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water activity

Chemical reaction by “water activity”Master's course 2st Jun Joon YoungMoisture in foodIntra cellular and extra cellular component in plants and animalstexturetasteShelf lifeExistence of MoistureFree liquid (substance dissolved or dispersed) -as dispersed phase in some emulsified products (eg. Butter, magarin)Hydrates (eg. starch)Imbibed water in gelAbsorption on surface of solidsFree water and bound waterFree water1. Act as solvent (salt, sugar, soluble protein) 2. High melting point, boiling point, specific heat 3. Strong surface tension 4. High viscosityBound water1. Can't act as solvent 2. Low melting point (other liquids such as ethanol melt at a much lower temperature than 0℃) 3. Higher boiling point than 100℃ 4. Larger Density than free water (because, hydrates with salt, sugar, soluble protein) 5. Not available at the growth of microorganism 6. Oven at the higher pressure, the bound water can not be separate from food.Water activityIn 1952, W.J.scott came to the conclusion that the storage quality of food does not depend on the water content, but on water activity(aw)Aw = P/P0 = ERH/100 - ERH = aw × 100P = partial vapor pressure of food moisture at temperature T P0 = saturation vapor pressure of pure water at T ERH = equilibrium relative humidity at TEx) 1mol sugar is contained in the food that includes 1000g water water activity?1000 + 342 18 342= 0.98231000 18Water activity =........4.1101.5802.830.9003.4801.3402.310.9202.7201.0801.770.9401.9200.7701.200.9601.0300.4180.6070.9800.5340.2510.3000.9900.2720.1010.1500.995Sucrose conc.CaCl2 conc.NaCl conc.Water activityWater activity(25℃) and NaCl, CaCl2, sucrose concentration(molel)Water activity Fruit 0.97 Vegetable 0.97 Juice 0.97 Egg 0.97 Meat 0.97 Cheese 0.96 Bread 0.96 Jam and jelly 0.82~0.94 . . Sucrose 0.1Moisture(%,H2O)Chemical reaction and water activityBrowning rate (O.D/gram×100)Storage life(day)55℃75%RH (aw=0.75)31%RH (aw=0.31)0.1%RH (aw=0.001)Browning reaction rate include sucrose model systemMoisture sorption isothermsMoisture content(%)Water activitydesorptionadsorptionSlop and the point of inflection are influenced by water-binding capacity.BET adsorption theoryM1M2ⅠⅡⅢMoisture content(%)RH(%)Moisture sorption hysteresisMdesorptionintermediateadsorptionBet equationP0a1Ca1Ca(P0-P)P×C-1+1=P(1-1)a = moisture content(g/100g) at P P = vapor pressure of food moisture P0 = vapor pressure of pure water C = heat of adsorption constant a1 = adsorption moisture content(g/100g) on monomolecular wallIf.. × 100P0a1Ca1Ca(P0-P)P×100 ×C-1+100=P(100)(1-2)ERHa1C100a1CC-1a(P0-P)P(100)ERH{nameOfApplication=Show}

인문/어학| 2006.11.07| 16페이지| 1,000원| 조회(398)

