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Food Chemistry 1 > C2. Dehydration, browning rxns, caramelization, sweetness > Flashcards

C2. Dehydration, browning rxns, caramelization, sweetness Flashcards

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1
Q

Dehydration reactions are significant to food industry bc they are the basis of (2) reactions

A
  • Caramelization (color and flavor)
  • Maillard reaction
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2
Q

best conditions (temp + pH) for dehydration reactions? but can still happen at ?

A
  • concentrated sugar solutions are heated at temps above 130°C and under very acidic conditions (pH < 2.2), dehydration reactions become prevalent
  • can still happen, but very slowly at temps below 100°C and in dilute solutions
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3
Q

as water evaporates from solution (dehydration reaction), 2 things take place, leading to breakdown of what into what?

A
  • molecular (internal) dehydration and oxidative fission take place
  • leading to breakdown of carbon chain into smaller units (flavor compounds)
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4
Q

2 ways that water can be eliminated from sugar molecules?
- which one is more predominant?

A
  1. loss of water from 2 sugar molecules by reaction of their hydroxyl groups (R-OH + OH-R –> ROR (polymer) + H2O) –> results in random polymerization (generally not predominant reaction)
  2. elimination of water from within a sugar molecule, leading to formation of highly unsaturated ring structures
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5
Q

common intermediate formed during caramelization reactions by dehydration is ?

A

hydroxymethylfurfural (HMF)

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6
Q

fragmentation reactions of highly unsaturated ring structures produce various compounds (3 characteristics)
- 3 examples

A
  • low-molecular weight
  • unsaturated
  • reactive
  • acetol, diacetyl, acetoin
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7
Q

many of highly unsaturated ring structures and their breakdown products (3) can _____________

A

breakdown products like short-chain aldehydes, ketones, carboxylic acids)
- can polymerize

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8
Q

extensive dehydration reactions eventually lead to formation of an amorphous, _________ ________ pigment called _________

A
  • charged brown pigment
  • caramel
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9
Q

browning reactions can be classified into 2 categories:

A
  1. enzymatic (oxidative) browning: when fruits/veggies turn brown when left on table
  2. non-oxidative browning/non-enzymatic browning
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10
Q

enzymatic/oxidative browning:
- related to carbohydrates?
- associated with browning of ________ tissues
- what enzymes oxidizes what into what?

A
  • not related to carbs!
  • plant tissues
  • most commonly polyphenol oxidase (PPO) oxidizes mono or dihydroxy phenols into quinones
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11
Q

quinones are quite reactive/unreactive and can react ___-_________ to _________ into a ________ pigment

A
  • reactive
  • non-enzymatically to polymerize into a brown pigment
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12
Q

what other enzymes (apart from polyphenol oxidase) are indirectly associated with browning? (2)
- these can produce/supply reactive _______ compounds that can undergo ___-_________ _________

A
  • ascorbic acid oxidase and lipoxygenase
  • carbonyl compounds –> non-enzymatic browning
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13
Q

2 types of non-oxidative browning
- caramelization vs Maillard?

A
  1. sugar-sugar reactions (caramelization)
  2. sugar-amine reactions (Maillard reactions)
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14
Q

caramelization reactions occurs when any concentrated sugar solution is ________

A

heated

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15
Q

caramelization is used commercially to produce (2)
- each is generally made from what?

A
  • caramel flavor/syrup –> made from concentrated sucrose solutions
  • caramel color –> generally made from glucose syrup (more reducing)
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16
Q

which 2 reactions produce what type of polymers that are very dark in color? (high tinctorial power)

A
  • dehydration and polymerization
  • produce high-molecular weight water-soluble polymers
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17
Q

caramel colors produced in what foods (5)

A

baking, beer, soft drinks, whiskey, soy sauce…

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18
Q

Maillard reaction involves reaction of what with what (generally (2))

A
  • of reducing sugars with primary amines (generally amino acids and proteins: free amino groups on side chains (ie: e-amino group of lysine))
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19
Q

which aromas are associated with Maillard reactions? (4 ish)

A
  1. coffee flavor, color and aroma (formed during roasting)
  2. popcorn aroma/flavor
  3. roasted peanuts, cashews
  4. baked bread aroma
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20
Q

condensation of primary amine and reducing sugar form a _______ ______ –> followed by formation of an _________ compound

A
  • Schiff base
  • Amadori compound
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21
Q

what is a key intermediate in Maillard reaction, comparable to _____ in caramelization

A

Amadori compound!
- comparable to HMF

22
Q

converting Schiff base to amadori compound is termed what?

A

amadori rearrangement

23
Q

can the amadori compound lose water from within the molecule?

A

yes

24
Q

at higher temps, what are the major reactions following amadori rearrangement?
- key difference with caramelization?

