第一章植物学基础2-营养与食品卫生

第一章营养学基础碳水化合物CarbohydratesMaincontentsDefinitionofcarbohydratesClassificationofcarbohydratesDigestion&absorptionofCHOFunctionsofcarbohydratesDisordersrelatedtoCHOmetabolismDietaryreferenceintakesofCHOsCarbohydratesareoneofthethreemacronutrienttypesthatprovideenergytoourbodies.Carbohydratescontaincarbon,hydrogen,andoxygen.

碳水化合物：属三大能量营养素之一，主要由碳、氢、氧构成。一、碳水化合物的定义

Whatarecarbohydrates?Carbohydratecanbeabbreviatedas“CHO”.Weobtainedcarbohydratespredominantlyfromplantfoodssuchasfruits,vegetables,andgrain.Why?PlantsmakecarbohydratesthroughtheprocessofphotosynthesisEnergyfromsunCarbondioxidefromairGlucosestoredinplantWaterWater+CarbondioxideGlucose光合作用二、碳水化合物的分类

ClassificationofcarbohydratesCarbohydratesSimpleComplexDisaccharidesMonosaccharidePolysaccharidesOligosaccharide寡糖单糖双糖多糖HOHCH2OHHOHOHHOHHHGlucoseOHOHHOHHOHCH2OHCH2OHFructoseHOOHOHOHHHHHCH2OHGalactoseThethreemostcommonmonosaccharides.ALLofthemcontainidenticalatoms……StructureofmonosaccharidesMonosaccharides-Glucose（葡萄糖）Glucoseisthemostabundantsugarmoleculefoundinourdietsandinourfoods.Glucosedoesnotgenerallyoccurbyitselfinfoodsbutattachestoothersugarstoformdisaccharidesandcomplexcarbohydrates.Inourbodies,glucoseisthepreferred

sourceofenergyforthebrain.食物中最多的单糖，但不以单独形式存在，常与其他糖形成双糖或多糖的形式存在，葡萄糖优先为大脑提供能量。Monosaccharides-Fructose（果糖）Fructoseisalsocalledfruitsugar.Fructoseisthesweetestnaturalsugar,occursnaturallyinfruitsandvegetables.PrefixMonosaccharides-Galactose（半乳糖）Galactosedoesnotoccuraloneinfoods.Itjoinswithglucosetocreatelactose,oneofthedisaccharides.Sweetestmonosaccharides?Themostabundantmonosaccharides?Thesweetest：fructoseThemostabundant：glucoseDisaccharide（双糖）Disaccharide:Acarbohydratecompoundconsistingoftwosugarmoleculesjoinedtogether.Thethreemostcommondisaccharidesfoundinfoods

arelactose（乳糖）,maltose（麦芽糖）,andsucrose（蔗糖）.Disaccharides–Lactose（乳糖）＋GlucoseGalactoseLactose

Lactose:Consistofoneglucosemoleculeandonegalactose

(半乳糖）

molecule.Disaccharides—Maltose（麦芽糖）Maltose:alsocalledmaltsugar,consistoftwomoleculesofglucose.Itdoesnotgenerallyoccurbyitselfinfoods,butresultsasaby-productofdigestion.＋GlucoseDisaccharides—Sucrose（蔗糖）Sucroseiscomposedofoneglucosemoleculeandonefructose（果糖）

molecule.

＋Sucroseprovidesmuchofthesweettastefoundinhoney,fruits,andvegetables.HowabouttheSucroseandfructose?Sweeterthanlactoseormaltose,why?哪种双糖最甜--麦芽糖，蔗糖，乳糖？麦芽糖--2个葡萄糖蔗糖--1个葡萄糖+1个果糖乳糖--1个葡萄糖+1个半乳糖蔗糖Oligosaccharide（寡糖）Oligosaccharidearecomposedof3to10monosaccharides.Themostcommonoligosaccharidesare

raffinose

（棉籽糖）andstachyose（水苏糖）.

Theycannotbedegradedbyenzymesinthesmallintestine,butcanbebrokedowninthelargeintestine.Polysaccharides（多糖）Polysaccharidesincludestarch（淀粉）,glycogen（糖原）andmostfibers（纤维）.PolysaccharidesStarchGlycogenFiber淀粉糖原纤维Polysaccharide--StarchStarch:Apolysaccharidestoredinplantsandisthestorageformofglucoseinplants.（淀粉是葡萄糖在植物中的贮存形式）

Excellentfoodsourcesofstarchinclude?grains(wheat,rice,corn,oats,andbarley),legumes(peas,beans,andlentils),andtubers(potatoesandyams).

