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117 Cards in this Set
- Front
- Back
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Why is Water important in foods? |
Universal Solvent Major component of most foods in nat. state Food Quality Processing often removes or alters water in foods |
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Structure of Water |
H2O Tetrahedral Two - Charges (O), Two + charges (H) 104 degrees between H+ atoms, large dipole moment Oxygen atom is highly electronegative |
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Bond energy |
Covalent- 100 kcal/mol Hydrogen- 4-5 kcal/mol |
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Hydrogen Bonding |
3 dimensional, intermolecular hydrogen bonding between 0- and H+ |
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Melting point of water |
High, 0 degrees |
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Boiling point of water |
High, 100 degrees |
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Density of solid form of Water (Ice) |
Low, Ice |
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Specific heat of water (heat capacity) |
High, energy to raise 1 g water 1degree C |
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Special properties of water due to? |
Polarity Large dipole moment Extensive hydrogen bonding |
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Latent heat of water |
high, energy to change state w/out changingtemperature |
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Surface tension of water |
High due to: H-bonding(intermolecularattraction) and weakdispersion forces |
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What decreases surface tension of water? |
increased temperature Emulsifiers |
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What increases surface tension of water? |
Salts and sugars |
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Positive Ionic solute interaction with water |
Orients negative oxygen atom towards solute |
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Negative Ionic solute interaction with water |
Orient positive hydrogen atom towards solute |
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Colligative properties of solutions |
Solution properties that depend on thenumber of particles, not their identity |
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Number of solutes increase |
Boiling point (salt to pasta water) Osmotic Pressure |
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Number of solutes decrease |
Freezing point (salt in ice cream making) Vapor pressure |
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What phase is water usually in? |
Dispersion phase |
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Solutions |
one-phase system containingsolutes with dimensions less than 1 nm (ex.diet pepsi) |
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Colloidal Dispersion |
Containing particlesranging in size from 1-100 nm (ex. milk) |
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Suspension |
Mixture containing solidparticles (> 1 m) that eventually settle (ex.cocoa) |
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Sol liquid dispersion |
Solid dispersed in liquid |
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Emulsion |
liquid dispersed in liquid |
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Foam |
gas dispersed in liquid |
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Free water in foods |
retains physical properties dispersing agent for colloids solvent for salts |
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Adsorbed water in foods |
held tightly (cell walls or proteins) |
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Water of Hydration in foods |
bound chemically (ex. lactose-H2O) |
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Most abundant molecule in foods |
water |
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Water Content in Foods influence |
structure appearance texture taste spoilage chemical reactions nutritional value |
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Determining water content |
Moisture assay: water vs total solids % moisture or g/100g |
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Why measure water content |
Quality factor– Packaging and shipping– Important for Standards of Identity Cheddar cheese < 39% moisture Glucose syrup > 70% total solids Scallops < 82% moisture Economic fraud |
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Specific Gravity |
The weight of a specific volume of substancedivided by the weight of same volume of water.Relative densities. All substances are compared to pure water,which has a specific gravity of 1. |
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Specific Gravity Applications |
indicator of soluble solids content of a foodmaterial:- hydrometer for measuring degrees Brix (solublesugar) in juices, jams, etc. water as floatation device:-separate products based on s.g.-indicates maturity/quality of crops-low density peas are sweeter -salt solution used to separate grades |
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Ice Structure |
Crystalline Each molecule hydrogen bonded with 4other water molecules (not static) 11 structures of ice |
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Only form of ice important in food |
Hexagonal |
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Ice Volume |
Approx. 9% more than liquid water |
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Super Cooling Ice formation |
bringing liquid water temperaturebelow 0C- may reach as low as -10 C- sensible heat removal Ice nucleation |
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Ice Nucleation |
formation ofmany nuclei around suspended particlesor at cell walls. |
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Crystallization |
