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2) Food Chemistry I > Carbohydrates II > Flashcards

Carbohydrates II Flashcards

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1
Q

What are the three common polysaccharides?

A
  • Starch
  • Cellulose
  • Pectin
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2
Q

Guar gum and locust bean gum are _____ gums

A

seed

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3
Q

Gum arabic and gum tragacanth are _________ gums

A

plant exudate

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4
Q

Agar and carrageenan are _______ gums

A

seaweed

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5
Q

Dextran and xanthan gum are _______ gums

A

microbial

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6
Q

Other than cellulose, the most abundant form of stored carbohydrate is ______

A

starch

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7
Q

______ is the main source of dietary carbohydrate

A

Starch

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8
Q

_____ 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

A

Starch

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9
Q

Starch is a source of _____ and _____

A

sugars

dextrins

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10
Q

Starch is made up exclusively of _______

A

D-glucose

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11
Q

The two fractions of starch are ______ and ______

A

amylose

amylopectin

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12
Q

________ is a long-chain linear polymer composed of D-glucose linked by _____ glycosidic bonds

A

Amylose

a-1-4

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13
Q

_______ is a branched polymer, composed of D-glycose linked by _____ glycosidic bonds in the linear position, and _____ bonds at its branch points

A

Amylopectin
a-1-4
a-1-6

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14
Q

Starch is found in most plant sources as hard, water-(soluble/insoluble) ______

A

insoluble

granules

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15
Q

______ contains almost 100% amylopectin

A

Waxy maize

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16
Q

________ contains 28% amylose and 62% amylopectin

A

Regular corn starch

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17
Q

Starch is readily isolated from the plant source by ______, then centrifuged out of solution and dried

A

wet milling

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18
Q

Isolated starch produces a _________ composed of discrete starch granules

A

dry white powder

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19
Q

Each starch granule is made up of ______ amylose and amylopectin tightly bound and held together by _____ bonding between the polymers

A

anhydrous

hydrogen

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20
Q

Heating in the presence of moisture breaks the ________ bonds,
leading to ________.

A

hydrogen

gelatinization

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21
Q

Swelling of the granule is due to the adsorption of ______, which is facilitated by _____

A

water

heat

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22
Q

The swelling of starch granules increases ________, and breaks________

A

kinetic energy

hydrogen bonds

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23
Q

During gelatinization, starch granules are ______ as ____ molecules access the __ groups on the polymer

A

hydrated
water
OH

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24
Q

Gelatinization temperature is a function of the _______

A

starch source

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25
Q

_________ occurs between 60-70oC

A

Loss of granular integrity (gelatinization)

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26
Q

When the granules have swollen extensively, the viscosity of the solution (increases/decreases) drastically, which is called ________

A

increases

pasting

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27
Q

If the swollen granule solution is stirred, the granules will break up and disperse to form __________

A

a colloidal solution

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28
Q

If the concentration of starch is high during gelatinization, it will form a ____ upon _____

A

gel

cooling

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29
Q

If the concentration of starch is high during gelatinization, it will form a ____, and not a _____

A

viscous solution

gel

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30
Q

What are the factors that influence the gelatinization of starch?

A
  • Concentration
  • Amylose/amylopectin
  • Average molecular weight of the starch
  • Rate of cooling
  • Presence of other components
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31
Q

________ is a linear polymer that tends to form a long thin helical filament-like structure in solution.

A

Amylose

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32
Q

______ has very low solubility as it readily hydrogen bonds to neighboring polymers to form large aggregates that precipitate out of solution.

A

Amylose

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33
Q

On its own, _______ is useless functionally in food systems as it is effectively insoluble.

A

amylose

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34
Q

________ is a highly branched water-dispersible macromolecule.

A

Amylopectin

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35
Q

_________

forms a viscous solution; branching produces a tangled net-like web in solution.

A

Amylopectin

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36
Q

In the presence of ________, which acts like a cross-linking agent, a three- dimensional gel can form, entrapping ______.

A

amylose

water

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37
Q

A gel forms when the kinetic energy of the system is (increased/reduced) sufficiently to allow random _________ to re-form

A

reduced

hydrogen bonds

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38
Q

The extensively hydrogen bonded starch molecules trap ______ within the matrix formed, producing a _____.

A

water

gel

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39
Q

Starch gels become _______ with time - a generally undesirable aspect of starch behavior in food systems

A

firmer

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40
Q

What is the cause of retrogradation?

