Carbohydrates II Flashcards
What are the three common polysaccharides?
- Starch
- Cellulose
- Pectin
Guar gum and locust bean gum are _____ gums
seed
Gum arabic and gum tragacanth are _________ gums
plant exudate
Agar and carrageenan are _______ gums
seaweed
Dextran and xanthan gum are _______ gums
microbial
Other than cellulose, the most abundant form of stored carbohydrate is ______
starch
______ is the main source of dietary carbohydrate
Starch
_____ is used extensively in the food industry due to its unique properties as a thickening/texture-modifying agent and as a source of sugars and dextrin
Starch
Starch is a source of _____ and _____
sugars
dextrins
Starch is made up exclusively of _______
D-glucose
The two fractions of starch are ______ and ______
amylose
amylopectin
________ is a long-chain linear polymer composed of D-glucose linked by _____ glycosidic bonds
Amylose
a-1-4
_______ is a branched polymer, composed of D-glycose linked by _____ glycosidic bonds in the linear position, and _____ bonds at its branch points
Amylopectin
a-1-4
a-1-6
Starch is found in most plant sources as hard, water-(soluble/insoluble) ______
insoluble
granules
______ contains almost 100% amylopectin
Waxy maize
________ contains 28% amylose and 62% amylopectin
Regular corn starch
Starch is readily isolated from the plant source by ______, then centrifuged out of solution and dried
wet milling
Isolated starch produces a _________ composed of discrete starch granules
dry white powder
Each starch granule is made up of ______ amylose and amylopectin tightly bound and held together by _____ bonding between the polymers
anhydrous
hydrogen
Heating in the presence of moisture breaks the ________ bonds,
leading to ________.
hydrogen
gelatinization
Swelling of the granule is due to the adsorption of ______, which is facilitated by _____
water
heat
The swelling of starch granules increases ________, and breaks________
kinetic energy
hydrogen bonds
During gelatinization, starch granules are ______ as ____ molecules access the __ groups on the polymer
hydrated
water
OH
Gelatinization temperature is a function of the _______
starch source
_________ occurs between 60-70oC
Loss of granular integrity (gelatinization)
When the granules have swollen extensively, the viscosity of the solution (increases/decreases) drastically, which is called ________
increases
pasting
If the swollen granule solution is stirred, the granules will break up and disperse to form __________
a colloidal solution
If the concentration of starch is high during gelatinization, it will form a ____ upon _____
gel
cooling
If the concentration of starch is high during gelatinization, it will form a ____, and not a _____
viscous solution
gel
What are the factors that influence the gelatinization of starch?
- Concentration
- Amylose/amylopectin
- Average molecular weight of the starch
- Rate of cooling
- Presence of other components
________ is a linear polymer that tends to form a long thin helical filament-like structure in solution.
Amylose
______ has very low solubility as it readily hydrogen bonds to neighboring polymers to form large aggregates that precipitate out of solution.
Amylose
On its own, _______ is useless functionally in food systems as it is effectively insoluble.
amylose
________ is a highly branched water-dispersible macromolecule.
Amylopectin
_________
forms a viscous solution; branching produces a tangled net-like web in solution.
Amylopectin
In the presence of ________, which acts like a cross-linking agent, a three- dimensional gel can form, entrapping ______.
amylose
water
A gel forms when the kinetic energy of the system is (increased/reduced) sufficiently to allow random _________ to re-form
reduced
hydrogen bonds
The extensively hydrogen bonded starch molecules trap ______ within the matrix formed, producing a _____.
water
gel
Starch gels become _______ with time - a generally undesirable aspect of starch behavior in food systems
firmer
What is the cause of retrogradation?
Continued hydrogen bond formation between starch molecules
What are the two problems caused by retrogradation?
1) Texture changes
2) Syneresis
What is syneresis?
