Carbohydrates Flashcards
1
Q
What is the general formula for COH’s?
A
Cx(H2O)x
2
Q
What is the molecular formula of most common monosaccharides?
A
C6H12O6
3
Q
What bond links disaccharides?
A
glycosidic
4
Q
Maltose is a common….
A
enzymatic hydrolysis product of starch
5
Q
What do we commonly use sucrose as on a daily basis?
A
Table sugar
6
Q
Lactose is the major sugar in what?
A
Cow’s milk
7
Q
How many monosaccharides are oligosaccharides made up of? Linked together by what type of bonds?
A
3-10, glycosidic bonds
8
Q
What is an example of a trisaccharide? What are its 3 monomers?
A
Raffinose- galactose, glucose, fructose
9
Q
Maltose =
A
glucose + glucose
10
Q
Sucrose =
A
Glucose + fructose
11
Q
Lactose =
A
glucose + galactose
12
Q
What is an example of a tetrasaccharide? What are its 4 monomers?
A
Stachyose - glucose + fructose + galactose + galactose
13
Q
How many monomers do polysaccharides have?
A
> 10
14
Q
What are 5 examples of polysaccharides found in nature?
A
- starch
- cellulose
- glycogen
- pectin
- xanthan gum
15
Q
What are 4 common roles of carbohydrates in living systems?
A
- An energy source in seeds - starch for germination
- Structural component - cellulose and hemicellulose
- A ready supply of energy - mono- and disaccharides
- short-term energy supply for muscles - glycogen
16
Q
What are 3 functions of mono- and disaccharides in foods?
A
- Sweetening agents
- Coloring agents (caramel color)
- Production of flavors (caramelization/Maillard reaction)
17
Q
What are 7 functions of polysaccharides in foods?
A
- Tickening agents
- water-holding/binding agents
- Anticaking agents
- Gelling agents
- Emulsion stabilizers
- For producing edible films
- To encapsulate flavors
18
Q
In addition to having multiple alcohol functional groups, they have either a _______ or an _______ functional group (in their linear form).
A
ketone
aldehyde
19
Q
How is the carbon chain of monosaccharides numbered?
A
from the aldehyde (C-1) or the ketone (C-2) functional group down
20
Q
What is the smallest monosaccharide?
A
Glyceraldehyde (C3)
21
Q
For glyceraldehyldes, the D or L isomerism refers to the ________ carbon.
A
Asymmetric C
22
Q
For other sugars, D or L isomerism refers ONLY to the _____________ and not any of the other asymmetric carbons that may be in the chain.
A
- n-1 carbon (2nd from the bottom)
23
Q
Optical isomers involving asymmetric carbons other than the carbon at the n-1 position are considered ________ or _______
A
different sugars
epimers
24
Q
All C6 monosaccharides are epimers of ______. Examples?
A
Glucose
Ex: D-mannose is a C-2 epimer of D-glucose
25
Monosaccharides can be classified on the basis of _______ and _______.
Carbon number
Functional group
26
What type of compound is a ketohexose? Aldohexose? Aldopentose?
C6 ketone
C6 aldehyde
C5 aldehyde
27
Cyclization is due to the formation of internal ______ and _______
hemiacetals
| hemiketals
28
Are the reactions involving the cyclization of monosaccharides intermolecular or intramolecular?
Intramolecular - the aldehyde or ketone group and the alcohol group are in the same molecule
29
What compounds make up hemiacetals?
Alcohol + aldehyde
30
What compounds make up hemiketals?
Alcohol + ketone
31
What type of ring does a Hemiacetal formation in glucose lead to?
Pyranose ring
32
What type of ring does a Hemiketal formation in fructose lead to?
Furanose ring
33
Cyclization results in an additional ___________ at the ____ position, termed the _________, leading to two optical isomers.
- ASYMMETRIC CARBON
- C1
- "ANOMERIC" CARBON
34
The cyclic form in which the OH group at the anomeric carbon is on the same side of the ring as C6 is termed ___.
β
35
The cyclic form in which the OH group at the anomeric carbon is on the opposite side of the ring is termed ___.
