Carbohydrates - Summary Flashcards
_________ is a trisaccharide formed of galactose, glucose, and fructose
Raffinose
_________ is a tetrasaccharide, formed of glucose, fructose, and two galactose
Stachyose
Monosaccharides range from __ carbons to __ carbons
3
7
The carbon chain of a monosaccharide is numbered from the aldehyde (C-__) or the ketone (C-__) functional group down.
1
2
The smallest monosaccharide is _________, which has ___ carbons
glyceraldehyde
3
Optical isomers involving asymmetric carbons other than the carbon at the n-1 position are considered different sugars or _______.
epimers
Hemiacetal formation in glucose (an aldohexose) forms a ________ ring
pyranose
Hemiketal formation in fructose (a ketohexose) forms a ________ ring
furanose
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
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
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
________ are capable of reducing metal ions (in an oxidation- reduction reaction that converts the _____ to a _________).
Aldehydes
aldehyde
carboxylic acid
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
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
Maltose is composed of ______ and ______ linked by a ______ linkage
glucose
glucose
a-1-4
_____ 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
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
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
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
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
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
___________ 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
Methylpropanol
_________ 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
______ is considered the least sweet sugar, while _______ is considered the most sweet
Lactose
fructose
Sweetness (increases/decreases) with increasing temperature
decreases
Alcohol (increases/decreases) sweetness
increases
Sweetening power is related to sugar ______
solubility
_______ has the highest saturation point (85%), while ______ has the lowest (20%)
Fructose
lactose
If browning is not desired, it can be minimized by using _______
sucrose
_________ prevent the ______ of meat pigments
Reducing sugars
oxidation
Sugars alcohols are produced by reducing the ______ group to a ______ group by _______
aldehyde
hydroxyl
hydrogenation
Most sugar alcohols are (more/less) sweet than sugars
less
______ is a sugar alcohol which has comparable sweetness to sucrose
Xylitol
Starch is made up exclusively of _______
D-glucose
When the granules have swollen extensively, the viscosity of the solution (increases/decreases) drastically, which is called ________
increases
pasting
If the concentration of starch is high during gelatinization, it will form a ____, and not a _____
viscous solution
gel
______ has very low solubility as it readily hydrogen bonds to neighbouring polymers to form large aggregates that precipitate out of solution.
Amylose
__________ forms a viscous solution; branching produces a tangled net-like web in solution.
Amylopectin
Starch gels become _______ with time - a generally undesirable aspect of starch behavior in food systems
firmer
________ commonly causes starch gels to become more opaque with time.
Retrogradation
Starch from ________, which is a genetically modified low- amylose corn (almost devoid of amylose), will not form a gel at all.
waxy maize
______ tend to retard gel formation and retrogradation
Sugars
__________________ tend to inhibit retrogradation and gelation by forming complexes with starch
Surfactants
Surfactants are most noticeable with ___________ starch systems
high-amylose
Pre-gelatinized starches are dispersible in _________ and requires less ___ or ____ to develop viscosity
cold water
heat
time
A higher amount of ___________ starch is required to attain similar viscosity effects as with an untreated starch.
pre-gelatinized
_________ are commonly termed thin-boiling starches.
Acid-modified starches
Why is acid used in acid-modified starch?
To partially and randomly hydrolyze the glycosidic linkages in the starch granule without breaking up the INTEGRITY of the granule
Acid-modified starches are used in _________ manufacture
candy
Swollen granules normally break down, but _________ starches are held together chemically so that the swollen granule retains its integrity
cross-linked
What compounds are used as cross-linking agents?
- Acetic anhydride
- Citric anhydride
- Adipic anhydride
________ compounds can bridge two _______ groups from adjoining polymers, and hold the swollen granule structure together
Anydride
hydroxyl
The granules swell (more/less) in cross-linked starch
less
The maximum viscosity is (higher/lower) in cross-linked starch
lower
_________ are less susceptible to acid hydrolysis
Cross-linked starches
Starch derivatives are formed by introducing _________ or ________ into the granules
hydroxypropyl
acetyl
________ can be added to produce starch derivatives, which increase stability against retrogradation because of their _______
Orthophosphate charge (like charges repel)
_____ is used to oxidize a portion of the _______ groups to _______ groups in starches
Sodium hypochlorite (NaOCl)
hydroxyl
carboxyl
The solubility of oxidized starches is _____ dependent
pH
What are the two basic types of starch conversions?