temperature goes back up toward 0 Cas ice crystals begin to form around nuclei -latent heat removal -phase change from liquid to solid - as water freezes, solutes concentrate inunfrozen water |
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Faster a product is supercooled... |
the more nucleation occurs |
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If product is cooled slowly... |
Few nuclei form crystallization creates fewercrystals, which are large and coarse. |
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Ice effects on quality of food |
When ice crystals are large, cells can rupture, reducing meat,vegetable, and/or fruit textural quality Ice cream becomes coarse (> 50 µm), not creamy |
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Frozen Foods |
Always unfrozen water present Variation in food expansion: – freezer temperature – freezing speed – moisture content – solute concentration |
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Effects of freezing on foods |
Decreases water activity (Aw)– microbial growth– chemical reactions– enzymatic reactions Concentrates solutes in cells– damages proteins– can decrease water holding capacity |
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Freezer Cycling |
Fluctuating Temperatures in freezer Warmer air holds more water vapor thancolder air As temperature changes, water fluctuatesfrom solid to gaseous state Also causes migratory recrystallization infood product as ice crystals melt and thenreform |
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Improper Freezing |
“snow” or ice crystals in package Spreads damage throughout packageduring long-term storage– Enzyme activity Causes “freezer burn” as moisture is lostfrom product Causes water loss during thawing Result: quality loss (texture, color, flavor)and economic loss |
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Moisture Migration during Frozen Storage |
Quality loss (texture, color, flavor) Economic loss (loss of appeal, weight loss) |
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Water activity |
Measure of water accessibility Is water bound or available? Bound water unavailable as a solvent |
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Water Activity Equation |
aw = p/po and ERH/100 • p = partial pressure of water over foodsample at equilibrium • po = vapor pressure of pure water atsame temperature • ERH = equilibrium relative humidity |
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Measuring Water Activity |
Relative humidity sensor Small, enclosed chamber at constant temp Sample reaches equilibrium (no gain or lossof H2O) Relative humidity of headspace is equilibriumrelative humidity aw values between 0 – 1 |
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Water Activity vs. Water Content |
increase in moisture content = increase in water activity Relationship not linear Any ingredient (salt, sugar, …) thatinteracts with water will decrease partialpressure and aw |
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Moisture Content and Activity in various foods |
d |
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Water Sorption Isotherms |
plot of aw or ERH versus moisture content ofsample • usually sigmoidal • unique for each food– chemical composition– physical structure • temperature dependent– ↑ temperature shifts curve to right (higher energy) • steep portion = hygroscopic |
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Adsorption/Desorption Isotherms |
Removing water = desorption– determining dehydration conditions– top curve indicates desorption • Adding water = adsorption– determining hygroscopicity– bottom curve indicates absorption • Curves are not superimposable.– Dehydration/absorption not fully reversible • Shift between curves called hysteresis |
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Hysteresis |
Large shift in some foods (cooked rice)– Not observable in some foods– Depends on: • kind of food • physical changes • amount of water removed • Many theories; no definitive explanation |
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Why does hysteresis matter? |
Can effect whether dehydrated or rehydratedproducts are used in a given application. |
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Water Zone 1 |
Bound water – low aw(< 0.25)– monolayer water; stable; unavailable; notfreezable |
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Water Zone 2 |
Multilayer water – mid aw(~0.25 –0.8)– capillary water– In high moisture food, zone I and zone II < 5%of water |
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Water Zone 3 |
Bulk phase water (~0.8 – 1.0)– “solvent” or “free” water– easily removed by processing– available for microbial growth and enzymeactivity |
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Importance of sorption isotherms |
Indicate awfor food stability • Food drying processes • Packaging materials • Ingredient mixing/compatibility:– different ingredients in a mix (soup mix)– filled products (ex. cream filled donut)– coated products (ex. breaded fish fillet) • Moisture migration driven by aw!!! |
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Effects of Moisture Transfer |
Low moisture flakes– loss of crispness>0.35-0.40• Intermediate moistureraisins– Hardening <0.40-0.45 |
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Effects of Aw on foods |
Influences:– Microbial activity • Bacteria: ~ 0.9 • Yeasts: ~ 0.8 • Fungi: ~ 0.7– Chemical reactions • Enzymatic reactions (stop at ~ 0.3)– Substrate motility • Fat oxidation • Non-enzymatic browning (stop at ~ 0.2) • Hydrolysis (starches, lipids …) |
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By controlling Aw in Foods you can control: |
– Microbial activity – Chemical activity – Safety – Shelf life – Processing characteristics – Quality • texture • nutrition • color/appearance |
