed during refining? |
free FA phospholipids waxes pigments autoxidation products |
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Settling and Degumming |
Removed phospholipids, CHO, water using steam, then cool and separate water soluble materials Add water, heat, agitate, settle, filter/centrifuge |
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Alkali treatment |
removes free FA as their oil-insoluble salts (foots) NaOH+FFA --> Na + Salts, add water and remove |
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Bleaching |
Reduces color (chlorophyll, carotenoids, xanthophylls) Uses bleaching clay adsorbents (Al-silicate, bentonite) |
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Deodorization |
removed volatile flavor compounds using vacuum and steam injection cottonseed, coconut used as final clean up to remove aldehydes Final peroxidase value should be close to 0 |
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Hydrogenation |
converts oils to solid, plastic fats by saturated with H As of 2018 must have iodine value <4 |
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Selective hydrogenation |
H added to most unsat FA containing active methylene groups of oil produces PHOs (obsolete in 2018) Used in lard, margarines |
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Interesterification |
redistribute FA on glycerol which modifies crystallization behavior and physical properties Produce uniform texture and melting Used to make modified fats (caprenin, salatrim) |
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Winterization |
use low temps to solidify and remove higher MP saturated glyceride "stearines" from oil cottonseed |
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Active compound in olive oil |
oleocanthal has the same pharmacological activity as ibuprofen |
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Describe thermal oxidation |
heat accelerates oxidation process same initial mechanism as autoxidation occurs the most when the oil is hot and no food is being fried reactions are more complex than those at RT |
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Deep frying hydrolysis |
Water on surface of food evaporates in contact with hot oil water flows from interior to exterior "pumping" steam indicates pumping is occurring hydrolysis occurs at glycerin blackbone |
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Products of frying oil hydrolysis |
partial hydrolysis: FFA + diglyceride FFA + monoglyceride complete hydrolysis: FFA + glycerin |
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Effect of hydrolysis on frying oil |
FFA more volatile than glycerides they cause the smoke point to decrease acidic material will further break down the oil |
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Deep frying oxidation |
produces: polar compounds, polymers, volatiles combine to form varnish darken the oil |
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Four methods to test frying oil |
peroxide value FFA Total polar components Color (Lovibond, Gardner Red Color) |
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Peroxide value |
measures oxidative state of unused oil higher value = more oxidized |
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FFA |
test strips or titration determines the amount in oil |
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Total polar components |
chromatography or capacity instrument some countries limit 27% |
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Capacitive measurement |
measures total polar materials based on dielectric constant gives %polar/TPM |
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What phenomenon does lipid polymorphism explain? |
fats with identical structures having different melting temperatures |
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List three basic types of lipid polymorphism |
1. alpha - low melt, less stable, little structure 2. beta' (loose chair) - med melt, med density 3. beta (tight chair) - high melt, high density |
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Define suspension/foam/emulsion |
suspension: solids dispersed in liquid foam: gas dispersed in liquid emulsion: liquid dispersed in liquid (oil/water) |
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What is required to create an emulsion? |
energy! work = suface tension x surface area |
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What two action occur that destroy an emulsion? |
flocculation: droplets gather together coalescence: droplets break and merge together |
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What is HLB? |
hydrophilic lipophilic balance High HLB = very polar Low HLB = very low polarity |
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Application of low HLB (3-6) |
w/o emulsifier |
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Application of med HLB (8-18) |
o/w emulsifier |
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Application of high HLB (13-15) |
detergent |
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Examples of synthetic emulsifiers |
Tweens (o/w emulsion) - polyoxyethylene sorbitol monooleate Spans (w/o emulsion) - sorbitan monostearate |
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What is a surfactant? |
molecules that lower surface tension (amphiphilic) has hydrophilic/polar and hydrophobic portions |
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List three lipid surfactants |
1. fatty acids 2. phospholipids 3. monoglycerides/diglycerides |
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Name a macromolecular surfactant |
protein alpha-lactalbumin |
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Protein function |
Structure (muscle, movement) Carriers (hemoglobin, lipoprotein, ferritin) Messengers (hormones, insulin, GH) Nutrition (casein) |
