Foodchem Lecture 16

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  1. What is the general formula for a carbohydrate?
  2. What is the basic unit of a carbohydrate?
    Simple sugar or monosaccharide
  3. What does the name 'simple sugar' mean?
    Will not undergo acid hydrolysis to form smaller units
  4. What are 2 common examples for simple sugars?
    D-glucose and D-fructose
  5. Both glucose and fructose also exist as which other structure of compounds?
  6. What is the definition of a dissacharide?
    2 simple sugars linked by a covalent glycosidic bond
  7. What is a covalent glycosidic bond?
    A specific type of ther linkage (R-O-R) between the OH on the anomeric carbon of a sugar to any other alcohol (usually another sugar molecule)
  8. Where does sucrose come from?
    • Sugar cane
    • Sugar beet
  9. What is sucrose made up of?
    Glucose and fructose
  10. What is lactose made up of?
    Glucose and galactose
  11. Where does maltose come from?
    Starch enzymatic hydrolysis
  12. What is maltose made up of?
    2 glucose molecules
  13. What is the definition of an oligosaccharide?
    3-10 monosaccharides linked together
  14. What is raffinose made up of?
    Trisaccharide of galactose, glucose and fructose
  15. What is stachyose made up of?
    A tetrassacharide of glucose, fructose, and galactose
  16. What is a common use of oligosaccharides?
    Used as prebiotics, or promoters of desirable intestinal flora
  17. What are 2 examples of prebiotics?
    • Oligofructose (2-8) units
    • Inulin (9-64) units
  18. What are polysaccharides?
    • Longer chain length polymers, found in nature
    • A variety have food applications
  19. What are some examples of polysaccharides?
    • Starch
    • Cellulose
    • Glycogen
    • Pecton
    • Xanthan gum
  20. What is the role of carbohydrates in nature?
    • Energy sources as starch for germination of seeds
    • Structural components as cellulose and hemicellulose in plants (including trees)
    • Ready supply of energy as mono and disaccharides
    • Short term supply of energy in muscles (as glycogen)
  21. What are mono and disaccharides used for in food functionality?
    • Sweetening agents
    • Coloring agents (caramel color)
    • Viscosity enhancers
    • Flavor production (caramellization, Maillard rxn)
    • Flavor carriers (plated flavors, like vanilla on sugar)
  22. What are oligosaccharides used for in food functionality?
  23. What are polysaccharides used for in food fuctionality?
    • Thickening and/or gelling agents
    • Emulsion stabilizers
    • Water holding/binding agents
    • Production of edible films
    • Encapsulation of flavors
  24. How are carbon chains numbered in sugars?
    From the carbonyl end down
  25. The C3 to C7 portions of monosaccharides are known as what?
    Polyhydric alcohols
  26. What is the carbonyl group of a monosaccharide?
    An aldehyde or ketone
  27. What is the simplest monosaccharide?
  28. What is the absolute reference to determine D or L configuration of sugars?
  29. Why was glyceraldehyde chosen to be the reference compound for determining D and L configuration?
    • It has only one chiral carbon
    • Most sugars have more than 1 chiral carbon
    • The D or L designation of sugars is based solely on the configuration of the n-1 carbon, i.e. on the carbon one before last, when counting from the carbonyl group
  30. What are enantiomers?
    Mirror images, or any D vs. L configuration of the same sugar
  31. What are epimers?
    • Changes at any carbon other than the n-1 carbon, for example for the same molecular formula
    • (As at C2 in D glucose vs D mannose)
    • All epimers are considered different sugars
  32. How are monosaccharides classified?
    May be classified as to chain length and functional group type
  33. What are ketoses?
    6C ketones, like fructose
  34. What are aldohexoses?
    6C aldehydes, like glucose
  35. How are monosaccharides generally represented for simplicity?
    • As linear molecules
    • In reality (both in crystals and, predominantly, in solution) they are cyclic
  36. What do sugars form to become cycles?
    Hemiacetals and hemiketals
  37. How does the chair form of beta glucose form?
    • The double bond oxygen becomes an alcohol
    • The alcohol oxygen becomes an ether
    • C1 becomes the center of a hemiacetal (A carbon wtih both an ether and alcohol on the same carbon)
  38. How is cycle closure catalyzed?
    By an acid
  39. What is the anomeric carbon?
    The new chiral carbon formed at C1 where the cycle closes
  40. What are the alpha and beta forms of monosaccharides called?
  41. What happens when a monosaccharide is dissolved in solution?
    A dynamic equilibrium is set up between the 3 possible forms of the monosaccharide (open chain, alpha anomer, beta anomer)
  42. What is mutarotation?
    Changes in optical rotation, when a pure type of sugar is dissolved in water
  43. What does mutarotation result from?
    • the opening of one form, coming to equilibrium with the opposite anomer via the open chain form
    • it may crystallize into the 5 member ring or into the 6 member ring
  44. What is the breakdown of glucose equilibria?
    • 62% alpha pyranose
    • 37% beta byranose
    • <1% open chain
  45. What is fructos mutarotation like?
    A 5 member ring (furanose)
  46. In general, 6 carbon aldoses tend to form which cyclic rings in mutarotation?
    Pyranose rings
  47. In general, 6 carbon ketoses tend to form which cyclic rings in mutarotation?
    Furanose rings
  48. The crystalline form of simple sugars is always what?
  49. The aldehyde group on aldose is a strong agent for what?
  50. All monosaccharides are which kinds of sugars?
    Reducing sugars
  51. What is a reducing sugar?
    Capable of reducing metal ions and being oxidized to carboxylic acids (redox reaction)
  52. What does Fehling's reagent react with?
    Only reacts with free aldehyde groups (showing presence of reducing sugars)
  53. Why is fructose considered a reducing sugar?
    • Fructose is a ketose, thus no free aldehyde group
    • Still considered a reducing sugar since it goes through a rearrangement when in basic conditions (enolization)
  54. How is reducing power of a sugar lost?
    • If the OH on the anomeric C is covalently bound to another group
    • The glycosidic link is formed, and the cycle cannot open up anymore, thus no free aldehyde can be regenerated
  55. Is sucrose a reducing sugar?
    NO - due to its glycosidic bond, where both anomeric carbons are tied up in making the bond
  56. Is maltose a reducing sugar?
  57. Is lactose a reducing sugar?
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Foodchem Lecture 16
2012-04-22 19:20:05
Foodchem Lecture 16

Foodchem Lecture 16
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