1 / 45

Food Carbohydrates

Food Carbohydrates. OLIGOSACCHARIDES. Definition. Oligo- : few in Greek; oligosaccharides contains 1-10 (20) monosaccharide uints. Polysaccharides: >10 or 20. Oligomers, polymers: -mer designates a structure composed of parts. Poly- : many in Greek.

jovanna-aglish
Download Presentation

Food Carbohydrates

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Food Carbohydrates OLIGOSACCHARIDES

  2. Definition • Oligo- : few in Greek; oligosaccharides contains 1-10 (20) monosaccharide uints. Polysaccharides: >10 or 20. • Oligomers, polymers: -mer designates a structure composed of parts. • Poly- : many in Greek • In disaccharides, the aglycon is a monosaccharide unit • Higher order oligosaccharides are named tri-, tetra-, • penta-, hexa-, hepta-, etc. • Structures may be predominately linear or branched.

  3. Structural features Linear: a head to tail linkage 1 reducing end 1 non-reducing end Glycosyl unit Branched: 1 reducing end several to many non-reducing ends reducing end non-reducing end Glycosidic linkage of anomeric carbon and –OH of another unit

  4. Glycosidic linkages • Carbohydrates are polyalcohols  -OH can react with a hemiacetal -OH to split out water and form a glycosidic bond between two residues. • Take D-glucopyranose as an example: -D-glucopyranose could react with –OH at C-2, C-3, C-4 and C-6 of the 2nd unit  4 reducing disaccharides -D-glucopyranose  4 ” ” - and - hemiacetal hydroxyl groups of two residues could react with each other  3 nonreducing disaccharides Total = 11 possible disaccharides

  5. Acid-catalyzed reversion • Glycosic bonds can be hydrolyzed with acid and heat. The reaction is reversible, sugars re-combine in the presence of acid and water-limiting conditions to form mixture of oligomers. • This acid-catalyzed combination of monosaccharides is called reversion. Glycosidic linkage can occur at any OH position (at O-2,O-3 etc) and in  or  configuration. Example: conversion of maltose to cellobiose

  6. Acid-catalyzed reversion -1,4 linkage Maltose 2 glucans Cellobiose: -1,4 linkage

  7. Acid-catalyzed reversion This random reaction has been used for commercial production of the bulking agent Polydextrose:

  8. Polydextrose • Polydextrose is produced by the reversion reaction between D-glucose, sorbitol and citric acid under heat treatment. • Degree of polymerization (DP) is fairly low. • Sold commercially as Litesse and other names.

  9. Maltose • Full name: 4-O-(-D-glucopyranosyl)-D-glucopyranose Exists as - and -anomers. • Reducing sugar. Its glycosidic linkage is acid labile.

  10. Maltose • Obtained from starch by: • - acid hydrolysis (randomness, low yield) • - -amylase (from Bacillus bacteria) • Yield = 80%, higher yield by the action of • debranching enzymes and then -amylase.

  11. Maltose • Maltose is crystallized easily from aqueous solution as -maltose monohydrate, even though in solution the ratio of  to  forms is 1:2. • Maltose uses: mild sweetener for foods and pharmaceuticals, and as a parenteral injectable for slow release of D-glucose.

  12. Lactose • Name: 4-O-(-D-galactopyranosy)- • D-glucopyranose • Reducing sugar • Hydrolyzable with acid • Multiple anomeric forms in solutions • Lactose (milk sugar): 2.0-8.5% • cow/goat milk: 4.5% • human milk: 7.0%

  13. Lactose production (as -lactose monihydrate)

  14. Lactose production • 1pound of cheese  9 lbs whey (4.7% lactose)   0.4 lb lactose • Potential lactose production from whey = 23 billion pounds per year! • Unfortunetely, little commercial use at this time.

  15. Lactose uses • Food : toppings, icings, pie fillings, confections, ice cream • In food, lactose contributes body but little sweetness (~20% of sucrose), enhances colors and flavors. • Pharmaceutical uses: provides bulk and rapid dissolution

  16. Lactose/Lactate • Lactose is relatively high in milk and milk products but lower in fermented dairy products as yogurt, cheeses. • During fermentation, some lactose is converted to L-lactate:

  17. Lactose intolerance (L.I.) • Lactose is digested in small intestine by the hydrolytic enzymes lactase (-galactosidase) located in the brush border epithelial cells. • If lactose is not completely hydrolyzed and absorbed, it will proceed into the large intestine wher anaerobic bacteria ferment the lactose to lactic acids, other short chain acids, CO2, H2 and methane. • This causes the symptom of lactose intolerance: abdominal distention, flatulence, cramping, diarrhea.

  18. Lactose intolerance • Usually not seen in < 6 years old children. The % L.I. people increases with age (highest among the elderly). • Low among Western European Americans (6-25%), high in other populations (50-75%). • Suggest that production of lactase is under genetic control.

  19. Dealing with lactose intolerance • Reduce lactose by fermentation (yogurt, buttermilk etc.) • Add lactase to lactose containing foods just before consuming (or consume lactase). • Novel technology: add live yogurt cultures to refrigerated milk, the bacteria release lactase upon reaching the small intestine. • Reduce lactose to lactitol (hydrogenation with H2), or isomerize in alkaline to lactulose (keto sugar). Lactitol and lactulose are not absorbed by small intestine and are fermented to lactic and acetic acids. The water attracting properties of these acids soften stools and facilitate bowel function.

