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131 Cards in this Set
- Front
- Back
Functional Properties |
Physiochemical properties thatenable proteins to contribute to thedesirable characteristics of food. |
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Functional roles of protein in soups, sauces |
emulsification, water retention |
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Egg substitutes |
Foaming, gelation |
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Dairy |
emulsification, coagulation |
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Sausages |
emulsification, water retention |
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Bread |
dough formation, browning |
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Cool Whip |
Foaming |
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Three Main Categories of protein functionality |
1. Hydration properties – protein-water interactions 2. Protein-protein interactions 3. Surface properties |
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Are main categories independent of each other? |
• Categories not independent of each other – Gelation: protein-protein and protein-waterinteractions – Solubility: protein-protein and protein-waterinteractions |
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Hydration properties of proteins |
Includes the following properties: – Water absorption/retention – Swelling – Solubility – Viscosity |
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Hydration influenced by: |
– Surface amino acids/amino acid comp. – Protein concentration • ^ Protein concentration = ^ water absorption– pH • change in pH = change in protein ionization (net charge) • at the pI of a protein: – maximal protein-protein interactions – minimal protein-water interactions » ex) beef post-rigor » ex) production of soy protein isolate |
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Hydration also influenced by: |
– Ionic Strength • Low salt ( < 1M) = ^ solubility (“salting in”) • High salt = decreased solubility (“salting out”)–Temperature • Extreme ^ Temp = dec, solubility • Extreme ^ Temp = dec. water binding • Extreme ^ Temp = dec. hydrogen bondingbetween protein and water • Ex) cooked meat– ^ Aggregation (denaturation) = dec. surface area |
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Pro-pro Interactions |
– Aggregation & precipitation – Gelation properties |
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Gelation |
– Denatured molecules aggregate through variousbonds to form a 3D protein network – Hydrogen bonding, disulfide bonds, hydrophobicinteractions, ionic bonds – Large amounts of water (98%) can beentrapped in protein matrix |
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Gelation examples |
• Tofu • Bread dough (gluten,disulfide bridges) • Gelatin gels • Yogurt • Surimi gels |
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Gelation Processes |
• Heat induced gelation • Acid coagulation • Enzyme action |
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Surimi protein gels |
• Mixture of fishprotein, water, andsalt • Mixture is heated,then cooled indifferent moldshapes, or spuninto protein fibersand shaped |
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Types of protein gels |
Thermally reversible Thermally irreversible |
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Thermally irreversible gels |
– “Thermoset” – Myosin gels (surimi), ovalbumin gels (cookedegg whites, custard) – More disulfide bridges – Turbid, opaque, and transparent gels |
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Thermally reversible gels |
– “Thermoplastic” – Gelatin (collagen) – Hydrogen bonding forms junction zones – Can melt and reform gel |
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Surface properties of proteins |
• Proteins act at surfaces between phases • Includes the following: – Emulsification properties • oil and aqueous phases – Foaming properties • gas emulsions |
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Emulsification properties |
• Formation and stabilization of emulsions • Proteins migrate to and adsorb at interfacebetween oil and aqueous phase • Proteins act as surfactants |
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Factors that influence a protein’s ability to act as emulsifier: |
• Amphiphilic structure • Solubility (migrate to interface) • Partial unfolding (flexibility) |
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Flexible protein at an interface |
• Loops andtail in aqueousphase • More trains = dec. interfacialtension |
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Emulsification properties influenced by |
pH of solution or food matrix protein solubility |
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pH of solution or food matrix |
• Effects solubility and aggregation • Effects shape of protein (denaturation) |
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Protein solubility |
• ^ Protein solubility = ^ emulsion stability(Proteins dissolve and migrate to surfaces) • Any factor that influences solubility will influenceemulsification properties |
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Emulsification properties |
• Emulsion stability – how long does emulsion last? – use graduated cylinder, and follow phaseseparation • Emulsion capacity – amount of oil that can be emulsified – continue adding oil and homogenizinguntil viscosity decreases |
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Examples of emulsification |