A

Continued hydrogen bond formation between starch molecules

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41
Q

What are the two problems caused by retrogradation?

A

1) Texture changes

2) Syneresis

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42
Q

What is syneresis?

A

When a gel tightens up so much that it starts to exude water

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43
Q

________ commonly causes starch gels to become more opaque with time.

A

Retrogradation

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44
Q

___________ is one of the key processes responsible for the staling of bread and stiffening of pie fillings.

A

Retrogradation

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45
Q

Normal ____ starch (about 28% amylose) will set to a rigid (transparent/opaque) gel.

A

corn

opaque

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46
Q

Starch from ________, which is a genetically modified low- amylose corn (almost devoid of amylose), will not form a gel at all.

A

waxy maize

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47
Q

_______ does not contain amylose

A

waxy maize

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48
Q

______ starch (~23% amylose) and ______ starch (~28% amylose) form reasonably stable gels that tend to maintain their clarity and do not stiffen appreciably with time

A

Potato

tapioca

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49
Q

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

A

molecular weight

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50
Q

______ tend to retard gel formation and retrogradation

A

Sugars

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51
Q

__________________ tend to inhibit retrogradation and gelation by forming complexes with starch

A

Surface-active agents (surfactants)

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52
Q

Surfactants are most noticeable with ___________ starch systems

A

high-amylose

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53
Q

_______ compete for available water and interfere with starch- to -starch hydrogen bonding.

A

Sugars

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54
Q

The pH of most foods lies in the range of ______.

A

4-7

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55
Q

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

A

acidic
viscosity
hydrolysis

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56
Q

_________ processing can affect the final viscosity of starch

A

Thermal

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57
Q

Why does ionic strength have minor effects in starches?

A

Since starches have no ionizable groups

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58
Q

Which two factors have minor effects on starches?

A
  • pH

- Ionic strength

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59
Q

______ are capable of dramatically changing how a starch behaves in terms of gelation and viscosity.

A

Proteins

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60
Q

The interaction with starch and _______ produces a smooth gel known as _______

A

milk proteins

pudding

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61
Q

In North America, most of our starch is derived from ______

A

corn

62
Q

In pre-gelatinized starches, granules are ____________________, which causes them to swell, and are then _______

A

heated below the gelatinization temperature of the starch

drum-dried

63
Q

Pre-gelatinized starches are dispersible in _________ and requires less ___ or ____ to develop viscosity

A

cold water
heat
time

64
Q

A higher amount of ___________ starch is required to attain similar viscosity effects as with an untreated starch.

A

pre-gelatinized

65
Q

_________ starches are convenient for food processors and are used extensively in the food industry .

A

Pre-gelatinized

66
Q

_________ are commonly termed thin-boiling starches.

A

Acid-modified starches

67
Q

Acid-modified starches are produced by holding starch just below its gelatinization temperature in an ______ medium, then it is ______ and ____

A

acidic
neutralized
dried

68
Q

Why is acid used in acid-modified starch?

A

To partially and randomly hydrolyze the glycosidic linkages in the starch granule without breaking up the INTEGRITY of the granule

69
Q

Acid-modified starches are used in _________ manufacture

A

candy

70
Q

__________ produce easy-to-handle low-viscosity fluids that can be poured into molds and will set into a firm gel upon cooling

A

Acid-modified starches

71
Q

Maximum viscosity is normally reached when the granules are ________ extensively but still intact

A

swollen

72
Q

Swollen granules normally break down, but _________ starches are held together chemically so that the swollen granule retains its integrity

A

cross-linked

73
Q

What compounds are used as cross-linking agents?

A
  • Acetic anhydride
  • Citric anhydride
  • Adipic anhydride
74
Q

________ compounds are used as cross-linking agents

A

Anhydride

75
Q

________ compounds can bridge two _______ groups from adjoining polymers, and hold the swollen granule structure together

A

Anydride

hydroxyl

76
Q

The granules swell (more/less) in cross-linked starch

A

less

77
Q

The maximum viscosity is (higher/lower) in cross-linked starch

A

lower

78
Q

_________ are less susceptible to acid hydrolysis

A

Cross-linked starches

79
Q

What is the overall objective of starch derivatives?

A

To reduce polymer-polymer hydrogen bonding via steric hindrance or the introduction of charged groups

80
Q

What are starch derivatives used to?

