《食品化学》课程教学课件（国外讲稿）03 Carbohydrates part1

3/2/14 Carbohydrates Part One The most abundant organic molecules Initial source of ALL FOOD ·Provide ·Energy(~4CaVg) ·Carbon ·Fiber Significant contribution to the properties of foods Where is Sugar in Food? Contributions to Food Properties -Sweetness .Precursors of aroma compounds .Precursors of colored compounds Added sugar .Provide texture r found in .Cellulose Candy.ch .Starch Soft drinks .Pectin ts.snacks Build viscosity at low concentration .Starch com syrup .Gums .Cellulose fragments

3/2/14& 1& Carbohydrates Part One Carbohydrates • The most abundant organic molecules • Initial source of ALL FOOD • Provide • Energy (~4 Cal/g) • Carbon • Fiber • Significant contribution to the properties of foods . Where is Sugar in Food? Naturally found in: Fruits, vegetables, grains, dairy products Added sugar found in: Candy, chocolate Desserts, baked goods, ice cream Soft drinks Condiments, snacks On labels as sugar, sucrose, invert sugar, corn syrup Contributions to Food Properties •Sweetness •Precursors of aroma compounds •Precursors of colored compounds •Provide texture •Cellulose •Starch •Pectin •Build viscosity at low concentration •Starch •Gums •Cellulose fragments

3/2/14 ClassifieationsacuMupa2 Polysaccharides .Monosaccharides -Polysaccharides .Polyhydroxy aldehydes .Starch .Polyhydroxy ketones .Glucose polymer,a-1,4-linkages,1,6 branches Oligosaccharides -Cellulose .Disaccharides .Glucose polymer,B-1,4-linkages .Pectin .Sucrose,Maltose,Lactose "Polygalacturonic acid(methyl esters) .Trisaccharides .Gums ·Raffinose .Carrageenans .Tetrasaccharides -Alginates .Stachyose -Locust bean gum etc. Nutritional Availability Trioses the simplest sugars Readas bed and metabolized H、 =0 H C H-C-OH HO-C-H HC (HCOH) CH2OH CHOH Glycoaldehyde CH2OH Enantiomers- C-0 CH2OH 1,3-0 2

3/2/14& 2& Classifications •Monosaccharides •Polyhydroxy aldehydes •Polyhydroxy ketones •Oligosaccharides •Disaccharides •Sucrose, Maltose, Lactose •Trisaccharides •Raffinose •Tetrasaccharides •Stachyose http://www.chem.qmw.ac.uk/iupac/2carb/ Polysaccharides •Polysaccharides •Starch •Glucose polymer, α-1,4-linkages, 1,6 branches •Cellulose •Glucose polymer, β-1,4-linkages •Pectin •Polygalacturonic acid (methyl esters) •Gums •Carrageenans •Alginates •Locust bean gum •etc. Nutritional Availability •Readily absorbed and metabolized •Glucose •Fructose •(Galactose) •Not Absorbed •Polysaccharides (fiber) •Disaccharides (some diffusion) •Some are hydrolyzed in the intestinal mucosa •Prebiotic oligosaccharides (food for Probiotic bacteria) •Fermentable oligosaccharides can lead to flatulence (gas-producing anaerobes) Trioses the simplest sugars C H C H2OH O Glycoaldehyde (HCOH) C H C O C H2OH H OH C H C O C H2OH HO H Glyceraldehyde(s) Two possible isomers C H2OH C C H2OH O 1,3-Dihydroxyacetone (optically inactive) Enantiomers – non super-imposable mirror images Epimers – sugars that differ by configuration at one carbon

3/2/14 Aldoses D-and L-Isomers Tetroses Aldoses HCOH CHOH H c D-(+)-glyceraldenyde H H-C-OH -OH H-C-OH H CH2OH CH2OH D-()Treose D-(-)-Erythrose CHOH L-glyceraldehyde Tetroses Pentoses Ketoses-the "uloses" Aldoses H C CH2OH CH2OH H-C -OH H-C OH C-0 C-0 H CO H-C H-COH HO-C-H OH HO H -OH HO. H-C OH OH HO- -H CH2OH CH2OH CH2OH H-C OH CH2OH HO-d H OH ge8oge L-glycero-etrulose D-cibose D-xylose CHOH D-arabinose D-lyxose 3

3/2/14& 3& Aldoses D- and L- Isomers D-(+)-glyceraldehyde L-(-)-glyceraldehyde C H C O C H2OH H OH C H C O C H2OH HO H the&
conforma1onal&& carbon,&highest8numbered&asymmetric&C& Tetroses Aldoses D-(-)-Threose D-(-)-Erythrose C H C O C HO H C H2OH H OH C H C O C C H2OH H OH H OH C2&Epimer &Not&an&Enan1omer&(complete&mirror&image)& Tetroses Ketoses - the
uloses D-glycero-tetrulose
D-erythrulose C H2OH C C C H2OH O H OH C H2OH C C C H2OH O HO H L-glycero-tetrulose Pentoses Aldoses D-ribose D-arabinose D-xylose D-lyxose C C C C C H2OH OH OH OH H H H H O C C C C C H2OH OH OH H H H O HO H C C C C C H2OH OH H OH H HO H H O C C C C C H2OH H H OH HO HO H H O