α
36
The crystalline forms of simple sugars is always ________.
Cyclical
37
In a solution containing a simple sugar, there is a dynamic equilibrium between what? How can this effect be observed?
The 3 forms α, β and open chain
by following the optical rotation of plane-polarized light by a solution of the sugar
38
When pure α-D-glucopyranose is dissolved in water, the optical rotation starts at ___ degrees and gradually changes to ___ degrees .
112
| 53
39
When the pure β form is dissolved in water, the optical rotation starts at __ degrees and gradually changes to __ degrees.
19
| 53
40
What is mutarotaion?
The change in the optical rotation because of the change in the equilibrium between two anomers, when the corresponding stereocenters interconvert. In cyclic sugars, mutarotation occurs as α and β anomeric forms interconvert.
41
Mutarotation is the result of what?
Of the cyclic form opening up and recycling, coming to equilibrium with its anomer.
42
What is the mutarotation equilibrium for glucose?
- 62% β-D-glucopyranose
- 37% α-D-glucopyranose
- only 1% in the open-chain form with the active aldehyde group.
43
For fructose (a ketohexose), why is the mutarotaion equilibrium harder to reach?
B/c cyclization via formation of a hemiketal can produce either a five-membered furanose ring or a six-membered pyranose ring.
44
The aldehyde group present on ALDOSES has strong ______ power.
reducing
45
What are aldehydes capable of doing to metal ions? In what type of reaction?
Reducing them. In an oxidation reduction reaction that converts the aldehyde to a carboxylic acid.
46
As a group, the monosaccharides are generally termed _________ and can be tested for and quantitated by specific oxidation/reduction reactions.
"reducing sugars"
47
What is the most common test for reducing sugars?
Fehling's test
48
Fehling’s test involves the reduction of ___ in the form of ________ to ______.
Cu(II)
copper tartrate
Cu(I) oxide
49
Fehling's reagent only reacts with what?
The open-chain form of free aldehyde groups. (only 1% of the sugar is in the open-chain form)
50
Why is fructose still a reducing sugar even though is has no aldehyde group?
Due to ENOLIZATION which converts fructose to glucose, which is then capable of reacting with the Fehling's solution
51
Under what conditions is the reducing power of a sugar lost?
When the OH at the anomeric carbon of the cyclic form is covalently bonded to another group - this prevents the ring from opening
52
What does the conversion to the open-chain form require of the OH group bound to the anomeric carbon?
It requires that the OH group revert back to an aldehyde group
53
Is the disaccharide maltose a reducing sugar?
yes
54
Is the disaccharide sucrose a reducing sugar?
No
55
What is the bond between the two monomers in maltose?
alpha-1-4-glycosidic
56
What is the bond between the two monomers in sucrose?
alpha-1-2-glycosidic
57
What makes sucrose a non-reducing sugar?
The fact that both of its anomeric carbons (C1 of glucose and C2 of fructose) are tied up in the glycosidic bond
58
What is the reducing power of maltose relative to glucose?
it has half the reducing power of glucose b/c one of the 2 anomeric carbons is used in the glycosidic bond
59
Why is maltose capable of ring opening at one end of the molecule?
Because the anomeric C of the 2nd glucose is not involved in the glycosidic bond
60
Can ring opening occur at one end of a sucrose molecule?
No
61
What type of reactions are the basis of caramelization and the Malliard reaction?
Dehydration reactions
62
Dehydration reactions can take place at temperatures below ____ and in _____solutions but they occur _____.
100 C
dilute
very slowly
63
At what temperature/pH do dehydration reaction become prevalent when concentrated sugar solutions are heated?
130 C
Very acidic conditions - pH<2.2
64
What happens chemically as concentrated sugar solutions are heated?
Water evaporates allowing molecular dehydration and oxidative fission to take place, leading to a breakdown of the C-chain into smaller units (flavor compounds)
65
In what 2 ways can water be eliminated from sugar molecules?