• Salami, a meatemulsion • Emulsion ofprotein and fat • Salt is added tosolubilizemyofibrillarprotein |
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Foams |
gas emulsions Dispersions of gas bubbles in continuous liquidor semisolid phase |
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Gas |
typically air or CO2 |
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Formation of foam |
– Formed by whipping or beating aqueous proteinsolution in presence of bulk gas phase – Or, by sparging: bubble gas into aqueoussolution of low protein concentration – A gas emulsion forms, and the true foamseparates – Thin liquid (or semi-solid film) layers separate gasbubbles |
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Proteins and foam formation |
– Proteins act as soluble surfactant to decreasesurface tension of continuous phase – If proteins completely denatured, then ineffective |
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Good foaming proteins |
• high rate of diffusion • ability to unfold at interface • ability to form a stable film around gas bubble |
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Foam Stabilizer additives |
– Increase viscosity of liquid phase • Sucrose, gums, polyols • Addition of insoluble solids such as flour,starch – Acids increase denaturation • Cream of tartar • Lemon juice • Vinegar |
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Other functions of proteins |
• Texturization – Texturized proteins(soy flour, wheatgluten) – Films, fiberformation (meatsubstitutes) • Coloring: – Myoglobin: meatcolor – Maillard browning |
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Why modify functional properties? |
– To improve functional properties of proteins forspecific applications • Chemical, enzymatic, and physical methods |
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How do you modify functional properties |
– Crosslinking (chemical or enzymatic) • inter- or intramolecular crosslinking – Hydrolysis – Adding new groups (fatty acids, succinic acid,phosphate, carbohydrates) – Deamidation (eg. Glutamine glutamic acid) |
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Carbohydrates |
• Major energy source for world population • >70% world caloric intake • Abundant, widely available, inexpensive • Primarily provided by plants • Common component of food: natural andas added ingredients • Many forms: sugars, starches, fibers, gums, … |
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CHO provide foods with: |
– Bulk – Structure – Viscosity – Stability (emulsions & foams) – Water holding capacity – Browning – Flavors & aromas |
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Monosaccharides |
•“simple sugars” • cannot be hydrolyzed • occur naturally in small amounts • Polyhydroxylated aldehydes or ketones • Hydrophilic OH groups = soluble in water • Decompose easily from heating (losewater) |
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Most important monosaccharides |
Hexoses – Glucose: small amounts (aka dextrose) – Fructose: “Fruit sugar” – Galactose: not present in “free” form – Mannose (another glucose isomer) |
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Oligosaccharides |
• disaccharides, trisaccharides …. • can be hydrolyzed • 10 > monosaccharide units |
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Polysaccharides |
• Large # of monosaccharide units • Starch = 100-2,000 monosaccharide units |
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Monosacch Isomerization |
• Same formula, different structure • C6H12O6 • Catalyzed by base or enzyme • Ex) glucose isomerase convertsglucose to fructose to produce highfructose corn syrup |
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Monosacch ring formation |
• Carbonyl group reacts with own alcoholgroups to form a hemiacetal or hemiketal: – 5-membered furanose ring – 6-membered pyranose ring (more stable) • Hemiacetal/hemiketal: – Carbon bonded to OH group and ORgroup – Ring conformation open chain |
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Solubility influenced by: |
– Structure: fructose and sucrose mostsoluble – Purity: Mixed sugars have higher solubility – Temperature: Higher temp increasessolubility– Mechanical energy: Increases solubility |
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Other monosacch |
• Sugar alcohols • Glyconic acids • Glycuronic acids |
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Sugar Alcohols |
• No carbonyl group, each carbon ishydroxylated • Occur naturally in some fruits– Pears (sorbitol), celery (mannitol),strawberries (xylitol) • Produced by hydrogenation (reduced):– Glucose + H2 = sorbitol– Xylose + H2 = xylitol • Poorly absorbed in intestine • Nonfermentable • Sugar free chewing gum, mints, etc. |
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Glyconic Acids |
• Glyconic acids: oxidizedsugars with a carboxyl groupat carbon #1 • Glucose → Gluconic acid • Mannose → Mannonic acid • Galactose → Galatonic acid– Gluconic acid • fruit, honey, wine • food additive : leavening agent,acidifier |
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Glycuronic acids |
• Oxidized sugars with acarboxyl group at highestnumbered carbon • Glucose → Glucuronic acid • Mannose → Mannuronic acid • Galactose → Galacturonicacid • Important constituent of manygums |
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Reducing Sugars |
• Any sugar with a free hemiacetal group • H is given up from the *OH group, and thesugar becomes oxidized • Reducing sugars can reduce metal ions– Cu2+ → Cu+ (color change from blue to redbrown:“sugar stick” tests)– Ag+ → Ag0 |