3/2/14 Pentoses Ketoses CH2OH CHO c=o -0 CHO H-C-OH HO-d H-C-OH CHOH H-C-OH CHOH CH.OH CHOH CH.OH CHOH CHOH etoam Hexoses but only 4 D-ketohexoses,or hexuloses Table2 Moncacchari prices CH OH CH.OH CH2OH 0 0 CH2OH 4

3/2/14& 4& Pentoses Ketoses D-ribulose (erythro-pentulose) D-xylulose (threo-pentulose) C H2OH C C C C H2OH OH OH H H O C H2OH C C C C H2OH H OH O HO H Hexoses Aldoses - there are 8 D-aldohexoses D-(+)-allose CHO C H2OH CHO C H2OH CHO C H2OH CHO C H2OH CHO C H2OH CHO C H2OH CHO C H2OH CHO C H2OH D-(+)-mannose D-(-)-gulose D-(-)-idose D-(+)-galactose D-(+)-talose D-(+)-altrose D-(+)-glucose Hexoses but only 4 D-ketohexoses, or hexuloses C H2OH O C H2OH C H2OH O C H2OH C H2OH O C H2OH C H2OH O C H2OH D-(+)-psicose D-(-)-fructose D-sorbose Natural isomer appears to be L￾D-(-)-tagatose

3/2/14 Two Carbonyls? No Carbonyls? Oddly-placed Carbonyls? Sugar alcohols Dialdoses odialdose"instead of"ose" e.g.,glucodialdose CH2OH CH-OH Ketoses at C2 -ulose"e.g.xylulose Ketoses elsewhere CH2OH CH2OH e.g.,at C3.called a 3-ketose or hexo-3-ulose CH.OH Diketose CHOH CHOH Diuloses- Mixed ketose and aldose Sorbatol aldoketoses,aldosuloses Sugar Alcohols Xylitol 5 carbon sugar alcohol. Many sugar alcohols exist naturally in nature approximate sweetness of especially plants sucrose. anti-&non-cariogenic .e.g.sorbitol,mannitol,xylitol,etc properties not metabolized by insulin Can also be made artificially presently fairly expensive

3/2/14& 5& Two Carbonyls? Oddly-placed Carbonyls? Dialdoses
-odialdose instead of
-ose e.g., glucodialdose Ketoses at C2
-ulose e.g., xylulose Ketoses elsewhere e.g., at C3, called a 3-ketose or hexo-3-ulose Diketose Diuloses - Mixed ketose and aldose aldoketoses, aldosuloses No Carbonyls? Sugar alcohols Erythritol Threitol Sorbitol Mannitol Xylitol C H2OH C H2OH C H2OH C H2OH C H2OH C H2OH C H2OH C H2OH C H2OH C H2OH (symmetrical)& Sugar&Alcohols& • Many&sugar&alcohols&exist&naturally&in&nature& —&especially&plants& • e.g.&&sorbitol,&mannitol,&xylitol,&etc& • Can&also&be&made&ar1ficially&& Xylitol • 5&carbon&sugar&alcohol.& • approximate&sweetness&of& sucrose.& • an18&&&non8cariogenic& proper1es& • not&metabolized&by&insulin& • presently&fairly&expensive.&

3/2/14 Xylitol-Examples ons acetalsketals Famous reactions Chain lengthening-Cyanohydrin(Kilani-Fischer)Synthesis Sugar Acids N H-OH HO_ H cyanide adduct H-OH H OH CHOH H H20 Na/Hig CHO CHOH hydrolvze the nitrile OH H-C-OH CHOH threose 6

3/2/14& 6& Xylitol&8&Examples& Famous reactions Condensations cyanohydrins acetals, ketals imines hydrazones (Shiff base) R C R' O C N R HO C C N R' R C R' O R C R' O O R" H R HO C O R' R" N H H R" C R' N R R" R HO C N R' R" H Famous reactions Chain lengthening - Cyanohydrin (Kiliani-Fischer) Synthesis C OH C H2OH O H H C N OH C H2OH H H OH C N H OH C H2OH H HO H C N & H2O CHOH OH C H2OH H C O O Na/Hg CHOH OH C H2OH H C O H cyanide adduct hydrolyze the nitrile reduction with sodium amalgam erythrose or threose Sugar Acids 1-acids
onic acids, e.g., gluconic acid pyranoses tend to form lactones, e.g., δ-gluconolactone hydrolyze slowly - gradual acidification 6-acids
uronic acids, e.g., glucuronic acid 1,6-diacids
aric acids, e.g., glucaric acid COOH C C C C C H2OH OH HO OH OH H H H H CHO C C C C COOH OH HO OH OH H H H H C C C C C C H2OH OH HO OH H H H H O O COOH C C C C COOH OH HO OH OH H H H H