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Glassy Solids |
Non-crystalline, amorphous solid • Lack of molecular mobility • Shelf stable • Examples:– Dried pasta – Lollipop – Hardening of dried fruit |
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Glass Transition |
Glassy state Rubbery state • Temperature and moisture dependent • Tg = glass transition temp– Lowest temp at which product exists inliquid/rubbery state • ↑ H20 content = ↓Tg |
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Lipids |
Soluble in nonpolar organic solvents(ether, chloroform, etc.) • Poor solubility in water |
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Simple Lipids |
Neutral fats • esters of fatty acids with glycerol– triacylglycerols, mono and diglycerides • oils and fats • major portion of lipid in foods Waxes • esters of fatty acids with long-chainalcohols• example: cetyl palmitate (cetyl alcohol, 15carbons long) |
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Compound Lipids |
Contain groups in addition to esters of fattyacids and alcohol • Phospholipids:– fatty acids, phosphoric acid, and anothergroup that usually contains nitrogen– phosphatidyl choline (lecithin)phosphatidyl inositol, etc. |
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Derived Lipids |
• Substances derived from neutral lipids orcompound lipids. • Properties of lipids – fatty acids – alcohols (including sterols) – hydrocarbons (carotenoids, squalene..) – vitamins A, D, E, K |
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Fatty Acids |
Hydrocarbon chain • CH3 or methyl group (omega end, ) • COOH or carboxylic acid group (alpha end,) • Unbranched or branched chain fatty acids– branched chain fa’s rare in foods • Most natural fatty acids are even numbered |
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Short Chain FA |
4-10 C |
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Medium Chain FA |
12-14 C |
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Long Chain FA |
> 16 C |
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Chain Length vs. Melting Point |
Greater Length = Greater MP |
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Saturated FA |
Carbons all attached with singlecovalent bonds |
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Palmitic Acid |
16:0 present in almost all natural fats animal depot fats & vegetable oils |
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Lauric Acid |
12:0 widely distributed in nature – seed oils, tropical oils, milk fat |
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Stearic Acid |
18:0 animal depot fat, seed oils, milk fat |
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Ruminant Milk Fats |
Most fatty acids are short and mid-chainsaturated (C4-C18) • Unique in profile of short chain fatty acids,which provide characteristic flavor – butyric acid, 4:0– caproic, 6:0– caprylic, 8:0 • Natural trans fat and branched chain fatsproduced in rumen • Free butyric acid gives rancid butter smell |
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Monounsaturated FA |
One double bond in carbon chain,primarily cis form Humans can make only omega 9and higher |
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Oleic Acid |
18:19 most widely distributed fatty acid, present in allfood fats – liquid at room temperature – main component of vegetable oils – trans form is elaidic acid (in milk andhydrogenated oils) |
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Palmitoleic Acid |
16:17 – minor component in many food fats |
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Polyunsaturated Fats |
Multiple double bonds along hydrocarbonchain, primarily in cis configuration Liquid at room temp. |
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Linoleic Acid |
18:26 essential fatty acid widespread in vegetable oils |
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Linolenic Acid |
18:33 essential fatty acid – widespread in seed oils – seafood, marine oils |
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EPA |
Eicosapentanoic Acid 20:53 aka HUFA (highly unsaturated fattyacid) – Only in seafood, marine oils |
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DHA |
Docosahexanoic Acid 22:63 HUFA – Only in seafood, marine oils |
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Fatty Acid Comp. in Foods |
Genetics– sunflower oil; animals = lean generation pork • Diet– fish and farm animal manipulation • Location of tissue– storage & depot fat = more saturated– membrane lipids/phospholipids = moreunsaturated • Environment– cold = more pufa |
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Iodine Value of fats |
AKA iodine number • Measures degree of unsaturation • Correlates with number of C=C bonds • Grams of iodine absorbed per 100 gsample (g/100g) • unsaturated = iodine absorbed |
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Solid Fat Content |
AKA solid fat index (SFI) • Percent solid fat in a sample in contrast toliquid (non-crystalline) phase • Plotted over a temperature range • Relates to sensory textural attributes, suchas creaminess, waxiness, hardness … • Very important in chocolate! (melt-in-yourmouth characteristics) |
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Saponification Value |
Amount of alkali needed to saponify fat • mg KOH per 1 g fat (mg/g) • Hydrolytic cleavage of fatty acids fromglycerol backbone • An index of mean Mw of triglycerides • Saponification value = fatty acid chainlength of triglyceride |
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Important properties of fats and oils |
Melting point– temperature at which solid fat becomesclear in a capillary tube • Smoke and flash points • Cloud point– temperature at which a cloud is formed ina liquid fat as crystallization begins |
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Nomenclature of Fats |