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What makes proteins functionally unique from CHO gums? |
Heat set ability Gelatin heat set is reversible |
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Basic structure of AA |
(basic) H3N - CRH - COO (acidic) |
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Types of R groups |
1. nonpolar/hydrophobic ex: valine CH(CH3)2 2. uncharged polar/hydrophilic ex: serine CH2OH 3. acidic/neg charge ex: aspartic CH2COO 4. basic/pos charge ex: lysine (CH2)4NH3 |
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Peptide bond |
strong bond with partial double bond character COO + NH3 --> CONH |
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Where does h-bonding occur in beta pleated sheets? |
between CO and NH - peptide bonds line up either parallel or antiparallel |
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What forces stabilize tertiary structure? |
weak forces disulfide bonds |
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Disulfide bonds |
covalent bond between two cysteine residues to form cystine strong, but susceptible to redox stabilize tertiary structure to make proteins resistant to heat |
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Hydrophobic interactions |
van der Waals - weak, dipole, seen with nonpolar AA, seen on interior of molecules |
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Hydrogen bonding |
weak forces between H and electronegative O cumulative effects can be significant |
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Electrostatic bonds |
interactions between charged groups not common divalent cation bridges seen with very acidic proteins (same as low DS pectin) |
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Ninhydrin test |
reacts with free amine group to produce a color - measure with spectrophotometer |
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Biuret method |
not suitable for entire food matrix, only isolated fractions works when two or more peptide bonds are present protein reacts with copper sulfate in the presence of NaOH to produce a purple color |
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protein solubility - pH |
isoelectric precipitation occurs when protein at isolectric point has net charge reduced proteins become attracted to eachother and precipitate out of solution |
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protein solubility - salt |
above 1.5 M salt, proteins will "salt out" |
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protein solubility - nonaqueous solvent |
alcohols, ketone, organics decreases polarity of solution proteins interact and precipitate |
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Physical agents that denature proteins |
heat mechanical action freezing |
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Chemical agents that denature proteins |
acids/alkali organic solvent urea detergent (SDS) |
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Differences in denatured proteins |
decreased solubility decreased water binding loss of biological activity increased protease susceptibility increased viscosity formation/relocation of disulfide bridges |
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Describe Maillard browning process |
amino-containing compounds react with reducing sugar above pH 6 at high temperature |
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Three stages of Maillard browning |
1. initial - no color (addition reaction) 2. intermediate - colorless, some at UV range (sugar dehydration, forms reductones, melanoidins) 3. final stage - highly colored vis and UV (malanoidin/imine pigments formed) |
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What is Strecker degradation? |
reaction of AA with reductone to form pyrazines Responsible for flavor and aroma destroys AAs |
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Describe the sugar-amine condensation step of Maillard browning |
Reducing sugar reacts with AA/peptide w/N-terminal to produce 1-amino-2-keto sugar and water |
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Products of Maillard browning |
Pigments (brown) - caramel color Aldehydes - reductones, dicarbonyls Pyrazines - desirable flavor Sugar - HMF, aroma Hating - butter, meat flavor |
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How to control Maillard browning |
temperature - lower = less browning pH = does not occur <6 aW = does not occur <0.2 Remove metal ion Remove sugar sulfites can inhibit |
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Reaction steps involved in acrylamide production |
Asparagine reacts with sugar at high temp in presence of reducing sugar |
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Major protein in milk |
casein (80% of milk protein) Precipitates with acid <4.6 or enzyme (rennin/chymosin) Precipitates to paracasein (soluble if Ca is removed) |
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Minor protein in milk |
Whey protein b-lactoglobulin, a-lactalbumin, blood protein Soluble at low pH Ppt with heat |
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Muscle protein |
sarcoplasmic protein (enzyme, myoglobin) myosin actin soluble in 2-3% salt troponin/tropomyosin |
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Connective tissue protein |
Stroma Gives toughness Collagen (insoluble) heat to form gelatin Elastin |
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Protein in eggs |
ovalbumin conalbumin ovomucoid lysozyme avidin flavoprotein yolk - lipoprotein dispersions |
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Soy protein |
all essential AAs 20% albumin 80% globulin ppt <4.5 pH flour 50% protein concentrate 70% protein, defatted isolate 90% protein |