A

dehydration and fragmentation (much like caramelization)
- key difference: there is an amine group attached to sugar –> end products tend to contain nitrogen in their structure

25
Q

fragmentation produces short/long chain unsat/sat _______ and _______ compounds that can ________ and/or be released as ________ into the environment (aroma)

A
  • short-chain unsat carbonyl and amino compounds
  • can polymerize or be released as volatiles
26
Q

net result of reactions of amadori compound? (2)

A

brown pigments and volatile compounds containing nitrogen are formed

27
Q

Strecker degradation is a subcomponent of the _________ reaction
- involves reaction of what with what produced by either _______ or _________ reactions

A
  • Maillard reactions
  • reaction of free amino aicds with the dicarbonyl intermediates produced by Maillard or caramelization reactions
28
Q

products formed during strecker degradation? (4) which are compounds that contribute to the characteristic aroma of ________ foods

A
  • CO2, ammonia, formaldehyde and pyrazines
  • roasted foods
29
Q

common strecker aldehydes? (3 + what kind of aroma)

A
  • ethanal –> fruity, sweet aroma
  • methylpropanal (malty)
  • 2-phenylethanal (flowery, honey like aroma)
30
Q

condensation of 2 _________ may yield pyrazine derivatives that are also powerful ______ compounds

A
  • aminoketones
  • aroma
31
Q

what reaction is used commercially to produce artificial flavor compounds?
- how?
- how are these flavor compounds isolated?

A
  • Strecker degradation
  • reacting sugars and selected amino acids under proper conditions –> can produce variety of flavors such as chocolate, bread, caramel, almond
  • by distillation and then added to food products
32
Q

in summary, which 3 reactions represent important group of reactions associated with food color and flavor?

A
  • caramelization
  • Maillard reaction
  • Strecker degradation
33
Q

why is evaluation of sweetness quite difficult? (2)
- how to evaluate?

A
  • because it is a subjective response + cannot be measured objectively by an instrument
  • sensory evaluation! by controling as many variables as possible and using statistical methods to remove individual variations
34
Q

which sugar is used as reference for sweetness? why?

A

sucrose! because it is the most abundant

35
Q

rank relative sweetness from lowest to sweetest:
- xylose
- lactose
- invert sugar
- sucrose
- glucose
- maltose
- fructose

A
  • lactose 39
  • maltose 46
  • invert sugar 65
  • xylose 67
  • glucose 69
  • sucrose 100
  • fructose 114
36
Q

what is an invert sugar?

A

sucrose hydrolyzed to a mixture of glucose and fructose –> optical rotation is inverted (ie from 100 to -100)

37
Q

3 variables involved in how sweetness if perceived
1. increase temp = decrease/increase sweetness –> attributed to what?
2. some people can differentiate ______ of sweetness (vs _______ in sweetness)
3. relative sweetness of sugar is changes in presence of (4)

A
  1. increase temp = decrease sweetness –> attributed to change in relative concentrations of open-chain, a, and b forms which differ in sweetness
  2. type of sweetness (vs difference in sweetness) while others can’t…
  3. salts, acids, others sugars, and a host of other components (ie alcohol tend to heighten sweetness)
38
Q

what is the synergistic effect of sugars?

A

sugars can become sweeter when mixed together than when tasted separately

39
Q

sweetening power is related to sugar __________

A

solubility (proportional ish to sweetness determined by sensory eval ishh)

40
Q

when is solubility a very important criterion? (2 ex)

A

when high sugar concentrations are required to inhibit microbial growth (jams, jellies)

41
Q

what happens if solubility of sugar is too low?

A

sugar can crystallize, making the product texture grainy

42
Q

limitations in solubility may be encountered in sweetened condensed or evaporated milk and ice cream, owing to what?

A

relatively low solubility of lactose (milk sugar)

43
Q

common method to avoid sugar crystallization?

A

mix 2 sugars together –> inhibits their crystallization

44
Q

sugars can also be used as a preservative against ______ and ________ _______, and to help in formation of _______ _____ in jams and jellies
- how do sugars do that?

A
  • mold and bacterial growth
  • pectin gels
  • sugars effectively bind water, making it unavailable for microorganisms due to the lowering of water activity of the system
45
Q

other uses of sugars:
- to facilitate _______ and ______ production during baking (Maillard reaction) –> if not desired, minimize by using ________
- to help ______ development in meat curing –> _________ sugars prevent ________ of meat pigments
- as (3)

A
  • browning and flavor production –> minimize browning by using sucrose
  • to help color development –> reducing sugars prevent oxidation of meat pigments
  • as humectants, flavor binding agents and viscosity enhancers
46
Q

sugar alcohols are used extensively in food industry as (2)

A
  • bulking agents and viscosity enhancers in artificially sweetened products to provide “body”
  • as water-binding agents to plasticize intermediate moisture foods and reduce the water activity of food system without adding excessive sweetness
47
Q

sugar alcohols are absorbed by _________ diffusion, thereby contributing to more/fewer calories than sugars
- they are greatly/poorly metabolized by microbial flora in mouth –> do/do not contribute to dental caries (which are caused how?)

A
  • passive
  • fewer calories than sugars
  • poorly metabolized –> do not contribute to caries
  • caused by acids produced by microflora form fermentation of sugars
48
Q

most sugar alcohols (2 ex) are more/not as sweet as sugars
- except which one? which has comparable sweetness to _________

A
  • sorbitol and mannitol
  • not as sweet as sugars
  • xylitol = exception –> comparable to sweetness of sucrose
49
Q

xylitol is produced from what?
- how is it produced (3)

A
  • produced from xylan, a polymer of xylose which can be widely found in nature (birch tree chips, almond and pecan shells, corn cobs)
  • xylan is hydrolyzed to xylose and hydrogenated using a nickel catalyst to produce xylitol
    OR yeasts convert xylose to xylitol by fermentation
    OR enzymatic conversion of glucose to xylitol
50
Q

difference between D-xylose and D-xylitol?

A
  • xylose –> 5C –> OH on one end and COOH on one end = aldehyde
  • xylitol –> 5C –> OH on both ends

Food Chemistry 1 (22 decks)

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