1. loss of water from 2 sugar molecules via reaction of their hydroxyl groups: R-OH + OH-R --> R-O-R + H2O
2. Elimination of water from within a sugar molecule, leading to the formation of highly unsaturated ring structures
66
What does the loss of water from 2 sugar molecules via reaction of their hydroxyl groups result in? Is this the predominant reaction?
Random polymerizaion
No
67
A common intermediate formed during caramelization reactions by dehydration is __________.
hydroxymethylfurfural (HMF)
68
What do fragmentation reactions of highly unsaturated ring structures produce? What are some of the products of these reactions when isolated under alkaline conditions?
What can many of the highly unsaturated ring structures and their breakdown products (short-chain aldehydes, ketones and carboxylic acids) do?
Low-molecular-weight, unsaturated, and reactive compounds.
Products: Acetol, Diacetyl, Acetoin
They can polymerize
69
What do extensive dehydration reactions eventually lead to?
The formation of an amorphous, charged brown pigment - caramel
70
What are browning reactions associated with?
Decay processes
71
What two categories can browning reactions be classified into?
1. Oxidative browning
| 2. non-oxidative browning
72
What is oxidative browning associated with?
Browning of plant tissues
73
What enzyme is responsible for oxidative browning reactions? What does it do?
polyphenol oxidase (PPO)
Oxidizes mono- or dihydroxy phenols into quinones
74
Quinones are quite reactive and can react _______ to polymerize into a ________.
non-enzymatically
brown pigment
75
What 2 enzymes are indirectly associated with browning? What do they produce/supply?
ascorbic acid oxidase, lipoxygenase
Produce reactive carbonyl compounds that can undergo non-enzymatic browning
76
What are the two types of non-enzymatic/non-oxidative browning?
1. sugar-sugar reaction (caramelization reactions)
| 2. sugar-amine reactions (maillard reactions)
77
When do caramelization reactions occur?
When any concentrated sugar reaction is heated
78
The caramelization reaction is used commercially to produce what two characteristics?
1. flavor - caramel syrup
| 2. caramel color
79
What are caramel flavors generally made from?
Concentrated sucrose solutions
80
What is caramel color generally made from?
glucose syrup
81
What are the two main types of reactions that happen during caramelization? What is produced as a result?
dehydration, polymerization
Produce high-molecular-weight water-soluble polymers that are very dark in color
82
What are 3 characteristics of the polymers that are formed as a result of the dehydration and polymerization that occurs during caramelization?
1. high-molecular-weight 2. water-soluble polymers
| 3. very dark in color (high tinctorial power)
83
What are examples of foods that have developed a caramel color?
Baking, beer, soft drinks, whiskey, soy sauce
84
What is the malliard reaction?
The reaction of reducing sugars with primary AMINES, generally AAs and proteins
85
What foods are a result of the maillard reaction?
coffee flavor, color and aroma, roasking popcorn, roasting peanuts, cashews baked bread aroma
86
What is the first reaction in a maillard reaction? What does this produce? What is formed right after?
the condensation of a primary amine and a reducing sugar to form a Schiff base followed by formation of an Amadori compound
87
________ compound is key intermediate in Maillard reaction comparable to HMF in caramelization.
Amadori
88
The overall process of converting from the initial Schiff base to an Amadori compound is termed____________
Amadori rearrangement.
89
What can the amadori molecule lose?
Water from within the molecule
90
At what stage in the maillard reactioon can different paths be taken depending on environmental conditions?
Once the amadori molecule has been produced
91
What major reactions happen in malliard reactions at high tempuratures?
dehydration and fragmentation
92
What do the end products contain in their structure after undergoing the maillard reactions at high temps? Why?
Contain nitrogen in their structures b/c there is an amine group attached to the sugar
93
What is a subcomponent of the Maillard reaction.
Strecker degradation
94
Strecker degradation is the reaction of __________ with the ___________ produced by either the Maillard reaction or caramelization reactions.
1. free AAs
| 2. bicarbonyl intermediates
95
What 4 products are formed after strecker degradation? What is special about these compounds?
CO2, ammonia, formaldehyde, pyrasines.