3/2/14 Cyclization Cyclization hemiacetals,hemiketals mutarotation hemiacetal hemiaceta (or hemiketal)isstable ne rate determined bypH,et -弹 aandBanomers Cyclic lores Cyclization a-F furanoses and pyranoses pyran OH H B-D-fructopyranose 12421122 furan 153113 B-D-fructofuranose aanomers also exist in solution >

3/2/14& 7& Cyclization hemiacetals, hemiketals C H O C H2OH C C H2OH HO H OH C C H2OH HO H OCH3 H2O C H3OH hydrate hemiacetal α$ β$ Intramolecular hemiacetal (or hemiketal) is stable OH C H2OH O H O C H2OH OH OH OH H H H H OH H O C H2OH OH OH OH H H H H OH H or α and β anomers Cyclization mutarotation The carbonyl carbon that was attacked is called the anomeric carbon the reducing carbon The potentially reducing group α and β anomers are in equilibrium (mutarotation) determined by relative stability Interconversion rate determined by T, pH, etc. α and β anomers are different mp, solubility, crystal habit, etc. Excellent example: lactose O H OH H H H H OH OH OH C H2OH C H2OH C O C C C C H2OH HO H OH OH H H O C H2OH HO C H2 OH OH H H H OH O O Cyclization furanoses and pyranoses β-D-fructopyranose furan β-D-fructofuranose pyran α anomers also exist in solution

3/2/14 Conformational Isomers Chair forms tend to be mare ableboatwould haveecipsed 20 60 Fig.4.5.Temperature dependence of the mutaro- tation equilibrium of D-fructose,(B-D-fructo- )ne nd 行 1975) Stability of Conformers Stability of Conformers steric interaction energies nomenclature,interaction energies ℃， .53 Anomeric .OC2 20 10.03 7.3 8

3/2/14& 8& Conformational Isomers boat twist boat chair Chair forms tend to be more stable - boat would have eclipsed substituents, chair had gauche interactions. But two chair forms are possible; which is preferred? H HO HO H H H C H2OH OH H OH O O C H2OH H OH H OH OH H H OH H Stability of Conformers steric interaction energies Decreasing order of unfavorability Interaction kJ/mole Oax - Cax 10.45 Oax - Oax 6.27 Hax - Cax 3.76 Hax - Oax , Oeq - Ceq, Oax - Ceq 1.88 Oeq - Oeq, Oax - Oeq 1.46 Anomeric O - OC2eq 2.30 Anomeric O - OC2ax 4.18 Stability of Conformers nomenclature, interaction energies H HO HO H H H C H2OH OH H OH O H HO HO H H H C H2OH H OH OH O O C H2OH H OH H OH OH H H OH H O C H2OH H OH H H OH OH H OH H 1C4 4C1 β$ α$ 8.53 33.44 10.03 27.38

3/2/14 Summary of Isomers Enantiomers,Epimers,Anomers Food Sweeteners Sweetness is 1of 5taste modalities. Many compounds may have a"sweet"taste E.g.hydroxy compounds-glycols,sugars mme) there are ote ers however -lead sah图 Per Capita Sugar Consumption BASIC TASTES DER CAPITA CONSUMPTION 20011 emal EQUaL Salty- Bitter Sweet Sour Umam?? 9

3/2/14& 9& Summary of Isomers Enantiomers, Epimers, Anomers - • Structural Isomers • aldoses – ketoses (glucose – fructose) • Configurational Isomers • enantiomers (mirror image) • epimers • D & L- isomers • anomers
epimers at the reducing carbon • Conformational Isomers (conformers) • Boat • Chair, 4C1. Food&Sweeteners • Sweetness&is&1&of&5&taste&modali1es.& • Many&compounds&may&have&a&
sweet&taste.& • E.g.&&hydroxy&compounds&8&glycols,&sugars& there&are&others&however!& – beryllium&salts& – lead&salts& – some&other&amino&acids& – synthe1cs&8&Cyclamate,&saccharin,&aspartame,&etc.& Umami&??& Per&Capita&Sugar&Consump1on&

3/2/14 THE RELATIVE SWEETNESS OF SUOARS Sweetness Sugar -p-Pructose Bource:Shallenberger and Aeree (1971) 60 D-Glucose D-Galactose 20406080 Temperature(C) Fig.4.5.Ten tatior and Birch 1975) 10

3/2/14& 10& D8Fructose& D8Glucose& D8Galactose