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The flashcards below were created by user
Morgan.liberatore
on FreezingBlue Flashcards.
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In what conditions are sugars relatively stable?
Relatively stable in water at neutral pH, at room temperature
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What happens if sugars are inw ater outside of the neutral range (on either side) or with strong heating?
- Elonization may take place: Double bonds become 'mobile'; monosaccharides may change from one form to another
- Acid or base catalysed, with heat speeding up the overall rate
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What is Elonization?
double bonds become 'mobile'; monosaccharides may change from one from to another
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What is the general reaction of enolization?
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What is an alkaline reaction of sugars?
- Starting with concentrated solution of pure glucose, regluzed under alkaline conditions
- At the end, a variety of different epimers
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What are the steps for aldose to ketose conversion of enolization with base?
- 1. Remove the alpha proton
- 2. reprotonate on O
- 3. Reprotonate the O o C2
- 4. Reporonater o C1
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What does base catalyzed enolization induce?
- Induces 'wandering' of the double bond
- Epimerization of both aldo and keto sugars
- Conversio from aldoses to ketoses
- Results in complex misture, even when starting with a single sugar
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Is base catalyzed enolizatio reversible?
Only if temperature is not too high
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What happens in base catalyzed enolization if temperature is high?
- Water evaporates
- Dehydration and oxidative scission
- Carbohydrates breakdown into smaller units
- flavors
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What is the general reaction of sugars in acid catalysis?
- Results similar to base catalysis, but overall tendency is conversion of ketoses to aldoses
- ORganic acids, pH range 3-6
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What is the pH range of organic acids?
pH 3-6
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What happens in dehydration reactions of sugars?
- After loos of free wter, sugar molecules will lose water from within their molecular structure
- Basis for carmellizatio (flavor and color) as well as Maillard reaction
- Common intermediate is HMF (hydroxymethyl furfural)
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What is a common intermediate of dehydration reactions?
HMF- hydroxymethyl furfural
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What is the basis for carmellization and Maillard reactions?
Dehydration reactions
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What is the general procedure of sugar dehydration starting with 70% glucose solution?
- Free water lost, concentration goes up, as well as temperature
- Water eliminated internlly: 2 possible pathways
- pH will affect reaction
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What are the 2 possible pathways of water loss in a sugar dehydration reaction?
- Loss of H2O between 2 glucose units (random dimerization; not predominant)
- Loss of H2o from one sugar molecule (highly reactive HMF)
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How does pH affect sugar dehydration reactions?
Low pH minimizes enolization prior to dehydration
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How is carmel formed?
- Many unsaturated cyclic products and their breakdown products, which may polymerize via the aldol condensation reaction
- Formation of amorphous brown pigments called carmel color
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Which reaction is prefered under basic conditions?
- Enolization reaction is more prevalent
- dehydration limited in early stages of the reaction
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What are the end products under basic conditions?
- Fragmentation of sugar molecule prevalent
- End products tend to be acidic
- If not properly buffered, will eventally promote dehydration
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Do acidic or basic conditions yield brown colors of pigments?
Both basic and acidic conditions yield brown colors or pigments
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What is browning often associated with?
Headed products or natural decay processes
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What are the two categories of browning reactions?
- Oxidative or enzymatic browning
- Non-oxidative of nonenzymatic browning
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What is enzymative browning?
- Associated with plant tissue browning
- Enzyme: as polyphenol oxidase
- Oxidation of hydroxyphenols into quinones
- Quinones may react further and eventually polymerizeinto brown compounds
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What is the end product of non-enzymatic browning?
End product attributes depend on type of sugar and reaction conditions
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What is the difference between carmellization and maillard reactions?
- Carmellization= sugar-sugar
- Maillard reactions= sugar-amine
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How are carmel flavors formed from glucose?
- From concentrated sucrose solution:
- Hydrolysis to glycose and fructose
- Ring opening: equilibration of both anomers
- Enolization and epimerization
- Dehydration: some polymerization
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What is the result of polymerization of unsaturated and reactive carbonyl compounds in a carmellization reaction?
Viscous brown solution with typical carmel flavors
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What happens to a carmelization reaction upon cooling?
May crystallize. or form amorphous candy
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How is carmel color formed from a glucose syrup?