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Importance of reducing sugars |
non-enzymatic browning |
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Reducing sugars include |
glucose, fructose, mannose,maltose, etc., but not sucrose |
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Disaccharides |
• Two monosaccharide units linked by aglycosidic bond • Condensation reaction with loss of 1water molecule – Anomeric carbon on the hemiacetalreacts with alcohol to form acetal – Acetals have a carbon bonded to two -OR groups • Carbohydrate acetals = glycosides |
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Disaccharide properties |
• Homogeneous or heterogeneous • Stable in water • Can be hydrolyzed:– Acid, heat, or enzymes |
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Lactose |
glucose hemiacetal +galactose – Beta 1, 4 glycosidic bond – Milk sugar – Reducing sugar |
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Maltose |
glucose + glucose – Alpha 1, 4 glycosidic bond – Malt sugar, corn syrup – Reducing sugar |
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Sucrose |
glucose + fructose – Alpha 1, 2 glycosidic bond – Table sugar, beet sugar,cane sugar – Non-reducing sugar |
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Sugar Reactions |
Caramelization Invert sugar |
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Caramelization |
– A type of non-enzymatic browning – Sucrose or corn syrup typically used – High temperatures required (thermolysis) • > 160 C |
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Complex set of reactions for caramelization |
– Complex set of reactions: • Dehydration of sugar molecule • Formation of double bonds – Conjugated double bonds produce color • Molecules polymerize • Hundreds of products are formed |
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Caramelization products |
– Melanoidin pigments, bitterflavors, & aromatic compoundsare formed – Products are used as colorantsin food industry• Soft drinks, beer, soy sauce,caramel candies, gravy, bakedgoods, dry seasoning powders |
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Invert Sugar |
– Syrup or liquid – Produced by sucrosehydrolysis – Use enzyme (invertase) oracid (tartaric, citric, ..) – Produces mixture of glucoseand fructose – Partially or completelyhydrolyzed |
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Invert Sugar properties and uses |
– Sweeter taste – Lower freezing point – Acts as humectant • Hygroscopic: keeps products moist – Sweetener in beverages – Used in confectionery industry: • Prevents crystallization ofsugar in icings, fondants,jellies and jams |
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Sweetness of sugars |
• Fructose: 150 • Sucrose: 100 • Xylitol: 95 • Glucose: 74 • Sorbitol: 54 • Galactose: 48 • Maltose: 46 • Lactose: 39 |
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Sucralose |
• Synthesized from sucrose • Three OH groups selectivelysubstituted with chlorine • 600x sweeter than sucrose • Non-metabolizable, non caloric • Heat and acid stable • Produced in 1976, FDA approvalin 1998 • AKA Splenda: contains dextrose,maltodextrin, sucralose |
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Other important oligosaccharides |
• Raffinose– 3 units: glucose + fructose + 1 galactose • Stachyose– 4 units: glucose + fructose + 2 galactose • “Galactosides” • Soybean and other legumes • Not hydrolyzed, non-digestible • Antinutritional factor: flatulence – Processing methods can decrease levels |
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Cyclodextrins (Schardinger sugars) |
• Cyclic, non-reducing oligomer • Glucose subunits: (6), (7) and γ (8) • Alpha 1,4 linkages • Donut shape with central hydrophobiccore |
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Cyclodextrins Properties |
• Good binding properties incentral hydrophobic portion – Masks bitter or unwanted flavors – Can remove caffeine andcholesterol • Good flavor carrier and stabilizer • Protects vitamins, PUFAs, andcolors • Produced from hydrolyzedstarch using cyclodextringlucotransferase |
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Maillard Browning |
Non-enzymatic browning Thermal processing and storage Foods containing protein and reducingcarbohydrates (or other carbonylcompounds) |
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Changes in maillard browning |
Results in flavor, aroma, and colordevelopment |
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Desirable Effects |
Browning of bread crust Chocolate flavor: roasting of cocoa beans “Meaty” flavor and color production inroasted meats Coffee flavor: roasting of coffee beans |
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Undesirable effects |
Brown discoloration in french fries and potato chips in frying Discoloration of dried milk Discoloration and unwanted flavors indried egg Decrease in protein quality |
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Reaction process |
Glycosylamine formation Formation of amadori product Complex of intermediate rxns Formation of melanoidins or volatilecompounds |
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Glcosylamine formation |
- condensation reaction between a nonionizedamino group and carbonyl ofopen chain reducing sugar - the free amino group on a free aminoacid, an amino acid R-group, or theterminal alpha-NH2 of a protein - reversible step - non-stable intermediary product |