  20. Sucrose • Sucrose structure: an exception to the general rule for oligo- and polysaccharides, glycosyl units are linked “head-to-head” (reducing end to reducing end” • Non-reducing sugar: CHO- of D-glucosyl unit and C=O of D-fructosyl unit are in glysosidic bond, no reducing end. • The glycosidic bond is high energy, unstable (partly due to the strained fructofuranosyl ring.

  21. Sucrose • As a result, sucrose is easily hydrolyzed in very dilute acid or enzymes: H+ Sucrose Glucose + Fructose invertase (yeast, bacteria) or intestinal sucrase invert sugar (equimolar mixture of D-glucose and D-fructose) []D= +66.5 []D= -33.3 invertase:-D-fructofuranosidases, leaves O atom with D-glucose sucrase: -D-glucosidase, leaves O atom with D-fructose

  22. Sucrose and invertase sucrase: leaves oxygen atom with D-fructose invertase: leaves oxygen atom with D-glucose

  23. Sucrose sources • Sucrose is synthesized mainly in plant leaves, then transported throughout the plant, and stored in stems, roots ot tubers. • Sources: sugar cane and sugar beet Processing steps involve: crushing/extracting, treating with lime, heating, filtration and crystallization and refining treatments (for decolorizing and recrystallizing)

  24. Sucrose properties and uses • Sucrose is very soluble in water (67g per 100 g solution at 20C), can form highly concentrated solutions (syrups, honey). • Uses: sweetener, preservative, humectant • Cryoprotectant function: as water crystallizes, [sucrose] increases freezing point decreases viscosity of the remaining solution increases. Eventually, the liquid phase solidifies as a glass (vitrification). This explains how some carbohydrates can protect against dehydration via crystallization) that destroy structure and texture by freezing.

  25. Sucrose structure in solution & crystals

  26. Sucrose Derivatives: Sucrose Esters • Sucrose molecule has a very rich potential: • non-reducing, stable,pure, cheap polyol • various reactions: oxidation, reduction, esterification etc. • Sucrose esters: low esterification (1-3 fatty acids, e.g. stearic acid)  surfactants (emulsifiers) fully acetylated sucrose (sucrose octaacetate)  very bitter, use to denature ethanol with long chain fatty acids (8-12 carbon atoms), 6-8 fatty acids (hexa-, hepta- and octa-ester)  not metabolized or absorbed e.g. OLESTRA (low-calorie fat substitute)

  27. Structure of sucrose polyesters • Esssential structural characteristics: • apolar part: fatty acids • polar part: non-esterified hydroxides of sucrose • and glycerol (sucroglycerides) •  different hydrophilic-lipophilic balance (HLB value)

  28. Sucralose • Chlorinated sucrose with a D-galactopyranosyl unit in place of the normal D-glucopyranosyl unit.

  29. Sucralose 600 x sweeter than sucrose, good taste quality Adequate water solubility Not hydrolyzed in small intestine 60 x more stable to acid than sucrose Approved for use in the US since 1998 • Uses: tabletop sweetener, beverages, baked goods, chewing gums, dry mixes, fruits spreads, frozen desserts.

  30. Isomaltulose

  31. Isomaltulose (Isomalt, Palatinose) • Prepared by enzyme-catalyzed transfer of the glycosidic linkage from O-2 to O-6 in the D-fructopyranosyl unit. • Enzyme is produced by Protaminobacter rubrum. • ½ sweetness of sucrose. • Uses (in Europe): noncariogenic candies, specialty chocolate, chewing gums, cookies

  32. Isomaltitol(Palatinit) • Hydrogenation of isomaltulose with hydrogen and a catalyst  Palatinit • Crystalline, about 45% as sweet as sucrose. GPM:-D-Glc-(16)-D-manitol GPS:-D-Glc-(16)-D-sorbitol

  33. Leucrose • Leucrose is a reducing disaccharide • Produced by Leuconostoc mesenteroides • 50% as sweet as sucrose

  34. Kestose and Neosugar Kestose (GF2) Fructosefuranosyl nystose (GF4) Nystose (GF3)

  35. Kestose and Neosugar • Preparation of kestose and neosugar: A concentrated solution of • sucrose is treated with invertase or a fungal transferase. • This causes the transfer of D-fructosyl units onto sucrose. • 50% as sweet as sucrose. • Non-cariogenic, approved for use in Japan.

  36. Inulin • Structure: condensation of hundred units of • D-fructose, by means of -21 bonds,with • a few D-glucose units at the end. • Inulin properties: • - its gelling capacity can improve emulsion stability - non-digestibility, behaves as dietary fiber, and is hydrolyzed by bacteria in the colon (bifidobacteria & lactobacilli) - low caloric value (4-10 kJ/g) Uses: as fat substitute and dietary fiber for low-calorie foods (40% inulin +60% water, with high shear  network trapping water molecules, stabilizing emulsions) n-1

  37. Trehalose

  38. Trehalose • Found in animals and plants that are known as anhydrobiotic, (survive drying and freezing, e.g. frogs, desert plants, insects). Trehalose molecule fits into the gap in polymer structure vacated by water and maintains the necessary H- bonds that support the proetin and membrane structure. • Extraction of trehalose from plant/animal tissues is impractical. It’s now feasible to hydrolyze starch to trehalose by fermentation with yeasts, bacteria. • Commercial trehalose syrups are being used to preserved dried and frozen foods. • Current issue: is trehalose really a better stabilizer?

  39. Rafinose and Stachyose • Mostly from beans and other legumes, sugar beet extract • Cause flatulence

  40. Rafinose

More Related