When a gel tightens up so much that it starts to exude water
________ commonly causes starch gels to become more opaque with time.
Retrogradation
___________ is one of the key processes responsible for the staling of bread and stiffening of pie fillings.
Retrogradation
Normal ____ starch (about 28% amylose) will set to a rigid (transparent/opaque) gel.
corn
opaque
Starch from ________, which is a genetically modified low- amylose corn (almost devoid of amylose), will not form a gel at all.
waxy maize
_______ does not contain amylose
waxy maize
______ starch (~23% amylose) and ______ starch (~28% amylose) form reasonably stable gels that tend to maintain their clarity and do not stiffen appreciably with time
Potato
tapioca
The stability of potato and tapioca starch is due to the high ___________ of the starches, making them less mobile, which decreases the rate of hydrogen bond formation
molecular weight
______ tend to retard gel formation and retrogradation
Sugars
__________________ tend to inhibit retrogradation and gelation by forming complexes with starch
Surface-active agents (surfactants)
Surfactants are most noticeable with ___________ starch systems
high-amylose
_______ compete for available water and interfere with starch- to -starch hydrogen bonding.
Sugars
The pH of most foods lies in the range of ______.
4-7
In highly ______ foods, particularly when heated or stored for extensive periods, there is the possibility of a reduction of the _______ due to the _______ of starch
acidic
viscosity
hydrolysis
_________ processing can affect the final viscosity of starch
Thermal
Why does ionic strength have minor effects in starches?
Since starches have no ionizable groups
Which two factors have minor effects on starches?
- pH
- Ionic strength
______ are capable of dramatically changing how a starch behaves in terms of gelation and viscosity.
Proteins
The interaction with starch and _______ produces a smooth gel known as _______
milk proteins
pudding
In North America, most of our starch is derived from ______
corn
In pre-gelatinized starches, granules are ____________________, which causes them to swell, and are then _______
heated below the gelatinization temperature of the starch
drum-dried
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
_________ starches are convenient for food processors and are used extensively in the food industry .
Pre-gelatinized
_________ are commonly termed thin-boiling starches.
Acid-modified starches
Acid-modified starches are produced by holding starch just below its gelatinization temperature in an ______ medium, then it is ______ and ____
acidic
neutralized
dried
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
__________ produce easy-to-handle low-viscosity fluids that can be poured into molds and will set into a firm gel upon cooling
Acid-modified starches
Maximum viscosity is normally reached when the granules are ________ extensively but still intact
swollen
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 are used as cross-linking agents
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
What is the overall objective of starch derivatives?
To reduce polymer-polymer hydrogen bonding via steric hindrance or the introduction of charged groups
What are starch derivatives used to?
- Control retrogradation and staling
- Improve freeze/thaw stability
- Reduce textural and opacity changes
Starch derivatives are formed by introducing _________ or ________ into the granules
hydroxypropyl
acetyl
In starch derivatives, _________ prevents the polymers from associating as readily as in natural starch
steric hindrance
________ can be added to produce starch derivatives, which increase stability against retrogradation because of their _______
Orthophosphate charge (like charges repel)
What other types of new groups can be introduced in a starch?
- Ester
- Ether
- Acetyl
Give an example of a specialty derivative?
Introduction of hydrophobic side chains enables starches to be used as emulsifiers and emulsion stabilizers
_____ is used to oxidize a portion of the _______ groups to _______ groups in starches
Sodium hypochlorite (NaOCl)
hydroxyl
carboxyl
Which groups may be introduced in oxidized starches?
Aldehyde and ketone groups
The solubility of oxidized starches is _____ dependent
pH
What is the advantage and the disadvantages of oxidized starch?
Advantage: stabilized against retrogradation
Disadvantage: more susceptible to variations in pH and ionic strength in a food product
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
Acid hydrolysis may be used for the production of _______ or as a preliminary step in the production of ______ from ______
dextrins
sugars
starch
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
_________ from pyroconversion can be controlled to produce desired ranges of viscosity
White dextrins
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
The color of yellow dextrins is due to the ______________ reaction
non-enzymatic browning (caramelization)
In pyroconversion, the viscosity and degree of polymerization of __________ can be controlled
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
Over half of the isolated starch produced is converted to ______ and ______.
syrups
sugars
___________ is commonly a preliminary step in the conversion of starch to syrups and sugars.
Acid hydrolysis
In acid hydrolysis, starch is ________ and hydrolyzed in the presence of ______ and pressurized steam
gelatinized
HCl
Acid hydrolysis is extensive and random, producing ______ and ______
dextrins
sugars
By controlling acid hydrolysis, the degree of ____________ can be manipulated to a degree to produce glucose syrups of various viscosities and sweetness.
dextrinization
Starch breakdown can be followed by measuring the ___________ content of the hydrolysate.
reducing sugar
Reducing sugar content (increases/decreases) with hydrolysis as mono-, di- and oligosaccharides are produced.
increases
Reducing sugar content is expressed in terms of ______________
dextrose equivalents (D.E)
If the hydrolysis of starch is 100% complete, then D.E. = ______
100
What is the equation for D.E?
