Carbohydrates I Flashcards
The fundamental units of carbohydrates are __________
monosaccharides
What is the general formula of monosaccharides?
Cx(H2O)x
Monosaccharides are the fundamental units because they are not _______ by ________ to form a smaller unit.
hydrolyzed
acid
The most common monosaccharides have the molecular formula: ________
C6H12O6
Monosaccharides exist primarily in the ________ form
cyclized
What are the three monosaccharides?
- Glucose
- Galactose
- Fructose
Disaccharides consist of two sugars linked by a covalent _________
glycosidic bond
_______ is the common enzymatic hydrolysis product of starch
Maltose
________ is the common table sugar
Sucrose
_______ is the major sugar in cow’s milk
Lactose
________ consist of 3 to 10 monosaccharides linked together by glycosidic bonds
Oligosaccharides
_________ is a trisaccharide formed of galactose, glucose, and fructose
Raffinose
_________ is a tetrasaccharide, formed of glucose, fructose, and two galactose
Stachyose
glucose
fructose
two galactose
When the chain length of an oligosaccharide exceeds __ units, the polymers are termed _________
10
polysaccharides
________ is an energy source in seeds
Starch for germination
_______ and ________ are structural carbohydrate components
Cellulose
hemicellulose
______ and ________ are a ready supply of energy
Monosaccharides
disaccharides
_________ are a short-term energy supply for muscles
Glycogen
_______ and ________ act as sweetening agents, coloring agents, and produce flavors
Monosaccharides
disaccharides
_______ act as thickening agents, gelling agents, emulsion stabilizers, water-holding agents and anticaking agents
Polysaccharides
Monosaccharides range from __ carbons to __ carbons
3
7
Monosaccharides have either a ______ or an _____ functional group in their linear form
ketone
aldehyde
The carbon chain of a monosaccharide is numbered from the aldehyde (C-__) or the ketone (C-__) functional group down.
1
2
__________ exhibit optical isomerism (D- and L-isomers)
Monosaccharides
The smallest monosaccharide is _________, which has ___ carbons
glyceraldehyde
3
Glyceraldehyde has ____ asymmetric carbon(s)
1
_______ is used as a reference compound to determine D-L isomerism
Glyceraldehyde
In the Fischer projections, OH group on the asymmetric carbon is on the _____ in the D-isomer and on the ____ in the L-isomer.
right
left
Apart from glyceraldehyde, D or L isomerism for other sugars refers ONLY to the n-___ carbon (___ from the bottom) and not any of the other asymmetric carbons that may be in the chain.
1
2nd
Optical isomers involving asymmetric carbons other than the carbon at the n-1 position are considered different sugars or _______.
epimers
All C6 aldehyde monosaccharaides are ______ of glucose.
epimers
Monosaccharides can be classified on the basis of ______ and __________
carbon number
functional group
The actual conformation of simple sugars is _____ in their crystalline state and in solution, but they are illustrated as ______ for simplicity
cyclic
linear
Cyclization is due to the formation of internal _______ and _______
hemiacetals
hemiketals
A hemiacetal is formed from an ______ and an _______
alcohol
aldehyde
A hemiketal is formed from a ______ and an _______
ketone
alcohol
In the cyclization of monosaccharides, these reactions are (intermolecular/intramolecular)
intramolecular
Hemiacetal formation in glucose (an aldohexose) forms a ________ ring
pyranose
Hemiketal formation in fructose (a ketohexose) forms a ________ ring
furanose
Glucose is an ________
aldohexose
Fructose is a _________
ketohexose
Cyclization results in an additional ________________ at the ___ position
asymmetric carbon
C1
The additional asymmetric carbon at the C1 position from cyclization is termed _________ carbon, and leads to ___ optical isomers, termed ________
anomeric
2
anomers
The cyclic form in which the OH group at the anomeric carbon is on the same side of the ring as C6 is termed ___
B
The cyclic form in which the OH group at the anomeric carbon is on the opposite side of the ring is termed ___
alpha
The crystalline form of the simple sugars is always _____.
