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Carbohydrates in Foods

Carbohydrates in Foods. Carbohydrates. Aldehyde or ketone compounds with multiple hydroxyl (-OH) groups C m (H 2 O) n One of the four major classes of biomolecules Make up most of organic matter on earth Have multiple roles in living organisms

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Carbohydrates in Foods

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  1. Carbohydrates in Foods

  2. Carbohydrates • Aldehyde or ketone compounds with multiple hydroxyl (-OH) groups Cm(H2O)n • One of the four major classes of biomolecules • Make up most of organic matter on earth • Have multiple roles in living organisms • Energy source (starch in plants, glycogen in animals) (ATP is phophorylated sugar) • Metabolic intermediates • Part of RNA and DNA (ribose and deoxyribose sugars) • Cell wall of bacteria and plants (cellulose in plants) • Linked to many proteins and lipids (e.g., glycoproteins)

  3. Monosaccharides • The simplest carbohydrates • Aldehydes or ketones with 2 or more–OH groups • (CH2O)n • n = 3 (trioses 3 C) is the smallest - glyceraldehyde  aldosecontaining an aldehyde group - dihydroxyacetone  ketose containing a keto group

  4. ketose aldose • Glyceraldehyde has a single asymetric carbon  2 stereoisomers (D- and L- configuration) • tetroses  4 C pentoses  5 C hexoses  6 C (e.g., glucose and fructose) heptoses  7 C • Consider D- and L- at the farthest C from from the aldehyde or ketone group. • aldose  C1 at CHO ketose  C1 at CH2OH • If n = asymmetric C or chiral carbon atom, the number of stereoisomers = 2n

  5. Aldose - one terminal carbonyl (C=O) group Ketose - one non-terminal carbonyl group • Enantiomers = stereoisomers which are mirror image of each other (i.e., D-form and L-form) • Diastereoisomers = stereoisomers which are not mirror image of each other (e.g., D-erythrose and D-threose) • Epimers = stereoisomers which are different only at a single asymetric atom (e.g., D-glucose and D-mannose at C2) • Anomers = stereoisomers which are different only at an anomeric carbon atom (e.g., -D- and -D-glucose at C1 ; -D- and -D-fructose C2)

  6. The predominant forms of glucose and fructose are not open chains. • The open-chain forms can cyclize into rings. - glucose reaction of the OH group at C5 with CHO group at C1 forming a six-member ring called pyranose - fructose reaction of the OH group at C5 with CO group at C2 forming a five-member ring called furanose - fructose can also be present as pyranose (predominant in free state) - Additional asymetric C is created  OH group can be up () or down ()

  7. In water, -D-glucose and -D-glucose interconvert (called mutarotation) through the open-chain form to give an equibrium mixture ( 33%,  66%, and open-form 1%). • The pyranose ring is not flat but can be in chair (predominant) and boatconformations • The furanose ring is not flat but can be in envelopeconformations

  8. Disaccharides • Formed by formation of a glycosidic linkage/bond between two monosaccharide molecules • ROH + R'OH  R-O-R' + H2O involving -OH bonded to anomeric carbon of a cyclic sugar • C12(H2O)11 • Glycosidic bonds (C-O-C) between monosaccharide units are the basis of oligosaccharide and polysaccharide formation • - or - anomers can be bonded to any –OH on the other sugar

  9. The carbons which participate in a glycosidic bond are numbered. • For example, two molecules of -D-glucose can be bonded by (14) or (16) • Non-reducing end and reducing end can occur. • Common disaccharides are sucrose, maltose, and lactose. • Matose, lactose  reducing sugars Sucrose  non-reducing sugar • Maltose has (14) glucose and glucose lactose has (14) galactose and glucose sucrose has ,(12) glucose and fructose

  10. Sucrose can be hydrolyzed by a) warm diluted acid b) sucrase or invertase to glucose and fructose (invert sugar = the mixture of glucose and fructose). • The hydrolysis of sucrose = inversion • Sucrose (+) rotation (dextrorotatory) glucose (weakly +) fructose (strongly -) invert sugar (-) rotation (levorotatory) • Jam processing, yeast fermentation  inversion

  11. Oligosaccharides • Sucrose – from cane, beet Lactose – from milk, hydrolyzed by lactase in humans and -galactosidase in bacteria Matose – from starch hydrolysis, hydrolyzed by maltase • Containing 2-20 monosaccharide units linked by glycosidic bonds • Disaccharides, trisaccharides (maltotriose) (raffinose = Gal-Glu-Fru), tetrasaccharides (stachyose = Gal-Gal-Glu-Fru)

  12. Polysaccharides • Condensation polymers of monosaccharides • High MW – macromolecules, colloids • General fomular (C6H10O5)n • Glucose is the commonest monosac. unit. • 2 classes - homopolysaccharides – one type of monosaccharides - heteropolysaccharides – more than one type of monosaccharides

  13. Structure of polysaccharides vary in - type of monosac. units - order or sequence of monosac. units - type of glycosidic linkages (e.g., - for structural cellulose, and chitin; - for storage starch and glycogen) 1. Starch – only in plants, low osmotic potential - occurs in 2 forms - -amylose and amylopectin – different in degree of branching - MW 5000-500,000 - only -D-glucose - amylose – linear, linked by -1,4 glycosidic bonds, forms helical coils hydrated with water (6 glucose units per turn), blue complex with iodine