All contribute to the aroma of roasted foods
96
What 2 compounds in strecker degradatoin give rise to strong odours?
aldehydes and aminoketones
97
After strecker degradation, what aroma does ethanal give off? Methylpropanal? 2-phenylethanal?
1. fruity, sweet
2. malty
3. flowery/honey like
98
What can the condensation of two aminoketones yeild?
pyrazine derivatives - powerful aroma compounds
99
Strecker degradation reactions are used commercially to produce what?
artificial flavor compounds
100
1 , 2 , and 3 represent an important group of reactions associated with food color and flavor.
1. Caramelization
2. the Maillard reaction
3. Strecker degradation
101
Why is the evaluation of sweetness difficult?
Because it's a SUBJECTIVE response (no instrument to measure it)
102
Rank 6 sugars from least sweet to most sweet...
Lactose (39), maltose (46), invert (65), xylose (67), glucose (69), sucrose (reference) (100), fructose (114)
103
What is invert sugar?
sucrose hydrolyzed to a mixture of glucose and fructose.
104
What causes sweetness to decrease? Why?
Increasing temp. Because this changes the relative concentration of openchain, alpha and beta forms which all differ in sweetness
105
What tends to heighten sweetness?
alcohol!!! WOOHOO!!!
106
How does the sweetness of sugars differ when they are mixed together than when tasted separately?
Sweeter when mixed
107
What is the saturation point of lactose?
20%
108
What is the saturation point of maltose?
40%
109
What is the saturation point of glucose?
60%
110
What is the saturation point of sucrose?
70%
111
What is the saturation point of fructose?
85%
112
________ is a very important criterion when high sugar concentrations are required to inhibit microbial growth.
Solubility
113
What can happen if the solubility of sugar is too low?
Crystalizaiton, making the texture grainy
114
What common method is used to avoid/inhibit sugar crystalization?
mix 2 sugars together
115
What does sugar bind to which makes it unavailable for microorganisms? Why? What foods exemplify this?
water - lowers Aw of system
Pectin gels in jam/jellies
116
How can browning me minimized during baking?
sucrose
117
To help color development in meat curing, what is used to prevent the oxidation of meat pigments?
reducing sugars
118
What are 3 other uses of sugars?
1. humectants
2. flavor binding agents
3. viscosity enhancers
119
How are sugar alcohols commercially produced?
By reducing the aldehyde group to a hydroxyl group by hydrogenation
120
Sugar alcohols are only absorbed by _______ diffusion, thereby contributing _____ calories than sugars.
passive
fewer
121
What is the relationship between sugar alcohols and dental caries?
Sugar alcohols are poorly metabolized by the microbial flora of the mouth – do not contribute to dental caries (which are caused by the acids produced by the microflora from the fermentation of sugars).
122
What are the 2 most common sugar alcohols? What is their relative sweetness?
sorbitol (51), mannitol (54)
123
Are sugar alcohols as sweet as sugars? Which sugar alcohol is an exception?
no
Xylitol - comparable in sweetness to sucrose!!
124
What is xylitol?
a sweet sugar alcohol
125
What can xylitol be produced from? What is this a polymer of? Where is this widely found?
Xylan, a polymer of xylose, widely found in nature
126
What are 4 examples of foods found in nature that contain xylitol? What % of their dry weight is xylan?
birch tree chips, almond and pecan shells, cottonseed hulls, corn cobs
20-25%
127
How is xylan converted to xylitol commertially? What are two other ways to produce xylitol?
Xylan is hydrolyzed to xylose and hydrogenated using a nickel catalyst to produce xylitol.
Other approaches:
- use yeast via fermentation of xylose
- enzymatic conversion of glucose
128
In what 2 ways are sugar alcohols used extensively by the food industry?
1. bulking agents/viscosity enhancers in artificially sweetened products to provide "body"
2. water-binding agents to plasticize intermediate-moisture foods and reduce the water activity of the food system without adding excessive sweetness
129
What are the 3 most common polysaccharides?
starch, cellulose, pectin
130
The properties of polysaccharides are a function of what 3 things?