water activity

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식품의 화학적인 변화

Chemical deterioration in foodMaster's course 2st, Jun Joon YoungStarch(Gelatinzation)2. β-starch α-starchH H2O H 1. R - O O - R R - O O - R R - OH H H H2O R – OHH H R - O O - R H - O - H gelatinzationcoolingheatingheating+H2Oheating+H2OSemi crystalamorphous3. Effect factors ㅡ moisture and temperature : high - increase ㅡ pH : high(alkali) - increase ㅡ salts and ion : existence - increase (OH I- Br- Cl- )Breaking of micellStarch granules contain both linear amylose and branched amylopectin.Raw, uncooked starch granules heated in waterSwellingcoolingwaterwaterwaterwaterwaterwaterwaterheating1. Inverse reaction of gelatinization 2. α-starch β-starch 3. Effect factors ㅡ amylose and amylopectin content ㅡ misture content 30~60% (if, low and high - difficult to bind between molecule and molecule) ㅡ temperature : low - increase (the reaction decrease at -20℃. Because, mobility of molecule is slow.)Starch(Retrogradation)coolingDenaturationof proteins involves the disruption and possible destruction of both the secondary and tertiary structures. disrupts the normal alpha-helix and beta sheets in a protein and uncoils it into a random shape. occurs because the bonding interactions responsible for the secondary structure (hydrogen bonds to amides) tertiary structure are disrupted. in tertiary structure there are three types of bonding interactions between side chains including: hydrogen bonding , salt bridges, disulfide bonds. process is the precipitation or coagulation of the protein.Protein(denaturation)Denaturation(Heat)Heat can be used to disrupt hydrogen bonds and non-polar hydrophobic interactions. This occurs because heat increases the kinetic energy and causes the molecules to vibrate so rapidly and violently that the bonds are disr- upted. Example) The proteins in eggs denature and coagulate during cooking.Denaturation(alcohol)Denaturation(acid or base)Rancidity of lipidTwo types of rancidityUndesirable flavour Nutrition lossEnzymeoxygenRancidity(enzyme)━ pancreatic lipase ━━ gastric lipase ━Rancidity(oxygen)Mechanism of autoxidation1. Initiation reaction R H R + H 2. Chain reaction O2 R ROOH free radical hydroperoxide ROO RH peroxy radical oil molecule 3. Termination reaction ROOH R CO or R CHO R COOH hydroperoxide ketone aldehyde acidEnergy(heat,light)Factors affecting autoxidation1. Energy in the form of heat and light 2. Catalysts (Metal) 3. Double bonds 4. Enzymes 5. Oxygen contentIf, All case is high content - increase But, oxygen is exceptionEffect of metalCu+ROOHROOH-Cu++Cu+H+ROOROOHCu++ROOHROROOH+OH-H2O+++++++++2····Induction of autoxidationInductionFormation of Peroxide compoundPolymerizationOxygen uptakeviscocityPeroxide compoundBrowning reaction(enzymatic)1. Polyphenol oxidase OH O + ½ O2 OH O catechol(dyed color) benzoquinone(dark brown)catecholase2. Tyrosinase NH2 NH2 CH2-CH-COOH HO CH2-CH-COOH HO HO tyrosin dihydroxyphenylalaninetyrosinase+O hydroxylationNH2 O CH2-CH-COOH HO COOH O HO NH Dihydroxyphenylalanine-quinone dihydroxy indole carboxylic acidtyrosinaseO COOH O NH (red color)Browning reaction(non-enzymatic)Primary step H NH-R H OH H NH-R C C C H - C – OH H- C- OH C- OH HO-C – H O+RNH2 HO-C- H O HO-C- H H – C – OH H- C- OH H- C- OH H – C H – C H- C- OH CH2OH CH2OH CH2OH D-glycose D-glycosylamine D-fructosylamine (enol-form)H- C =O H- C= O CH CH C- OH C= O CH HOH2C-C C -CHO C- H H- C- OH CH O H- C- OH H- C- OH hydroxy methyl furfural CH2OH CH2OH 3-deoxyosone 3,4-dideoxyosone (enol-form) melanoidindehydroxyltionAmadori-RNH2-H2O-H2OBrowning reaction(ascorbic acid)O = C O= C COH C =O COH O C =O O HC HC HO C H HO C H CH2OH CH2OH L-ascorbic acid dehydroascorbic acid+O2+H2COOH C HO C= O C C= O HC OH C H HO C H C H O CH2OH 2,3-diketogulonic acid C H furfural+O2+H2+CO2↑Brown compound Formation !+H2OBrowning reaction(caramelization)HO - CH CH - OH CH CH H - C C - H HOH2C-C C -CHO HOH2C OH H O CHO O hexose hydroxy methyl furfural-3H2OdehydrationcaramelheatRole of vitaminVitamin A — is needed for growth and to keep eyes and skin healthy. Vitamin B — is also used for healthy skin and blood. Vitamin C — helps to repair damaged tissue and helps to maintain strong bones and teeth. Vitamin D — controls the mineral content of bone and promotes strong teeth and bones. Vitamin E — protects body cells from deterioration(oxidation). Vitamin K — helps the blood to clot, promoting a smooth and even flow of blood throughout the bodyDegradation of B-caroteneFactor of quality deteriorationfumizationinsectHeating, pH controlEnzymeHeating, Aw controlMicroorganismbiologicalAw control, not used metal vesselMetalBufferpHVaccum, antioxidant, Aw controlOxygenChemicalShade the lightLightRefrigeration, freezingTemperaturedryingMoisturePhysicalprotectionfactorsThank for your attention!{nameOfApplication=Show}

자연과학| 2006.11.07| 23페이지| 1,000원| 조회(348)

식품화학, 저장, 성분, 일반성분

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