Ourbodieseasilydigestmoststarches，wecallthemdigestiblestarch(可吸收淀粉）.根据其结构可分为直链淀粉（amylose）和支链淀粉（amylopectin），前者易使食物老化，后者易使食物糊化（gelatinization）。However,somestarchinplantsisnotdigestibleandiscalledresistantstarch（抗性淀粉）.抗性淀粉：指健康者小肠中不吸收的淀粉及其降解产物。

Whenourintestinalbacteriatrytodigestresistantstarch,afattyacidcalledbutyrateisproduced.Consumingresistantstarchmaybebeneficialbecausebutyrateissuggestedtoreducetheriskofcancer.

豆科食物（Legumes）含有的抗性淀粉比谷类、蔬菜和水果多。BeansproutGreensoybeanGlycogen:Apolysaccharidestoredinanimals,includinghumans.Verylittleglycogenexistsinfood.Thus,glycogenisnotadietarysourceofcarbohydrate.Polysaccharide-Glycogen（糖原）Whichtissuesareabundantinglycogen?Westoreglycogeninourmusclesandliver.Wecanbreakdownglycogenveryquicklyintoglucosewhenweneeditforenergy.Basedonthewatersolubleability,fibercanbeclassifiedintosolublefibersandinsolublefibers.Insolublefibers（不溶性纤维）:cellulose（纤维素）,hemicellulose（半纤维素）

andxylogen（木质素）.Solublefibers（可溶性纤维）:果胶（pectin)，树胶和粘胶.

Polysaccharide--Fiber膳食纤维（dietaryfiber）：是指植物性食物或原料中糖苷键大于3个，不能被人体小肠消化和吸收，但对人体健康有意义的碳水化合物。膳食纤维包括部分非淀粉多糖（纤维素、半纤维素、木质素、果胶等）、抗性淀粉、葡聚糖以及部分低聚糖等。

(1)增强肠道功能、有利粪便排出

Helpspreventconstipationandotherintestinalproblemsbykeepingourstoolsmoistandsoft.FunctionsofdietaryfiberDietaryfiberincreasesfaecalbulkthroughwaterbindingbyfiber.Fibergivesgutmuscles“somethingtopush”andmakesiteasiertoeliminatestools.

(2)

控制体重和减肥Mayenhanceweightloss,aseatingahighfiberdietcausesapersontofeelmorefull.Fiber

absorbswater,expands

inour

intestine,and

slows

themovementoffoodthroughtheupperpartofthedigestivetract.

(3)降低血糖和血胆固醇Decreasethelevelofbloodsugarandcholesterol

Mayreducetheriskofheartdiseasebydelayingorblockingtheabsorptionofdietarycholesterolintothebloodstream.(4)降低结肠癌的发病风险Mayreducetheriskofcoloncancer.Whilethereisstillsome

controversysurroundingthisissue,manyresearchersbelievethatfiberbindscancer-causingsubstancesandspeedstheireliminationfromthecolon.

三、碳水化合物的消化及吸收WehavelearnedmanyformsofCHOscontaininginourfoods,whichoneistheformofenergyusedbyourbodies?TheprimarygoalofCHOdigestionistobreakdownpolysaccharidesanddisaccharidesintomonosaccharidesthatcanbeconvertedtoglucose.Digestionofcarbohydratesinfoods(Inthemouth)CHOdigestionbeginsinthemouth.Question:Whenyoueatsteamedbread（馒头）,noticethatyoucanactuallytasteitbecomingsweeter,Why?Salivaamylase（淀粉酶）

breaks

starch(淀粉）

intosmallerparticlesandeventuallyintothemaltose（麦芽糖）.Disaccharidesarenotdigestedinthemouth.Inthestomach,alldigestionofCHOsceases.Digestionofcarbohydratesinfoods(Inthestomach)Becausetheacidinthestomachinactivatesmostofthesalivaryamylaseenzyme.Wouldyouguessthereasons?Themajorityofcarbohydratedigestionoccursinthesmallintestine.Digestionofcarbohydratesinfoods

(Inthesmallintestine)Pancreaticamylasesecretedbythepancreasintothesmallintestine.Pancreaticamylasecontinuestodigestanyremainingstarchintomaltose（麦芽糖）.Additionalenzymesfoundintheintestinaltractbreakdowndisaccharidesintomonosaccharides.MaltoseSucroseLactoseGlucoseGlucose&FructoseGlucose&GalactoseMaltaseSucraseLactaseAbsorbedbymucosalcellsBloodstream麦芽糖蔗糖乳