• Mono, di, and tri-glycerides • Chain length – short fatty acids named first – palmitodistearin not distearopalmitin • Degree of saturation – more saturated fatty acids named first– oleolinoleolinolenin |
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Hydrogenation |
Addition of H2to double bonds ofunsaturated fatty acids • Increases saturation of oils |
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Hydrogenation Purpose |
Purpose: – Improve oxidative stability of oils – Convert liquid oils into hard or plastic fatsfor specific applications |
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Hydrogenation Process |
Occurs in closed vessel under pressure • Add refined oil (water, phospholipids ruincatalyst) • Add H2 gas • Add catalyst (solid nickel, copper, platinum) • Agitate to dissolve gas and mix catalyst • Heat (140-225 C) • Cool, then filter catalyst |
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Hydrogenation nutritional effects |
Essential fatty acidcontent of oils • In partially hydrogenatedfats: many remainingunsaturated fatty acids arechanged to trans - ↓ cardiovascular health - Correlated with ↑ in LDLand ↓ in HDL cholesterol |
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Frying |
Frying conditions:– high heat (~180 - 200 C)– aeration ( O2) • Behavior of food during frying:– water released– oil absorbed (5-40%) |
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Hydrolysis |
Fatty acids cleaved off TG – Caused by high temperature and water – As free fatty acids (FFA) increase, oil becomesmore acidic– ↑ hydrolysis = ↑ “acid value” |
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Oxidation |
Hydroperoxides, aldehydes, and furtherdecomposition products |
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Polymerization |
TAG products form dimers and oligomers – Solid, sticky, residue |
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Frying Oil Deterioration |
Free fatty acids increase • Oil color darkens • Iodine value decreases • Foaming increases • Viscosity increases • Nutritional value decreases • Sensory quality decreases • Sticky residue formed • Smoke point decreases |
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Decomposition of oil affected by |
Temperature – Turnover rate – Frying time – Metal contaminants – Antioxidants – Moisture content of food – Fatty acid composition of oil – Filtration |
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Interesterification |
Rearranging fatty acids among triglyceridesor within triglycerides • Ester exchange between OH positions • Chemical or enzymatic process • Can be random or directed • Modify crystallization behavior and physicalproperties of fats • Can produce solid fats for margarine andshortening low in trans fats • PUFAs not destroyed |
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Process of Interesterification |
Occurs in closed vessel under pressure • Add specific oils– ex) react canola oil with palm oil • Add catalyst (sodium methoxide) • For directed interesterification, changetemperature– above or below melting point of fatty acids ofinterest– some fatty acids will precipitate and some willremain liquid and undergo reaction |
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Shortening Production |
Properties of lard • disaturated TGs • Forms coarse crystals even when rapidlysolidified (causes poor baking quality). • Interesterification:– modifies fatty acid position and lard quality.– can produce fat with higher solids content athigher temps. |
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Fat Crystal Polymorphism |
Most fats crystals have at least 3 basicpolymorphs:– α (alpha),’ (beta prime), (beta) • Different polymorphs have different shapesand melting points, and strongly influenceproduct quality • α ’ (transformation or “ripening”) |
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Tempering Fats |
Heating and then rapidly cooling torecrystallize fats • Increases nucleation, decreases crystal size • Changes melting temperature, solid fatcontent, and texture • Used for:– reducing coarseness– increasing creamy texture– producing specific polymorphs for differentapplications (e.g. cocoa butter in chocolate) |
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Cocoa Butter Polymorphism |
Six polymorphs: I – VI • I = lowest mp; VI = highest mp• Polymorph from controlled by regulatingprocessing temperatures • V is best form for chocolate:– Best snap at room temperature– Stable gloss– Smooth and rapid melt in mouth– Best flavor release– Stable, low energy form |
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Refining Oils |
Starting with crude oil or fat:– Pressed olive oil– Cold expelled soybean oil– Crude fish oil– Fat trimmings from pigs, other animals • Remove:– Free fatty acids– Phospholipids– Carbohydrates– Proteins– Water– Pigments |
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Settling |
heat oil and let stand: aqueous phase separates, and waterand water soluble materials can be removed |
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Degumming |
use dilute acid to produce a “gum” containing phospholipids |
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Neutralizing |
Use alkali to remove free fatty acids (as soaps) |
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Blanching |
heat and treat w/adsorbents to remove pigments(bentonite, fullers earth, activated charcoal) |
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Deodorization |
steam distillation: removes volatile oxidized lipids andflavors |
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Winterizing |
Making oil less cloudy at refrigeratortemperatures • Separating out high melting point TGs(fractionation) – Cool oils to set temperature. High melting pointtriglycerides will crystallize. – Filter out or centrifuge out solid fatty acids. |