1) Dry pyroconversion
2) Acid hydrolysis
_________ is used for the production of cold-water-soluble starches
Dry pyroconversion
___________ is used for wet conversion
Acid hydrolysis
In pyroconversion, starch granules are sprayed with dilute ______ and subjected to relatively (high/low) temperatures
HCl
high
Which four reactions may take place in pyroconversion?
1) Hydrolysis of a-1-4 and a-1-6 linkages
2) Transglucosidation
3) Repolymerization (free sugars undergo caramelization)
4) Caramelization (free sugars undergo caramelization)
__________ is the breaking of 1,4-linkages and the formation of other linkages, generally random in nature (1,3 or 1,5)
Transglucosidation
What are the three products formed by pyroconversion?
1) White dextrins
2) Yellow dextrins
3) British gums
_________ dextrins are soluble in cold water
White
In pyroconversion, under conditions of high moisture, high acid, and relatively low temperature, hydrolysis predominates, and _________ are formed
white dextrins
In pyroconversion, under low moisture, moderate acid, and higher temperatures, _______ are formed
yellow dextrins
In pyroconversion, _______________ are produced under conditions with little or no acid used, and higher temperatures
British gums
The pyroconversion products ___________ are dark in color with little hydrolysis and much ore transglucosidation
British gums
The pyroconversion product _________ is much more viscous and capable of forming a stiff gel; used extensively in candy manufacture
British gums
Starch breakdown can be followed by measuring the ___________ content of the hydrolysate.
reducing sugar
Reducing sugar content is expressed in terms of ______________
dextrose equivalents (D.E)
What is the equation for D.E?
__________ is not the best means of producing very sweet, high D.E syrups
Acid hydrolysis
To obtain syrups that have high D.E., ____________ of gelatinized starch is carried out.
enzymatic conversion
_________ is also known as liquefying enzyme
a-amylase
_________ is a trisaccharide containing the α- 1,6 branching linkage
Pannose
_________ is commonly known as a saccharifying enzyme
B-amylase
__________ develops sweetness rapidly, but viscosity does not change significantly
B-amylase
_________ attacks the branch points so that the trisaccharide pannose can be broken down to _______ and ________
Pullulanase
glucose
maltose
Why is sucrose inverted?
Glycosidic link in sucrose is acid labile, and readily hydrolyzed by heat or acid
By controlled hydrolysis, the more amorphous regions of cellulose can be hydrolyzed, leaving behind _______________
microcrystalline cellulose
What is CMC?
Carboxymethyl cellulose
CMC is formed by hydrating cellulose in a strongly (acidic/basic) solution, and then reacting it with ___________
basic
sodium chloroacetate
_______ is a more soluble cellulose polymer that is capable of contributing to the _______ of a solution as well as forming ________
CMC
viscosity
weak gels
The presence of ________ groups means that CMC is susceptible to _____ changes
carboxyl
pH
The presence of ionized carboxyl groups in CMC allows _____ ions to be used to cross-link the polymers to form a _____
divalent
gels
_____________ and _____________ cellulose derivatives are quite soluble and their viscosities are not affected by pH or salts since these derivatives are __________
hydroxypropyl cellulose
methyl cellulose
non-ionic
Hydroxypropyl cellulose and methyl cellulose are formed in (acidic/basic) solutions
basic
A pectic substance is a complex carbohydrate largely made up of ______________, which can be extracted from plant material
polygalacturonic acid
What are the three categories of pectic substances?