A
  • Control retrogradation and staling
  • Improve freeze/thaw stability
  • Reduce textural and opacity changes
81
Q

Starch derivatives are formed by introducing _________ or ________ into the granules

A

hydroxypropyl

acetyl

82
Q

In starch derivatives, _________ prevents the polymers from associating as readily as in natural starch

A

steric hindrance

83
Q

________ can be added to produce starch derivatives, which increase stability against retrogradation because of their _______

A 
Orthophosphate
charge (like charges repel)
84
Q

What other types of new groups can be introduced in a starch?

A
  • Ester
  • Ether
  • Acetyl
85
Q

Give an example of a specialty derivative?

A

Introduction of hydrophobic side chains enables starches to be used as emulsifiers and emulsion stabilizers

86
Q

_____ is used to oxidize a portion of the _______ groups to _______ groups in starches

A

Sodium hypochlorite (NaOCl)
hydroxyl
carboxyl

87
Q

Which groups may be introduced in oxidized starches?

A

Aldehyde and ketone groups

88
Q

The solubility of oxidized starches is _____ dependent

A

pH

89
Q

What is the advantage and the disadvantages of oxidized starch?

A

Advantage: stabilized against retrogradation
Disadvantage: more susceptible to variations in pH and ionic strength in a food product

90
Q

What are the two basic types of starch conversions?

A

1) Dry pyroconversion

2) Acid hydrolysis

91
Q

_________ is used for the production of cold-water-soluble starches

A

Dry pyroconversion

92
Q

___________ is used for wet conversion

A

Acid hydrolysis

93
Q

Acid hydrolysis may be used for the production of _______ or as a preliminary step in the production of ______ from ______

A

dextrins
sugars
starch

94
Q

In pyroconversion, starch granules are sprayed with dilute ______ and subjected to relatively (high/low) temperatures

A

HCl

high

95
Q

Which four reactions may take place in pyroconversion?

A

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)

96
Q

__________ is the breaking of 1,4-linkages and the formation of other linkages, generally random in nature (1,3 or 1,5)

A

Transglucosidation

97
Q

What are the three products formed by pyroconversion?

A

1) White dextrins
2) Yellow dextrins
3) British gums

98
Q

_________ dextrins are soluble in cold water

A

White

99
Q

_________ from pyroconversion can be controlled to produce desired ranges of viscosity

A

White dextrins

100
Q

In pyroconversion, under conditions of high moisture, high acid, and relatively low temperature, hydrolysis predominates, and _________ are formed

A

white dextrins

101
Q

In pyroconversion, under low moisture, moderate acid, and higher temperatures, _______ are formed

A

yellow dextrins

102
Q

The color of yellow dextrins is due to the ______________ reaction

A

non-enzymatic browning (caramelization)

103
Q

In pyroconversion, the viscosity and degree of polymerization of __________ can be controlled

A

yellow dextrins

104
Q

In pyroconversion, _______________ are produced under conditions with little or no acid used, and higher temperatures

A

British gums

105
Q

The pyroconversion products ___________ are dark in color with little hydrolysis and much ore transglucosidation

A

British gums

106
Q

The pyroconversion product _________ is much more viscous and capable of forming a stiff gel; used extensively in candy manufacture

A

British gums

107
Q

Over half of the isolated starch produced is converted to ______ and ______.

A

syrups

sugars

108
Q

___________ is commonly a preliminary step in the conversion of starch to syrups and sugars.

A

Acid hydrolysis

109
Q

In acid hydrolysis, starch is ________ and hydrolyzed in the presence of ______ and pressurized steam

A

gelatinized

HCl

110
Q

Acid hydrolysis is extensive and random, producing ______ and ______

A

dextrins

sugars

111
Q

By controlling acid hydrolysis, the degree of ____________ can be manipulated to a degree to produce glucose syrups of various viscosities and sweetness.

A

dextrinization

112
Q

Starch breakdown can be followed by measuring the ___________ content of the hydrolysate.

A

reducing sugar

113
Q

Reducing sugar content (increases/decreases) with hydrolysis as mono-, di- and oligosaccharides are produced.

A

increases

114
Q

Reducing sugar content is expressed in terms of ______________

A

dextrose equivalents (D.E)

115
Q

If the hydrolysis of starch is 100% complete, then D.E. = ______

A

100

116
Q

What is the equation for D.E?