1. sugar/chemical makeup
2. the presence of unique functional groups
3. molecular weight and degree of branching
+ combination of the 3
131
What are 2 examples of seed gums?
guar gum, locust bean gum
132
What are 2 examples of plant exudate gums?
gum arabic. gum tragacanth
133
What are 2 examples of seaweed gums?
agar, carrageenan
134
What are 2 examples of microbial gums?
dextran, xanthan gum
135
What is the most abundant form of stored carbohydrate available on Earth, other than cellulose?
starch
136
What is the purpose if starch in plants?
An energy store for seed germination
137
What is the main source of dietary COH?
starch
138
What 4 staple foods are high in starch?
potatoes, rice, corn, wheat
139
What is starch exclusively made up of?
D-glucose
140
What two fractions is starch made up of?
Amylose, amylopectin
141
What is amylose?
D-glucose long linear polymer linked by α-1,4 glycosidic bonds
142
What is amylopectin?
Branched polymer of D-glucose linked by α-1,4 glycosidic bonds & α-1,6 glycosidic bonds at branching points
143
How is starch found in most plant sources?
hard, water-insoluble granules
144
Each starch source contains amylose and amylopectin in __________ predetermined ratios
predetermined
145
What % of regular corn starch is amylose? Amylopectin?
28% amylose
| 62% amylopectin
146
What % of waxy maize is amylose? Amylopectin?
almost 100% amylopectin
147
How is starch isolated from the plant source?
Via wet milling, then centrifuged out of solution and dried
148
What does the isolation of starch from plant sources produce?
dry white powder composed of discrete starch granules
149
What happens to starch when heated in the presence of moisture?
They gelatinize
150
What happens molecularly during gelatinization?
Granule slowly swells due to water absorption via heat. Increasing kinectic energy break H-bonds and the granules slowly hydrate as water molecules access the OH groups of the polymer
151
Loss of granular integrity generally occurs between...
60-70 C
152
gelatinization temperature is a function of the ______ source.
starch
153
What happens in terms of viscosity of the solution once the granuels have swollen a lot? What is this called?
Viscosity increases drastically
Pasting
154
What happens if a highly viscous (paste) starch solution is stirred?
the granules break up and disperse to form a colloidal solution
155
If the concentration of starch is high, it will form a _______ upon cooling. At lower concentrations, one may obtain a viscous solution that does not form a _____.
gel
156
What are variable that affect gelatinization of starch?
1. [starch]
2. amylose:amylopectin ratio of the starch
3. avg. molecular weight (chain length) of starch
4. rate of cooling
5. other components in solution
157
Amylose is a _______ polymer that tends to form a long thin _______ filament-like structure in solution.
linear
helical
158
Does amylose have high or low solubility?
very low
159
Why is amylose useless functionally in food systems?
insoluble
160
Amylose readily ______ bonds to neighboring polymers to form large ________that _______out of solution.
hydrogen
aggregates
percipitate
161
What is amylopectin?
a highly branched water-dispersible macromolecule
162
What does amylose act as in the presence of amylopectin?
a cross-linking agent
163
What can form when amylose is in the presence of amylopectin?
a 3D gel which traps water
164
A gel forms when the __________ of the system is reduced sufficiently to allow random hydrogen bonds to re-form - the extensively hydrogen bonded starch molecules trap water within the matrix formed, producing a gel.
kinetic energy
165
What is one undesirable aspect of starch behavior in food systems?
starch gels become more firm with time
166
What is retrogradation due to?
the continued H-bond formation between starch molecules
167
What 2 problems arise in retrogradation?
1. texture of the gel changes over time = undesirable
| 2. syneresis
168
What is syneresis?
when gel tightens up so much that it starts to exude water
169
Retrogradation commonly causes starch gels to become more ______ with time.
opaque
170
Retrogradation is one of the key processes responsible for the ______ of bread and _______of pie fillings.
staling
stiffening
171
What does normal corn starch settle to become during retrogradation?
a rigid opaque gel
172
What is special about starch from waxy maize? Why?
Will not form a gel. It is a genetically modified low amylose corn
173
_______ starch (~__% amylose) and _______ starch (~__% amylose) form reasonably stable gels that tend to maintain their clarity and do not stiffen appreciably with time. Why?