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Formation of amadori product |
- rearrangement of glycosylamine - stable products formed: ketosamine andaldosamine - non-reversible |
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Complex of Intermediate rxns |
- Aldosamine and ketosamine -> -> carbonyl derivatives and othercompounds |
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Formation of melanoidins or volatile compounds |
- a series of degradation andcondensation reactions - melanoidin pigments formed: - brown nitrogenous compounds - contain pyrazine and imidazole rings - contain HMF (5-hydroxymethyl furfural) |
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Factors that influence reaction rate |
Temp. metal ions Conc. of reactants Water activity pH Type of sugar Amino Acid |
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Temperature |
– ^ Temperature = ^ browning – cooking, evaporation, drying,pasteurization, condensation |
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Metal Ions |
– Iron and copper catalyze reaction |
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Concentration of reactants |
– ^ concentration = ^ browning |
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Water Activity |
– From 0.2 to 0.8: • ^ water activity = ^ browning – Over 0.8: • excess moisture inhibits (negative feedback) |
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pH |
– decreased pH = decreased browning– due to ^ protonation of amine |
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Type of sugar |
– reducing sugar (open chain) – monosaccharides > disaccharides |
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Amino Acid |
– Lysine very reactive (due to extra epsilon amine group) • significant loss of essential amino acid lysine – proline, arginine, asparagine |
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Inhibition |
• Decrease water activity • Reduce processing and storagetemperatures • Acidify product • Modify sugar composition – Change formulations – Add glucose oxidase to dried eggs • Addition of sulfur dioxide / bisulfites – prevents condensation into melanoidins • Does not prevent lysine loss – also reacts w/thiamine |
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Acrylamide |
• Fried, roasted or bakedfoods • Maillard browning • Reaction betweenasparagine and reducingsugars or other reactivecarbonyls • Temperatures > 120C |
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Acrylamide dosing |
• Levels increase with intensity and duration ofthermal processing. • Cancer in rats when administered orally inhigh dose experiments. |
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Asparaginase |
– added to bread or potato mixtures – reduces acrylamide formation during thermalprocessing. |
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Hydrocolloid Sources |
• Plant seeds: guar, locust bean • Plant exudates: gum arabic, ghatti,tragacanth • Seaweeds: agar, carrageenan, alginate • Microorganisms: xanthan, gellan gum |
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Manufacturers |
TIC Gums FMC Biopolymer Cargill |
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Functions of Hydrocolloids in foods |
• Viscosity • Gelling • Suspension • Emulsion & foam stabilization • Encapsulation • Film forming • Water binding & management • Fat replacement • Dietary fiber |
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Gum Properties |
• Hydrophilic polysaccharides • Provide viscosity at low concentrations ( < 1%) • Linear or branched molecules • Polymers can be up to 10,000 units • ^ MW = ^ viscosity • ^ Branching = decreased viscosity– more compact • decreased radius of gyration – decreased interactions w/other gums – ^ hydrogen bonding w/water |
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Alginates |
• Salts of alginic acid (Ca, Mg, Na) • Linear heteropolymer • Mannuronic acid and guluronic acid |
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Alginates properties |
• Absorbs water and swells • Gels formed by acid precipitation or byaddition of calcium salts – no heat needed! • Cross-linking with polyvalent cations • Gels stable to heat and pH changes |
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Alginates functions in food systems |
– Thickeners and emulsifiers: • Chocolate milk • Ice cream • Sauces • Pie fillings – Gelling agent: • Jellies, jams |
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Carageenans |
• Sulfated polysaccharides • Extracted from red seaweed (Irish moss) • D-galactose and 2,3,6, anhydrogalactose • Several polymers: kappa and lambda important infoods • # and position of sulfate groups effectproperties |
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Kappa Carageenan |
gelling |
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Lambda Carageenan |
nongelling |
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Carageenans properties |
• Interact synergistically w/othergums: – ^ Viscosity, gel strength • Gel formers, thickeners,emulsifying agents, stabilizers |
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Carageenans in foods |
• Chocolate milk: carrageenananion interacts w/protein.Prevents chocolateprecipitation. • Salad dressings, puddings, icecream, … |
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Xanthan Gum |
• Bacterium Xanthomonas campestris • Beta-1,4, linked glucose units • Cellulose backbone • Trisaccharide branches on C3 (mannose,glucuronic, mannose) |
