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Food Chemistry 1 > C1. Intro > Flashcards

C1. Intro Flashcards

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1
Q

Fundamental units of carbs? why?
- general formula?

A
  • monosaccharides (simple sugars) because not hydrolyzed by acid to form a smaller unit
  • C_x(H_2O)_x –> corresponds to hydrates of carbon
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2
Q

most common monosacs have what molecular formula?
- 3 monosacs?
- exist primarily in what form?

A
  • C6H12O6
  • glucose, galactose, fructose
  • cyclized form
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3
Q

disacs consits of what linked by what bond?
- 3 disaccharides: from what? + characteristic

A
  • 2 simple sugars linked by covalent glycosidic bond (ether linkage R - O - R)
  • maltose: glucose + glucose –> common enzymatic hydrolysis product of starch
  • sucrose: glucose + fructose –> common table sugar
  • lactose: glucose + galactose –> major sugar in cow’s milk
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4
Q

what are oligosaccharides?
- 2 examples –> formed of what?

A
  • 3 to 10 monosaccharides linked together by glycosidic bonds
  • raffinose (trisaccharide): galactose, glucose and fructose
  • stachyose (tetrasaccharide): glucose, fructose and 2 galactose
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5
Q

polysaccharides are what?
- 5 examples

A
  • polymers of monosacs that have a chain length > 10 units
  • starch, cellulose, glycogen, pectin and xanthan gum
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6
Q

4 common roles of carbs in living systems? + from what type of carb?

A
  1. energy source in seeds: starch for germination
  2. structural component: cellulose and hemicellulose (plant cell wall)
  3. ready supply of energy: mono and disacs
  4. short term energy supply for muscles: glycogen
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7
Q

3 functionality of mono and disacs in food?

A
  1. sweetening agents
  2. coloring agents (caramel colour)
  3. production of flavors (caramelization/Maillard reaction)
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8
Q

7 functionality of polysacs in food?

A
  1. thickening agents
  2. gelling agents
  3. emulsion stabilizers
  4. water holding/binding agents
  5. anticaking agents
  6. producing edible films
  7. encapsulate flavors
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9
Q
  • how many carbons do monosacs have? range
  • 2 functional groups of monosac in their linear form?
A
  • C3H6O3 to C7H14O7
  • alcohol group + ketone (C2) OR aldehyde group (C1)
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10
Q

which compound is used as reference compound to determine __-___ isomerism?
- how?
- vs other sugars?

A

glyceraldehyde!
- D-L isomerism
- aldehyde group on top, OH to right = D-isomer vs OH to left = L-isomer
- other sugars: carboxylic group on top (C1), OH on C at (n-1) position determines D or L

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11
Q

what are epimers?

A

optical isomers involving asymmetric carbons other than the carbon at the n-1 position
(ie only difference at C2 for a 6 carbon monosac)

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12
Q

isomers can be generated through _______ or ________ _________

A

acid or base catalysis

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13
Q

describe number of carbon + ketone vs aldehyde
- ketohexose
- aldohexose
- aldopentose

A
  • ketohexose: C6 ketone
  • aldohexose: C6 aldehyde
  • aldopentose: C5 aldehyde
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14
Q

cyclization is due to the formation of internal _______ and _________
- reactions are intra/intermolecular? explain

A
  • hemiacetals
  • hemiketals
  • intramolecular: alcohol group attacks aldehyde or ketone group of the same molecule
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15
Q
  • hemiacetal formation of glucose –> what ring?
  • hemiketal formation in fructose –> what ring?
  • which is more stable?
A
  • hemiacetal –> pyranose
  • hemiketal –> furanose ring
  • pyranose is most stable!
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16
Q

cyclization results in an additional __________ carbon at the ___ position, termed ________ carbon, leading to 2 optical isomers, termed ________
- what are the 2 isomers?

A
  • asymmetrical carbon at C1 position, termed anomeric carbon
  • anomers!
  • alpha form: OH group at anomeric carbon is on opposite side of ring as C6
  • beta form: OH group at anomeric carbon is on same side as C6
17
Q

3 different projections/conformation for monosacs?

A
  • Fischer projection (linear/planar)
  • Haworth projection (hexagone)
  • chair conformation
18
Q

in solution there is a _________ equilibrium between which 3 forms?
- how can it be observed?

A
  • dynamic equilibrium!
  • a, b and open chain
19
Q

how can dynamic equilibrium between a, b and open form be observed?
- when pure a-D-glucopyranose is dissolved in water, ______ ______ starts are ____° and gradually changes to ___°
- when pure b-form dissolved in water, _______ _______ starts at ___ and gradually changes to ____°
- this phenomenon is termed what?

A
  • observed by following the optical rotation of plane-polarized light by a solution of sugar
  • alpha: optical rotation starts as 112° –> 53°
  • alpha: optical rotation starts as 19° –> 53°
  • mutarotation
20
Q

mutarotation is the result of (2)
- equilibrium between a, b and open chain of glucopyranose? (percentages)
- vs of fructose?

A
  1. cyclic form opening up
  2. recyclizing, coming to equilibrium with its anomer
    - 62% b-D-glucopyranose + 37% a-D-glucopyranose + 1% open chain form
    - fructose –> equilibrium is more complicated bc cyclization via formation of hemiketal can produce furanose OR pyranose
21
Q

aldehyde group present on ________ has strong what? explain

A
  • aldoses has strong reducing power
  • aldehydes are capable of reducing metal ions (oxidation-reduction reaction that converts aldehyde to a carboxylic acid)
22
Q

as a group, monosacs are generally termed ________ sugars and can be tested for and quantified by specific what reactions?
- most common test? involves what?

A
  • reducing sugars
  • by oxidation/reduction reactions
  • Fehling’s test –> reduction of Cu(II) (blue) in form of copper tartrate to Cu(I) oxide (reddish brown precipitate)
23
Q

Fehling’s reagent only reacts with what?
- accordingly, only reacts with what form of monosac?
- although only _% of sugar is in that form, when that form is depleted, what happens?

A
  • free aldehyde groups
  • open-chain form
  • 1% of sugar is in open-chain form –> when open-chain form is depleted by above reaction, it is replenished by opening of the ring forms (with which it is in equilibrium)
24
Q

is fructose a reducing sugar?

A

even if it is a ketose sugar and has no aldehyde group, it is still a reducing sugar
- because fructose is converted into glucose (ketose –> aldose) (enolization) –> glucose can then react with Fehling’s solution

25
Q

what is the intermediate between conversion of aldose to ketose?

A

endiol (deprotonierte form)

26
Q

when is reducing power of a sugar lost?

A

when OH at anomeric carbon of cyclic form is covalently bonded to another group –> prevents ring from opening
(conversion to open-chain form requires that an OH group bound to anomeric carbon to revert back to an aldehyde group)

27
Q

maltose vs sucrose –> which is non-reducing vs reducing?
- why?
- what linkage?

A
  • maltose = reducing –> 2nd glucose is not involved in the glycosidic bond –> ring opening can occur at one end of molecule –> but only has 1/2 reducing power of glucose bc one of the 2 anomeric carbons is used in glycosidic bond
  • maltose = a-1-4 glycosidic linkage
  • sucrose = not reducing –> both anomeric carbons (C1 and C2 of fructose) are tied up in the glycosidic bond, so ring opening cannot occur
  • sucrose = a-1-2 glycosidic linkage

Food Chemistry 1 (22 decks)

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