Potato 23%
tapioca 28%
Because of their high avg. molecular weight making them much less mobile - H-bonds continue to develop between them over time but just at a reallllllly slow rate
174
How do sugars retard gel formation and retrogradation?
They compete for available water and interfere with starch-to-starch H-bonding
175
What do surface-active agents (surfactants) inhibit? How?
Inhibit retrogradation and gelation by forming complexes with starch
176
What is the pH range of most foods?
4-7
177
At pH 4-7, pH affects the behavior of starches only in a minor way because the natural starches are _______.
uncharged.
178
How can highly acidic foods affect starch?
reduce viscosity
179
Why does ionic strength, like pH, only have minor effect on starches?
Because starches have no ionizable groups
180
______are capable of dramatically changing how a starch behaves in terms of gelation and viscosity.
Proteins
181
What does the interaction of starch with milk proteins produce?
pudding
182
In North Am., most of our starch is derived from ______.
Corn
183
What are pre-gelatinized starches heated to relative to the generalization temperature of the starch? What does this cause the starch granuels to do?
below gelatinization temp. Causes granules to swell
184
Pre-gelatinization causes some __________ of the starch granule - making it ________ in cold water and requires _______ heat or time to develop viscosity.
disorganization
dispersible
less
185
How much of a pre-gelatinized starch is required to attain similar viscosity effects than an unstreared starch?
You need a high amount of pre-gelatinization starch
186
What are acid-modified staches commonly termed?
thin-boiling starches
187
How are acid-modified starches produced?
by holding starch just below its gelatinization temperature in an acidic medium - then neutralized and dried
188
What is the acidity used for in Acid-Modified starches?
It partially and randomly hydrolyze the glycosidic linkages in the starch granule without breaking up the integrity of the granule
189
What type of starches are used in candy manufacture? What type of fluids do they produce?
Thin-boiling starches.
| Produce easy-to-handle low-viscosity fluids that can be poured into molds and will set into a firm get upon cooling
190
What is another name for starch gum candies?
jujubes
191
What is the purpose of cross linking starchs?
To chemically hold starch granules together so that swollen granule retains its integrity
192
What 3 things are typically used as cross-linking agents? How do these hold the swollen granule structure together?
Acetic anhydrides, citric anhydrides, adipic anhydrides.
By bridging 2 hydroxyls from adjoining polymers
193
What is the net result of cross-linking starches in terms of swelling and integrity?
the granules will swell somewhat less but will maintain their integrity
194
What is the resulting viscosity of cross-linking starches relative to the origional starch?
lower viscosity but much more resistant to shear
195
Cross-linked starches are less susceptible to __________as the cross-links make up for some of the bonds broken by the action of ______.
acid hydrolysis
acid
196
What 3 things are starch derivatives used to do?
1. control retrogradation and staling
2. improve freeze/thaw stability
3. reduce textural and opacity changes
197
What is the overall objective of starch derivatives)
reduce the polymer-polymer hydrogen bonding via steric hindrance or via introduction of charged groups (hydroxypropyl / acetyl) into the starch granule
198
What does steric hindrance prevent polymers from doing?
prevents polymers from associating as readily as in natural starch
199
The addition of hydrophobic side chains can enable starches to be used as what ?
Emulsifiers and emulsion stabilizers
200
To form oxidized starches, ___________ is used to oxidize a portion of the hydroxyl groups to ______ groups. How does this alter the starch? What does this do?
sodium hypochlorite (NaOCl)
carboxyl
Starch is now charged
201
What are oxidized starches stabilized against? But what are they more suseptible to?
retrogradation
variations in pH & ionic strength in a food product
202
What is the solubility of oxidized starches dependent on?
pH
203
What are the 2 basic types of oxidized starches?
1. dry pyroconversion
| 2. acid hydrolysis
204
What are the dry pyroconversion type of oxidized starches used for the production of?
cold-water-soluble starches
205
What are the acid hydrolysis type of oxidized starches used for the production of?
dextrins via wet conversion or as a preliminary step in the production of sugars from starch
206
During pyroconversion, Starch granules are sprayed with dilute ______ and subjected to relatively _____ temperatures. What 4 reactions may take place under these conditions?