cyclical
In solution, there is a dynamic equilibrium between the three
forms: ______, _____, and _______
alpha
beta
open chain
The dynamic equilibrium between a, B, and open-chain simple sugars is observed by following the ________ of _______ by a solution of the sugar
optical rotation
plane-polarized light
When pure ___-D-glucopyranose is dissolved in water, the optical rotation starts at 112o and gradually changes to 53o.
alpha
When pure ___-D-glucopyranose is dissolved in water, the optical rotation starts at 19o and gradually changes to 53o.
beta
______ is the phenomenon that causes the change in optical rotation
mutarotation
_______ is the result of the cyclic form opening up and re- cyclizing, coming to equilibrium with its _____.
Mutarotation
anomer
For _____, the equilibrium is roughly 62% α-D-glucopyranose and 37% β-D-glucopyranose, with only 1% in the open-chain form with the active ______ group.
glucose
aldehyde
The equilibrium of (glucose/fructose) is more complex than (glucose/fructose) since it is a ______
fructose
glucose
hemiketal
Cyclization via the formation of a _______ can produce either a five-membered ____ ring or a six-membered _____ ring
hemiketal
furanose
pyranose
The formation of furanose (five-membered) ring by attack of OH group at C-__ on C-__ keto group.
5
2
Formation of pyranose (six-membered) ring by attack of OH group at C-__ on C-__ keto group.
6
2
The aldehyde group present on ALDOSES has strong _________
reducing power
________ are capable of reducing metal ions (in an oxidation- reduction reaction that converts the _____ to a _________).
Aldehydes
aldehyde
carboxylic acid
As a group, ________ are generally termed “reducing sugars” and can be tested for and quantified by specific __________ reactions
monosaccharides
oxidation/reduction
The most common test for reducing sugars is _________, which involves the reduction of Cu(__) in the form of __________ to Cu(__) oxide.
Fehling’s test
II
copper tartrate
I
Fehling’s reagent only reacts with free ________ groups in the ________ form
aldehyde groups
open-chain
Only 1% of sugar is in the _____ form
open-chain
When
the ________ form is depleted, it is replenished by the opening of the ring forms (with which it is in equilibrium).
open-chain
Is fructose a reducing sugar? Does it have an aldehyde group?
- It is a reducing sugar
- It does not have an aldehyde group
Fructose is a reducing sugar since in a ____ medium, _________ takes place and fructose is converted to ______, which then is capable of reacting with the Fehling’s solution
basic
enolization
glucose
The reducing power of a sugar is lost when the ____ at the ______ carbon of the cyclic form is covalently bonded to another group because this prevents the ring from opening
OH
anomeric
Conversion to the open-chain form requires that an __ group bound to the ____ carbon reverts back to an _____ group
OH
anomeric
aldehyde
Is maltose a reducing sugar? What about sucrose?
Maltose: reducing
Sucrose: non-reducing
Maltose is composed of ______ and ______ linked by a ______ linkage
glucose
glucose
a-1-4
The anomeric carbon of the __nd glucose of _____ is not involved in the glycosidic bond, ring opening can occur at one end of the molecule, rendering it a reducing sugar
2
maltose
_____ is a reducing sugar but has half the reducing power of glucose because _______________________________
Maltose
one of the two anomeric carbons is used in the glycosidic bond
Sucrose is composed of _______ and ______ linked by a ____ glycosidic linkage
glucose
fructose
a-1-2
______ is a non-reducing disaccharide because both ______ carbons are tied up in the glycosidic bond, so the ring opening cannot occur
Sucrose
anomeric
______ reactions of sugars are the basis for _______ and the Maillard reaction
Dehydration
caramelization
Dehydration reactions can take place at temperatures below ____oC, and in ____ solutions, but they occur very slowly
100
dilute
Dehydration reactions are prevalent in concentrated sugar solutions at temperatures above 130oC, or in _____ pH
acidic
As water evaporates from the solution, ______ dehydration and oxidative _____ can take place, leading to the breakdown of the carbon chain into smaller units, which produce ____ compounds
molecular (internal)
fission
flavor
What are the two ways that water can be eliminated from a sugar molecule? Which one is predominant?