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Xanthan Gum Properties |
• Very high molecular weight • Soluble in hot and cold water • Stable over large pH range |
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Xanthan Gums properties in foods |
• Heat stable • Very viscous • Stabilizer, thickener • Salad dressings, ice cream, juice… • Freeze-thaw stability and syneresis infrozen starch thickened foods • Syrups: CMC or xanthan gum used to buildback viscosity lost due to lower dissolvedsolids level in reduced calorie syrups |
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Guar Gum |
• Guar seeds • 1,4-mannose backbonewith 1,6-galactose branch |
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Guar Gum Properties and roles in food |
• Hydrates in cold water • Very viscous in solution • Viscosity synergism w/wheat starch • Ice cream, dressings, sauces |
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Dietary Fiber |
• Produced by plants • Primarily cell wall structural polysaccharides • Poorly defined– “Group of substances exhibiting various degrees ofresistance to human digestion” • Soluble and insoluble forms • Branched or linear • Homopolymers and heteropolymers |
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Five main types of natural dietary fiber |
– Cellulose, lignin, hemicellulose, pectin, andgums |
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Dietary Recommendations of Fiber |
– Women, ~25 g/daily – Men, ~35 g/daily |
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Fiber rich foods |
Artichoke, lima beans, green peas, raspberries, prunes, oatbran, whole wheat, broccoli, avocado, oats, sweet potato, pecans, peanuts, carrots, apples |
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Cellulose |
• Long linear polymer • Beta 1,4 linked glucose units • Thousands of subunits • Water insoluble |
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Micro-crystalline Cellulose (MCC) |
• Used in foods/beverages: – Bulking agent in low-calorie foods – Source of dietary fiber – Thickener – Anti-caking agent – Stabilizes emulsions |
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Carboxymethylcellulose |
• Aka cellulose gum • Chemically modified cellulose – Sodium hydroxide & chloroacetic acid • Dissolves in cold water, clear insolution |
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Characteristics |
– Thickener – does not gel – Water binder (syneresis control) – Suspending agent – Foam & emulsion stabilizer |
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Applications |
– Sugar free products – Beverages – Baked goods – Reduces fat uptake in fried foods – Sauces, syrups, toppings – Dry blends – Ice cream stabilizer |
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Hemicellulose |
• Heterogenous group of substances • Variety of sugars in backbone and sidechain • Backbone: xylose, mannose, galactose • Side chains: arabinose, galactose, uronicacid • Water insoluble • 50-200 units |
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Lignin |
• Randomnoncarbohydratepolymer • < 50 phenol units • Often covalently linkedto hemicellulose (cellwall) • Water insoluble |
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Pectin |
• Pectic substances • Soluble in hot water • Forms gels • Backbone of linear alpha 1,4, galacturonicacid• ^ Hydrophilicity due to OH and COOH groups • Forms gels with calcium and magnesium |
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Pectin Sources |
Sugar beets, apples, citrus peel |
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Applications |
– gelling agent – ensures consistent setting – improves thermal stability of gels – kosher and vegetarian formulas – yogurt, fruit snacks, jams, jellies,condiments, candies, pharmaceuticals,and supplements. |
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Fructooligosaccharides |
– Sucrose oligomers with 1, 2, or 3fructose units added – Natural: beets, banana, tomato, onion – Manufactured: fungal enzyme action onsucrose – pre-biotic additive – non-caloric; non-cariogenic; 1/3sweetness of sucrose |
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Inulin |
– linear fructosemolecules (2-60 units) – Beta 1,2 linkages – chicory root extract – soluble inhot water |
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Inulin in foods |
• non-digestibleprebioticoligosaccharide • fat replacer and fibersource in cheese,ice cream, spreads,yogurt, chocolate, … |
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Beta Glucan |
– Branched glucosepolymer – Sources: • Yeast cell wall • Oat, wheat and barleyfiber – Mixture of β 1,3-glucanand β 1,6-glucan. – Oats and barley containa mixture of β 1,3-glucanand β 1,4-glucan. |
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Resistant Starch |
– Long chain α 1,4 glucose polymer – Acts like fiber physiologically • resistant to digestion • not absorbed in small intestine – Fermented in large intestine – Natural component of some foods – Retorting, high temperature drying, and bakingcan increase RS levels in food – Processing can also destroy some forms of RS infood |
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RS 1 |
partially milled grains, seeds, andlegumes |
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RS 2 |
in green bananas, rawpotatoes, uncooked starch |
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RS 3 |
incooked-cooled potatoes, bread crusts, breakfastcereals |
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RS 4 |
Modified resistant starch |