HCl
high
1. Hydrolysis of the α-1,4 and α-1,6 linkages
2. Transglucosidation - breaking of 1,4-linkages and the formation of other linkages, generally random in nature, i.e. 1,3 linkage, 1,5 linkage, etc
3. Repolymerization - any free sugars produced can repolymerize
4. Caramelization - any free sugars produced can undergo the caramelization reaction
207
What 3 basic products can be produced by pyroconversion?
1. white dextrins
2. yellow dextrins
3. british gums
208
Under what conditions does hydrolysis predominate in the production of white dextrins ?
high moisture, high acidity, relatively low tempurature
209
Are white dextrins soluble or insoluble in water?
soluble
210
What are the 3 conditions of yellow dextrins?
lower moisture, moderate acid, higher tempurature
211
What is the yellow color of yellow dextrins due to?
the non-enzymatic browning reaction - caramelization
212
What can be controlled in the production of yellow dextrins?
viscosity and degree of polymerization
213
What tempurature and acidity is used in the production of british gums?
- little/no acid
| - high temp
214
What color are british gums?
dark
215
What is british gum used extensively for the production of? Why?
candy - very viscous and capable of forming a stiff gel
216
What is over half of the isolated starch produced converted to?
syrups & sugars
217
_______ is commonly a preliminary step in the conversion of starch to syrups and sugars.
Acid hydrolysis
218
During acid hydrolysis, starch is gelatinized in the presence of what? What two things happen simultaneously?
hydrolytic acid, pressurized steam
While the starch gelatinizes, it is simultaneously hydrolyzed by the acid.
219
what does starch hydrolysis produce?
dextrins and sugars
220
What is reducing sugar content expressed in terms of?
dextrose equivalents (D.E.)
221
D.E. =
[(RP/g of syrup)/(RP/g of dextrose)](100)
222
What does D.E. = if the hydrolysis of starch is 100% complete?
D.E. = 100
223
Acid hydrolysis cannot yeild dextrose equivalents much beyond what number? Why?
50 because an equilibrium is reached between hydrolysis and repolymerization
224
__________ is not the best means of producing very sweet, high-D.E. syrups
acid hydrolysis
225
What process is carried out in order to obtain syrups that have high DE?
enzymatic conversion of gelatinized starch.
226
What enzymes are capable of hydrolyzing starch?
amylase
227
Commercially, the sources of amylase enzymes are _________ because relatively large quantities of selective enzymes can be obtained through _____________ and the enzymes are simple to isolate.
microorganisms
| genetic manipulation
228
What type of enzyme is α-Amylase?
An endoenzyme
229
What is an endoenzyme? What is another name for endoenzymes?
an enzyme that can attach anywhere within the starch molecule other than the α-1,6 branch point.
Liquefying enzymes
230
liquefying enzyme - causes ________ of a starch solution to drop rapidly.
viscosity
231
What reduces the overall molecular weight of starch?
Random internal bond breakage
232
What are possible end product of reactions catalyzed by α-Amylase?
mainly oligosaccharides together with some glucose, maltose, and pannose
233
What type of enzyme is β-Amylase?
AN EXOENZYME
234
What does an exoenzyme do?
It attracts the non-reducing end of the starch chain
235
What do reactions catalyzed by β-Amylase produce? How
maltose, by hydrolyzing the α-1,4 bond every two glucose units over.
236
What is β-Amylase commonly known as? Why?
saccharifying enzyme b/c is develops sweetness rapidly
237
What 2 things is the glucoamylase enzyme capable of doing?
remove single glucose units from the non-reducing end of starch, and split maltose into two glucose units
238
What does the enzyme Pullulanase do?
Hydrolyzes α-1,6 glycosidic linkages by attacking the branch points so that pannose (trisaccharide) can be broken down to glucose + maltose
239
α-Amylase, β-Amylase, Glucoamylases, and Pullulanase provide a means of converting starch to predominantly ________.
