Carbohydrates III Flashcards
_________ is a polymer of D-glucose units linked by a B-1,4 glycosidic linkage
Cellulose
Human body lacks enzymes capable of hydrolyzing the _____
glycosidic linkage, making _______ indigestible.
B-1,4
cellulose
_______ exists only in a linear form with no branched counterpart.
Cellulose
________ is present as fiber-like bundles which have extensive amounts of crystalline regions - highly organized by _______.
Cellulose
hydrogen
Cellulose is often accompanied by other carbohydrates, ______, ________ and ______ to form the structural components of most plant tissues
hemicelluloses
pectic substances
lignin
Durability of ________ is well-known
cellulose
Do enzymes that are capable of hydrolyzing cellulose exist in nature?
Yes, but no one has successfully applied them commercially for the production of glucose
__________ of cellulose is quite difficult to perform
Acid hydrolysis
________ is non-nutritive in nature, and can be used for low-calorie products
Cellulose
By controlled hydrolysis, the more amorphous regions of cellulose can be hydrolyzed, leaving behind _______________
microcrystalline cellulose
Microcrystalline cellulose can be used as a __________ without contributing calories
bulking agent
Microcrystalline cellulose can be used as a ________ and ________
bulking agent
plating agent
What is a plating agent used for?
To convert liquid products into free-flowing powders by adsorption
What is CMC?
Carboxymethyl cellulose
________ is a methylated derivated of pure cellulose
Carboxymethyl cellulose
CMC is formed by hydrating cellulose in a strongly (acidic/basic) solution, and then reacting it with ___________
basic
sodium chloroacetate
What is the net result of the CMC reaction?
Addition of a carboxymethyl group onto the chain
_______ 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 properties of CMC can be modified at will based on the __________ and the degree of __________
molecular weight of the polymer
derivatization
The presence of ________ groups means that CMC is susceptible to _____ changes
carboxyl
pH
______ may precipitate out of solution at its isoelectric point
CMC
If the pH is above the pKa of the carboxyl groups, the CMC polymers (attract/repel) each other
repel
The presence of ionized carboxyl groups in CMC allows _____ ions to be used to cross-link the polymers to form a _____
divalent
gel
______ has found wide application in the food industry as a viscosity- enhancing agent that does not contribute any calories.
CMC
______ is used in ice cream where it provides a smooth texture and inhibits ice crystal growth during storage.
CMC
_____________ 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
______ substances are polysaccharides associated with the _________ between plant cell walls
Pectic
middle lammella
__________ act as a binder to hold the cells together
Pectic substances
A pectic substance is a complex carbohydrate largely made up of ______________, which can be extracted from plant material
polygalacturonic acid
The basic unit of pectic substances is __________
galacturonic acid
The carboxyl groups of galacturonic acid may be ________ with _______ groups or may be present as a free acid or its _______
esterified
methyl
salt
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
The major use of ________ is for the production of jams and jellies, which use sugar to prevent microbial growth by reducing __________.
pectin
water activity
What must be present for pectin to form a suitable gel? What is the pH range?
- Sugar, acid, water
- 2.8-3.2
In a pH range of 2.8 to 3.2, the _______ charge of the residual carboxyl groups in pectin is _______, while the sugar competes for water of hydration, which allows the polymers to form a gel
repulsive
reduced
Can pectin form a gel without sugar?
Yes, but large amounts of pectin are required (sugar is needed to lower water activity)
Most pectin is obtained as a by-product of the ______ industry, form which pectin is extracted using dilute ______
citrus
acid
What determines the quality and price of pectic substances?
Degree of methylation
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
________ pectin is useful in preventing particulate material from settling out
High-DM
_________ 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
The enzyme _________ may hydrolyze methyl groups to produce low-methoxy pectins
pectin methyl esterase
______ and _________ are capable of producing a gel with divalent ions to cross-link the polymers at the carboxyl groups
CMC
low-methoxy pectins
Are sugars required to form a gel in low-methoxy pectins? Why/Why not?
- No
- Owing to the cross-linking of the polymers
The pH range for gel formation is much broader in ________ pectins
low-methoxy
In low-methoxy pectins, for diet products to be shelf-stable, __________ are generally required to compensate for the osmotic effect (water activity reduction) that is lost when _____ is not used in the product.
antimicrobial agents
sugar
Seeds of some plants contain unique polysaccharides called _____.
gums
Two important seed gums are _______ and __________.
guar gum
locust bean gum
Guar gum and locust bean gums are both ____________
galactomannans
Galactomannans are polymers of _______ and ________
galactose
mannose
Galactomannans consist of a ______ backbone (_____ linkages) with ______ side groups (______ linkages)
mannose
B-1,4
galactose
a-1,6
______ is derived from a leguminous plant that is widely grown in India and Pakistan.
Guar gum
In _______, the ratio of mannose to galactose is roughly 2:1
guar gum
The most important property of guar gum is its ability to hydrate very rapidly in ________ and form a very _______ solution.
cold water
viscous
_______ is particularly useful in assisting in the rehydration of dry powders used in “instant products”
Guar gum
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
In ________, the ratio of mannose to galactose is in the range of 4:1 to 5:1
locust bean gum
________ gum requires more heating to go into solution than _______ gum
Locust bean
guar
________ is used extensively in ice cream to impart a smooth meltdown and freeze/thaw resistance; also used in the baking industry to produce softer doughs.
Locust bean gum
From a functional standpoint, _____ gum and _____ gum are largely interchangeable
guar
locust bean
How does the viscosity of gums change with pH?
It doesn’t
How is the stability of gums changed with processing?
Not very affective
Guar gum and locust bean gums are compatible with _____, ______, and other gums
starches
cellulose
________ and _______ are often used to subtly modify the texture of other gums
Guar gum
locust bean gum
________ are obtained by wounding specific tropical trees and shrubs and collecting the exudate.
Plant exudate gums
The main plant exudate gums are _____, _____, _____, and ______
arabic
ghatti
karaya
tragacanth
________ 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
The major use of _________is as a flavor carrier/dispersant.
gum arabic
________ is commonly used to convert citrus essential oil flavor emulsions to a water-dispersible powder by spray drying.
Gum arabic
_______ is also extensively used to inhibit sugar crystallization and as a thickener in candies, jellies and chewing gums.
Gum arabic
Irish moss is a source of ________
carrageenan
Red algae is a source of ______
agar
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
________ is used extensively to suspend insoluble chocolate solids in chocolate milk and also used in ice cream to minimize drip.
Carrageenan
_____ is similar to carrageenan in composition
Agar
_______ has the unique ability to form a thermoreversible gel that sets at about 40oC.
Agar
________ is best known for its use in bacteriological media
Agar
______ is used as a gelling agent for bakery products, confections, meat and fish products.
Agar
_______ 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
How do dextrans differ from starches?
Do not form organized crystalline granules
____________ is the most common organism used to produce dextran by fermentation of _______.
Leuconostoc mesenteroides
sucrose
The chain length and degree of branching of the polymer in _________ can be controlled genetically, therefore, choosing the right _______ allows a range of desired properties
dextrans
organism
Xanthan gum is a complex heteropolysaccharide produced by _____________
Xanthmonous campestris
Xanthan gum is made up of D-______, D-______, and D-___________, present in approximately a _____ ratio
glucose
mannose
galacturonic acid
3:3:2
Xanthmonous campestris can produce ________ from a variety of cheap carbohydrate substrates
xanthan gum
How does the viscosity of xanthan gum change with temperature?
It doesn’t - it has excellent heat stability
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)
What is the viscosity of xanthan gum independent of?
- Independent of pH
_______ 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