1) Pectic acids
2) Pectinic acids
3) Pectin
_________ are polymers of predominantly polygalacturonic acid free of methyl ester groups.
Pectic acids
_________ are polymers of polygalacturonic acid with some degree of methylation (low methoxy pectin).
Pectinic acids
__________ are polymers of polygalacturonic acid with >50% of the carboxyl groups methylated.
Pectin
The categories of pectic substances are based on their degree of the ________ of the ________ groups
methylation
carboxyl
Most pectin is obtained as a by-product of the ______ industry, form which pectin is extracted using dilute ______
citrus
acid
Pectin with a DM of 50 serves well for jellies (with/without) suspended material, while for jams (with/without) particles, a DM > 75 is required
without
with
Rapid setting pectin has a (higher/lower) DM
higher
High-DM pectin requires special extraction procedures and will set at (higher/lower) temperatures
higher
_________ pectins, such as _____ and ______, are useful in the manufacture of diet jams and jellies
Low-methoxy
pectic
pectinic acids
Low-methoxy pectins are produced by controlled hydrolysis of the ______ groups using (acid/alkaline) conditions
methyl
alkaline
______ and _________ are capable of producing a gel with divalent ions to cross-link the polymers at the carboxyl groups
CMC
low-methoxy pectins
The pH range for gel formation is much broader in ________ pectins
low-methoxy
Guar gum and locust bean gums are both ____________
galactomannans
Galactomannans consist of a ______ backbone (_____ linkages) with ______ side groups (______ linkages)
mannose
B-1,4
galactose
a-1,6
The most important property of guar gum is its ability to hydrate very rapidly in ________ and form a very _______ solution.
cold water
viscous
In _______ there is a D-galactose branch on the mannose backbone every other mannose unit
guar gum
In ________ there is a D-galactose branch on the mannose backbone every fourth or fifth mannose unit
locust bean gum
________ gum requires more heating to go into solution than _______ gum
Locust bean
guar
________ are all charged heteropolysaccharides
Plant exudate gums
________ is a polysaccharide consisting of D-galactose, L-arabinose, L-rhamnose and D-glucuronic acid
Gum arabic
A number of _____ are said to be present in the side chain portions of _________
sugars
plant exudate gums
Plant exudate gums are charged due to the presence of ________
glucoronic acid
The distinguishing feature of gum arabic is that it is _____________
extremely soluble in water
________ is commonly used to convert citrus essential oil flavor emulsions to a water-dispersible powder by spray drying.
Gum arabic
Giant kelp (brown algae) is a source of _________
alginates
_________ is a polysaccharide composed of D- and L-galactose and 3,6- anhydro-D-galactose units
Carrageenan
Some of the galactose moieties in _______ are sulfonated
carrageenan
________, like starch, is made up of two fractions (linear and branched)
Carrageenan
__________ has the UNIQUE ability to complex with milk proteins to form a very light gel
Carrageenan
_______ are made up of largely linear polymers of D-mannuronic and L-glucuronic acids.
Alginates
Presence of ______ groups makes _______ sensitive to pH and ionic strength of a food system.
carboxyl
alginates
_______ is extracted in the form of their sodium salts, so that they will be readily soluble.
Alginates
Similarly to the behavior of carboxymethyl cellulose and low-methoxy pectin, ________ gels can be produced by cross-linking using divalent ions such as ______.
alginates
calcium
Many microorganisms produce “______” which are extracellular polysaccharides.
slimes
How do dextrans differ from starch?
Glucose units are linked by a-1,6 rather than a-1,4
Where are the branch points of dextrans?
a-1,3
____________ is the most common organism used to produce dextran by fermentation of _______.
Leuconostoc mesenteroides
sucrose
Xanthan gum is made up of D-______, D-______, and D-___________, present in approximately a _____ ratio
glucose
mannose
galacturonic acid
3:3:2
What is the viscosity of xanthan gum affected by? What happens when it is removed?
- Affected by shear
- Viscosity returns after shear is removed (pseudoplastic)
_______ gum is very useful in highly acidic foods
Xanthan
________ will form a gel with locust bean gum in very low concentrations
Xanthan gum
_______ is very useful in production of instant puddings or gels without the need for heat.
Xanthan gum