117
Q

Acid hydrolysis cannot yield dextrose equivalents much beyond ____ since an equilibrium is reached between ________ and ___________.

A

50
hydrolysis
repolymerization

118
Q

__________ is not the best means of producing very sweet, high D.E syrups

A

Acid hydrolysis

119
Q

To obtain syrups that have high D.E., ____________ of gelatinized starch is carried out.

A

enzymatic conversion

120
Q

The enzymes that are capable of hydrolyzing starch are commonly termed _________ - these enzymes are found in most living systems.

A

amylases

121
Q

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.

A

amylases

122
Q

_________ is an endoenzyme - can attack anywhere within the starch
molecule other than the α-1,6 branch point.

A

a-amylase

123
Q

_________ is also known as liquefying enzyme

A

a-amylase

124
Q

__________ causes viscosity of a starch solution to drop rapidly

A

a-amylase

125
Q

Random internal bond breakage (increases/reduces) the overall molecular weight of starch, which is done by _________

A

reduces

a-amylase

126
Q

The end-products of the __________ enzyme are mainly oligosaccharides together with some glucose, maltose, and pannose

A

a-amylase

127
Q

_________ is a trisaccharide containing the α- 1,6 branching linkage

A

Pannose

128
Q

________ is an exoenzyme that attacks the non-reducing end of the starch
chain.

A

B-amylase

129
Q

__________ produces _________ by hydrolyzing the a-1,4 bond every two glucose units over

A

B-amylase

maltose

130
Q

_________ is commonly known as a saccharifying enzyme

A

B-amylase

131
Q

__________ develops sweetness rapidly, but viscosity does not change significantly

A

B-amylase

132
Q

__________ are capable of removing single glucose units from the non-reducing end of starch and to split ________ into two glucose units

A

Glucoamylases

maltose

133
Q

Glucoamylases act from the __________ end of the starch, to split __________ into two glucose units

A

non-reducing end

maltose

134
Q

Combined action of α- and β-amylase and glucoamylase leaves ‘limit _______” - largely the trisaccharide ________.

A

dextrins

pannose

135
Q

___________ hydrolyzes a-1,6 glycosidic linkages

A

Pullulanase

136
Q

_________ attacks the branch points so that the trisaccharide pannose can be broken down to _______ and ________

A

Pullulanase
glucose
maltose

137
Q

a-amylase, B-amylase, glucoamylase, pullulanase brovide a means of converting starch to predominantly __________ (______), which produces syrups with a (high/low) D.E.

A

D-glucose
dextrose
high

138
Q

At D.E. > 90, _________ can be crystallized out of solution and obtained in pure form in a manner very similar to sucrose refining.

A

glucose

139
Q

________ is a useful sweetener, but not as sweet as sucrose.

A

Glucose

140
Q

D-glucose is isomerized to D-

fructose using _____________.

A

glucose isomerase

141
Q

________ has about 1.3 times the sweetening power of glucose

and is somewhat sweeter than sucrose.

A

D-Fructose

142
Q

Glucose isomerase is capable of converting about ____% of D- glucose into D-fructose.

A

45

143
Q

High-fructose corn syrups are similar to ________ and are in direct competition with ________.

A

invert sugars

sucrose

144
Q

Sucrose is commonly inverted using the enzyme __________ to stabilize its sweetness in _________ environments

A

invertase

acidic

145
Q

Why is sucrose inverted?

A

Glycosidic link in sucrose is acid labile, and readily hydrolyzed by heat or acid

146
Q

For acidic beverages, sweetness can be stabilized by ________

A

inversion

147
Q

The term ‘”inverted” refers to the change in the specific rotation of ________________ by a sucrose solution

A

plane-polarized light

148
Q

In a fully converted solution, the direction of rotation is _________

A

inverted (from +66.5o to -39o)

149
Q

Why does high-fructose corn syrup have great value?

A

1) Sweeter than glucose
2) More soluble
3) Does not crystallize readily

150
Q

High-Fructose Corn Syrup becomes sweeter with (increasing/decreasing) temperature

A

decreasing

151
Q

Why does HFCS not crystallize readily? What is this good for?

A
  • Because it is a mixture of sugars

- Good for frozen products

152
Q

____________ have made large inroads into the sucrose market and made the sweetener industry more competitive.

A

High-fructose corn syrups

2) Food Chemistry I (31 decks)

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