  14. - amylopectin – highly branched, length of each branch ~ 25-30 glucose units, linked by -1,4 in linear and -1,6 glycosidic bonds at branching points, reddish violet complex with iodine 2. Glycogen – only in animals (liver, muscle), low osmotic potential - similar to amylopectin - branched-chain polymer of -D-glucose - linked by -1,4 in linear and -1,6 glycosidic bonds - but degree of branching (length of each branch ~ 10 glucose units) and MW are higher than amylopectin

  15. 3. Dextran - storage polysaccharide in yeast and bacteria - only glucose residues - but nearly all linkages are -1,6 branching linkages are -1,2 or -1,3 or -1,4 4. Cellulose - structural componet in plant cell wall - only glucose residues – no branching - linked by -1,4 forming straight chain (each unit is 180 to each other, H-bonds form)  high tensile strength for fibers

  16. - mamals have no cellulase, ruminants have bacterial cellulase in digestive tracts - fungi also produce cellulase 5. Chitin - in exoskeletons of insects and crustacea - similar to cellulose - only N-acetyl- - D-glucosamine residues (glucose substituted with N-acetylamino group for OH group at C2) amino sugar - linked by -1,4 - H-bonds form in each chain  mechanical strength

  17. 6. Pectin - in plant cell wall - mostly D-galacturonic acid residues (galactose in which OH at C6 has been oxidized to a carboxyl group)  sugar acid Lignin - nonpolysaccharides - a polymer of coniferyl alcohol - very tough and durable material in wood - part of dietary fiber and crude fiber

  18. 7. Other Polysaccharide Hydrocolloids • hydrocolloids  viscosity, gel • polysaccharide hydrocolloids – most are heteropolysac. 7.1 Plant exudates - gum arabic or gum acacia - gum tragacanth - gum karaya 7.2 Seed gums - Locust bean gum - Guar gum 7.3 Seaweed extracts - Carrageenan - Algin or Alginate - Agar

  19. Gum arabic

  20. Gum karaya

  21. Locust bean gum

  22. Guar gum

  23. Guar gum

  24. Carrageenan

  25. Agar agar

  26. Alginate

  27. 7.4 Microbial gums - Xanthan gum - Gellan gum - Nata de coco 7.5 Cellulose derivatives - Carboxymethylcellulose (CMC) - Methylcellulose - Hydroxypropylcellulose Inulin - fructo-oligosaccharide or oligofructose fructans - mostly (2-1) fructosyl-fructose linkage, chicory - glucose can be found at the end of the fructose chain  G(F)n , a chain length 2-20 fructose units - health benefits (soluble fiber, prebiotic)

  28. Nata de coco

  29. Starch • Polymer of glucose – amylose and amylopectin • Stored in form of starch granules in plant cells • Granule size, shape, and ratio of amylose and amylopectin depends on type of plant • Degree of polymerization (DP) of amylose and amylopectin depends on type of plant (high DP  high MW) • Starch properties depend on type of plant

  30. Properties of starch 1. Gelatinization (not gelation) - occurs when starch granules are heated in water - heat vibrates H-bonds between starch molecules  water molecules can form H-bonds with starch - then, starch granules swell – less free water, friction – viscosity increases - clarity increases - loss of birefringence - after reaching the highest swelling  granules break down  viscosity decreases

  31. 2. Retrogradation - after gelatinization starch molecules are dispersed in water forming H-bonds - upon cooling  starch molecules rearrange to form H-bonds with themselves instead of water  3D-structure - at low concentration + slow cooling  sedimentation - at high concentration + fast cooling  gel network, increased viscosity - water molecules are squeezed out  can cause syneresis - amylose tend to show stronger retrogradation than amylopectin

  32. - retrogradation  bread staling, product texture • Modified starches - to improve native starch properties by 1. Physical methods – heat, milling 2. Chemical methods – chemicals, enzymes 3. Biotechnology – genetic engineering 4. Combination - some examples of starch modification 1. Pregelatinization 2. Substitution – esterification (starch acetate, monophosphate), etherification (hydroxypropyl starch)

  33. 3. Cross-linking – links between starch chains (distarch phosphate) 4. Acid-thinning 5. Oxidizing • Starch hydrolysis 1. Dextrinization or pyroconversion – heat starch and acid in dry conditions  dextrin 2. Liquefaction – hydrolysis of gelatinized starch by acid and/or enzymes  maltodextrin (DE <20) 3. Saccharification – high degree of hydrolysis glucose syrup • DE = Dextrose Equivalent = content of reducing groups as % glucose by weight = 100/DP

  34. Pectin • Present in plant cell wall with cellulose • Polymers of D-galacturonic acid (-1,4) • COOH can be esterified by CH3 methoxyl ester COOCH3 • Protopectin – high methoxyl (high DM, high DE) pectinic acid – some methoxyl pectic acid – no methoxyl • High-methoxyl pectin (> 50%)  acid, high sugar - rapid-set pectin (>70%) - slow-set pectin (50-70%) – forms gel at lower T • Low-methoxyl (<50%) Ca2+, low sugar

  35. Sugar alcohols - sugar derivatives - polyhydric alcohols, polyols - CHO is substituted by CH2OH by hydrogenation or fermetation of sugars - e.g., sorbitol, mannitol, xylitol - lower calories, slowly absorbed, reduced tooth decay, cooling effect - chewing gums, confectionery • Sugar sweetness - depends on type of sugar

  36. LAB • Starch extraction – cell disruption  centrifuge • Microscopy of starches - 1% of starch suspension (1 water : 1 glycerol) - iodine solution Record - characteristics of starch granules (e.g., size, shape, iodine complex)

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