- Heat treatment with dilute H2SO4
- Acid partially neutralized with NH3 and basic salts as the reaction progresses
- Conditions which promote sugar fragmentation and prevent development of bitterness
- Ammonia has double role of neutralizing agent, and cross linker promoting polymerization
- Few sugars are left intact
- Dehydration and polymerization are main reaction
- High molecular weight products
- Water soluble
- Very dark--> high tinctorial power
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What is the role of H2SO4 in carmel color production?
- Sulfite plays a role in reducing the isoelectric point of the polymer formed
- Polymers with charged SO3- groups incorporated: remain charged at pH as low as 2.5
- Carmel polymers will thus remain in solution in the low pHs encountered in carboanted beverages
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What do maillard reactions require?
Reducing sugars and primary amines
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What are some examples of miallard reactions?
- Coffee
- Popcorn
- Roasted peanuts
- Baked bread aroma
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What can the maillard reaction be considered with respect to carmellization?
The maillard rection can be considered a nitrogen version of the carmellization reaction
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How are maillard reactions used to produce flavor constituents reminiscent of specific products?
- Often by exploiting a particular sub-reaction called strecker degredation:
- reactio of free amino acids with dicarbonyl intermediates coming from either the maillard reaction of from carmellization
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What is strecker degredation?
Reaction of fre amino acids with dicarbonyl intermediates coming from either the maillard reaction of from carmellization
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What are produced from strecker reactions?
A wide variety of 'artificial' flavor/aroma compounds may be produced, by careful selection of sugars and amino acids
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What is the downside of maillard reaction?
- Acrylamide formation- considered a compound of high concern
- Present in french fries, potato chips, coffee, prune juice
- Asparagine+carbs: natural pathway for prouction of acrylamide
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What is the reference sugar for relative sweetness?
sucrose?
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What is the general order of relatie sweetness?
- Lactose-39
- Maltose-46
- Invert sugar-65
- Xylose- 67
- Glucose-69
- Sucrose-100
- Fructose 114
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How does temperature affect percieved sweentess?
- Sweetness tends to decrease with increased temperature
- Change in relative concentration of the various forms
- Open chain or cyclic alpha and beta
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What are some variables ins weetness perception?
- Tends to decrease with increased temperature
- Personal perception: distinguishing sucrose from glucose for example
- Presence of other components (salt, acids, alcohol)
- Synergy- Mixtures of different sugars may taste sweeter than the sum of individuals
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What is the best way to evaluate sweentess?
Taste panels
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When are sugar solubilities important?
Important when making jams and jellies, where high concentrations are required to inhibit microbial growth (lower water activity)
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What happens if solubility is too low?
If solubility os low, sugar may crystallize out- textyre will be gainy or sandy
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How is crystallization avoided?
- Crystallization may be avoided by mixing two sugars together
- Crystal lattie much more difficult to form where more than one sugar is present
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How is inversion acquired?
Inversion may be enzymatic, or by heating in the presenc of ascorbic acid
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How does caramilk avoid crystallization?
Uses a mixture of sugrose, glucose and fructose
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What are some other uses for solubility of sugars?
- Coloor development in cured meats
- Reducing conditions (reducing sugars) prevent oxidation of meat pigments
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What is a sugar alcohol?
- Sugar here the carbonyl group has been reduced to an alcohol
- Similar to lipid hydrogenation
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Where are sugar acohols used?
- Reduced caloric contribution; ot as sweet as sugars
- Also as water binding agent with reduced sweetnening effet
- Humectnat to bind water and plasticize intermediate moisture foods
- Bulking agend and viscosity enhancers with artificial sweeteners
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What are some common sugar alcohols?
- Glucitol (relative sweetness= 51)
- Mannitol (relative sweetness= 54)
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What is xylitol?
A very sweet sugar alcohol
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What is xylitol similar to in terms of sweetness?
Similar to sucrose in terms of sweetness
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What is important about xylitol?
- Poorly metabolizxed y microbial flora in the mouth
- Helps prevent dental caries
- Unique in that it provides both a sweetening sensation and cooling sensation
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What is the sugar form of xylitol?
xylose
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How is xylose naturaly found?
- Widely foun d in nature as xylan, a polymer of xylose
- Plant sources: birch tree chips, almont and pecan shells, corn cobs
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How is xylitol produced?
Xylan hydrolyzed to xylose; xylose hydrogenated in xylitol
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How is xylitol produced?
- Xylitol may be produced by action of yeast: Fermenting xylose into xylitol
- Or enzymativ conversion of glucose to xylitol
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How is xylitol used in canada?
Only in chewing gum in canada
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