1) The loss of water from two sugar molecules by reaction of their hydroxyl groups
2) Elimination of water from within a sugar molecule, leading to the formation of highly unsaturated ring structures (predominant)
What does the loss of water from two sugar molecules by reaction of their hydroxyl groups lead to?
Random polymerization
What does the elimination of water from within a sugar molecule lead to?
The formation of highly unsaturated ring structures
A common intermediate formed during caramelization reactions by dehydration is _____________________
hydroxymethylfurfural (HMF)
Hydroxymethylfurfural (HMF) is formed from the loss of __ water molecules
3
HMF is formed from _______, which is converted to ______, and HMF once it loses 3 water molecules
fructopyranose
fructofuranose
Fragmentation reactions of highly unsaturated ring structures produce various (high/low)-molecular-weight, (saturated/unsaturated) and reactive compounds, which can ________
low
unsaturated
polymerize
Fragmentation of highly unsaturated ring structures produces _____, _____, and _____ under (acidic/alkaline) conditions
acetol
acetoin
diacetyl
alkaline
Extensive dehydration reactions eventually lead to the formation of an amorphous, charged brown pigment commonly called _______.
caramel
What are the two categories of browning reactions?
1) Oxidative (enzymatic)
2) Non-oxidative (non-enzymatic)
Oxidative browning is associated with browning of _______, and not related to carbohydrates
plant tissues
Oxidative browning is instigated by ___________, which oxidizes _______ into ________
polyphenol oxidase (PPO) mono- or dihydroxy phenols quinones
________ are quite reactive and can react non-enzymatically to polymerize into a brown pigment.
Quinones
Other enzymes are indirectly associated with browning, including oxidative enzymes such as ________ and _______, which can produce reactive ______ compounds that can undergo non-enzymatic browning
ascorbic acid oxidase
lipoxygenase
carbonyl
_________ reaction occurs when any concentrated sugar solution is heated.
Caramelization
Caramelization is used to produce _______ and _______
caramel syrup
caramel color
Caramel flavors are generally made from ___________
concentrated sucrose solutions
Caramel color are generally made from ________
glucose syrup
The two main reactions in caramelization are _______ and ________, producing (high/low) molecular weight (fat/water) soluble polymers that are very dark in color
dehydration
polymerization
high
water
__________ produces compounds that have a high tinctorial power
Caramelization
The Maillard reaction involves the reaction of ______ sugars with primary _______, generally amino acids and protein
reducing
amines
In the _____ reactions, color, flavor, and volatinle compounds are produced
Maillard
The _______ reaction is at the root of coffee aroma, popcorn aroma, roasted peanut flavor, and baked bread aroma
Maillard
In the Maillard reaction, the first reaction is the _________ of a primary amine and a reducing sugar to form a _______ followed by the formation of an __________
condensation
Schiff base
Amadori compound
The ______ compound in the Maillard reaction is comparable to HMF in caramelization
Amadori compound
What is the key intermediate in the Maillard reaction?
Amadori compound
The overall process of converting from the initial Schiff base to
an Amadori compound is termed _________________
Amadori rearrangement
The Amadori compound can lose _____ from within the molecule
water
Following the formation of the Amadori compound in the Maillard reaction, what are the major reactions at higher temperatures?
Dehydration and fragmentation
What is the difference between the Maillard reaction at high temperatures and caramelization?
An amine group attached to the sugar in the Maillard reaction and hence the end products tend to contain nitrogen in their structure.