Acid hydrolysis cannot yield dextrose equivalents much beyond ____ since an equilibrium is reached between ________ and ___________.
50
hydrolysis
repolymerization
__________ 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
The enzymes that are capable of hydrolyzing starch are commonly termed _________ - these enzymes are found in most living systems.
amylases
Commercially, the sources of _____________ are microorganisms because relatively large quantities of selective enzymes can be obtained through genetic manipulation and the enzymes are simple to isolate.
amylases
_________ is an endoenzyme - can attack anywhere within the starch
molecule other than the α-1,6 branch point.
a-amylase
_________ is also known as liquefying enzyme
a-amylase
__________ causes viscosity of a starch solution to drop rapidly
a-amylase
Random internal bond breakage (increases/reduces) the overall molecular weight of starch, which is done by _________
reduces
a-amylase
The end-products of the __________ enzyme are mainly oligosaccharides together with some glucose, maltose, and pannose
a-amylase
_________ is a trisaccharide containing the α- 1,6 branching linkage
Pannose
________ is an exoenzyme that attacks the non-reducing end of the starch
chain.
B-amylase
__________ produces _________ by hydrolyzing the a-1,4 bond every two glucose units over
B-amylase
maltose
_________ is commonly known as a saccharifying enzyme
B-amylase
__________ develops sweetness rapidly, but viscosity does not change significantly
B-amylase
__________ are capable of removing single glucose units from the non-reducing end of starch and to split ________ into two glucose units
Glucoamylases
maltose
Glucoamylases act from the __________ end of the starch, to split __________ into two glucose units
non-reducing end
maltose
Combined action of α- and β-amylase and glucoamylase leaves ‘limit _______” - largely the trisaccharide ________.
dextrins
pannose
___________ hydrolyzes a-1,6 glycosidic linkages
Pullulanase
_________ attacks the branch points so that the trisaccharide pannose can be broken down to _______ and ________
Pullulanase
glucose
maltose
a-amylase, B-amylase, glucoamylase, pullulanase brovide a means of converting starch to predominantly __________ (______), which produces syrups with a (high/low) D.E.
D-glucose
dextrose
high
At D.E. > 90, _________ can be crystallized out of solution and obtained in pure form in a manner very similar to sucrose refining.
glucose
________ is a useful sweetener, but not as sweet as sucrose.
Glucose
D-glucose is isomerized to D-
fructose using _____________.
glucose isomerase
________ has about 1.3 times the sweetening power of glucose
and is somewhat sweeter than sucrose.
D-Fructose
Glucose isomerase is capable of converting about ____% of D- glucose into D-fructose.
45
High-fructose corn syrups are similar to ________ and are in direct competition with ________.
invert sugars
sucrose
Sucrose is commonly inverted using the enzyme __________ to stabilize its sweetness in _________ environments
invertase
acidic
Why is sucrose inverted?
Glycosidic link in sucrose is acid labile, and readily hydrolyzed by heat or acid
For acidic beverages, sweetness can be stabilized by ________
inversion
The term ‘”inverted” refers to the change in the specific rotation of ________________ by a sucrose solution
plane-polarized light
In a fully converted solution, the direction of rotation is _________
inverted (from +66.5o to -39o)
Why does high-fructose corn syrup have great value?
1) Sweeter than glucose
2) More soluble
3) Does not crystallize readily
High-Fructose Corn Syrup becomes sweeter with (increasing/decreasing) temperature
decreasing
Why does HFCS not crystallize readily? What is this good for?
- Because it is a mixture of sugars
- Good for frozen products
____________ have made large inroads into the sucrose market and made the sweetener industry more competitive.
High-fructose corn syrups