In the Maillard reaction, fragmentation produces short-chain highly unsaturated ______ and _____ compounds that can polymerize and/or be released as ______ into the environment
carbonyl
amino
volatile
The net result of the Maillard reaction is that ____ pigments and volatile compounds containing ______ are formed.
brown
nitrogen
___________ is a subcomponent of the Maillard reaction.
Strecker degradation
The Strecker degradation involves the reaction of free ___________ with the ____________ intermediates produced by either the Maillard reaction or caramelization reactions
amino acids
dicarbonyl
The products formed from the Strecker degradation are ____, ______, ______, and _______, which are compounds that contribute to the characteristic aroma of roasted foods
CO2
ammonia
formaldehyde
pyrazines
The Strecker aldehyde and _______ give rise to strong _____
aminoketone
odors
Ethanal, methylpropanal, and 2-phenylethanal are common _________
Strecker aldehydes
_______ is a Strecker aldehyde with a fruity, sweet aroma
Etanal
_________ is a Strecker aldehyde with a malty aroma
Methylpropanal
_________ is a Strecker aldehyde with a flowery/honey like aroma
2-phenylethanal
Condensation of two __________ may yield pyrazine derivatives that are also powerful aroma compounds
aminoketones
______________ reactions are used commercially to produce artificial flavor compounds
Strecker degradation
By reacting _____ and selected ________ or mixtures thereof under the proper conditions, one can produce a wide variety of flavors such as chocolate, bread, caramel, almond, and many other flavors.
sugars
amino acids
Can sweetness be measured?
No, it is a subjective response
______ is considered the least sweet sugar, while _______ is considered the most sweet
Lactose
fructose
_________ is sucrose that is hydrolyzed to a mixture of glucose and fructose
Invert sugar
Is invert sugar sweeter than sucrose?
No: invert (65) and sucrose (100)
Sweetness (increases/decreases) with increasing temperature
decreases
What attributes the decrease in sweetness with increasing temperature?
The change in the relative concentrations of the open-
chain, α, and β forms, which differ in sweetness.
Is sweetness perceived the same way by different people?
No
The relative sweetness of sugar is changed in the presence of other components such as ____, ____, other ____, and a host of other components.
salts
acids
sugars
Alcohol (increases/decreases) sweetness
increases
Sugars are (sweeter/less sweet) when mixed together than when tasted separately, thus giving a ______ effect
sweeter
synergistic
What is the only way to determine suitability for sugars?
Run taste panels and evaluate the overall response
Sweetening power is related to sugar ______
solubility
_______ has the highest saturation point (85%), while ______ has the lowest (20%)
Fructose
lactose
________ is a very important criterion when high sugar concentrations are required to inhibit microbial growth
Solubility
If the solubility of the sugar is too low, it can _______, making the product texture ______.
crystallize
grainy
Limitations in _______ may be encountered in sweetened condensed or evaporated milk and ice cream
solubility
since lactose has low solubility
A common method used to avoid sugar crystallization is to __________________, which inhibits their crystallization.
mix two sugars together
Sugars effectively bind _____, making it unavailable for microorganisms due to the lowering of the ________ of the system, acting as a preservative
water
water activity
If browning is not desired, it can be minimized by using _______
sucrose
_________ prevent the ______ of meat pigments
Reducing sugars
oxidation
_______ act as humectants, flavor binding agents, and viscosity enhancers
Humectants
Sugars alcohols are produced by reducing the ______ group to a ______ group by _______
aldehyde
hydroxyl
hydrogenation
Sugar alcohols are only absorbed by ___________, thereby contributing fewer calories than sugars.
passive diffusion
__________ are poorly metabolized by the microbial flora of the mouth – do not contribute to dental caries
Sugar alcohols
Dental caries are caused by ____ produced by the microflora from the ________ of sugars
acids
fermentation
Most sugar alcohols are (more/less) sweet than sugars
less
The most common sugar alcohols are _____ and ______
glucitol
mannitol
______ is a sugar alcohol which has comparable sweetness to sucrose
Xylitol
Xylitol is produced from _____, a polymer of ______
xylan
xylose
Xylan is _____ to xylose and _______ using a nickel catalyst to produce xylitol
hydrolyzed
hydrogenated
Xylitol can be produced from xylose by ______ fermentation, or from glucose by _________
yeast
enzymatic conversion
________ are used as bulking agents and viscosity enhancers in artificially sweetened products to provide “body“.
Sugar alcohols
________ are used as water-binding agents to plasticize intermediate-moisture foods and reduce the water activity of the food system without adding excessive sweetness
Sugar alcohols