D-glucose (dextrose)
240
In summary, what do each of these enzymes do?
1. α-Amylase:
2. β-Amylase:
3. Glucoamylase:
4. Pullulanase:
Net result: these enzymes can produce syrups which have a D.E. of ...
1. reduces molecular weight, producing oligosaccharides.
2. produces maltose.
3. converts maltose to glucose.
4. takes care of the branch points.
Net resut: D.E. > 90
241
What can happen to glucose at D.E. > 90?
It can be crystallized out of solution and obtained in pure form in a manner very similar to sucrose refining.
242
What enzyme converts D-glucose to D-fructose?
glucose isomerase
243
How much sweeter is D-fructose than glucose?
1.3 times
244
The production of high fructose corn syrup is carried out on glucose syrups that have a _____D.E. or on _____D-glucose.
high
| purified
245
Glucose isomerase is capable of converting about __% of D-glucose into D-fructose.
45
246
Reason why sucrose is inverted - glycosidic link in sucrose is _____ labile and readily hydrolyzed by _____ or _____- for acidic beverages, sweetness can be ______ by inversion.
Acid
Heat or acid
Stabilized
247
What does the term "inverted" refer to?
to the change in the specific rotation of plane-polarized light by a sucrose solution as it is converted to a mixture of sucrose, glucose, and fructose
248
In a fully converted solution, the direction of rotation is inverted from _____ to _____.
+66.5 degrees to 39 degrees
249
For what 3 reasons does high fructose syrup have great value?
1. intrinsically sweeter than glucose - becomes sweeter with decreasing temp
2. more soluble
3. it does not crystallize readily b/c it is a mixture of sugars (good for frozen products)
250
What is the estimated annual world starch production?
12 million tons
251
What country is the major producer of starch?
USA USA USA - largely corn starch
252
How much of the world starch production does canada produce?
~2% lmao
253
Starch is mainly used for its _______ properties and for production of ________.
texture-modifying
| syrups/sweeteners
254
In acidic foods, __________ starches are used to minimize hydrolysis during heat treatment
cross-linked
255
Why is cellulose indigestible in humans?
lack enzyme capable of hydrolyzing the β-1,4 glycosidic linkage
256
Cellulose exists only in a ______form with no ______counterpart.
linear
| branched
257
What is the durability of cellulose comparable to?
stability of paper / time it takes wood to rot
258
_________cellulose can be used as a bulking agent without contributing calories and is used extensively as a plating agent
Microcrystalline
259
What is Carboxymethyl Cellulose (CMC)? How is it formed?
Methylated derivative of pure cellulose formed by hydrating cellulose in a strongly basic solution and then reacting it with sodium chloroacetate
260
What is the net result of the Carboxymethyl Cellulose (CMC) reaction?
addition of a caboxymethyl group onto the chain
261
What are 3 benefits of the production of Carboxymethyl Cellulose (CMC)?
1. more soluble polymer
2. viscous
3. can create weak gel
262
The presence of carboxyl groups means that CMC is susceptible to _______ and may precipitate out of solution around its __________.
pH changes
isoelectric point
263
Under what condition do the CMC polymers repel each other?
When the pH is above the pKa of the carboxyl groups
264
What is the application of CMCs in the food industry? In what food is it most used?
a no calorie viscosity-enhancing agent
Ice cream :) smooth texture and inhibits crystal growth during storage
265
What are 2 other commercial cellulose derivatives?
hydroxypropyl cellulose & methyl cellulose.
- soluble
- viscosities are not affected by pH or salts b/c non-ionic .
266
What are pectic substances?
polysaccharides associated with the middle lammella between plant cell walls - a complex carbohydrate largely made up of polygalacturonic acid
267
What is the basic unit of pectic substances?
galacturonic acid
268
What are pectic acids?
polymers of predominantly polygalacturonic acid free of methyl ester groups
269
What are pectinic acids?
polymers of polygalacturonic acid with some degree of methylation (low methoxy pectin).
270
What is pectin?
polymers of polygalacturonic acid with >50% of the carboxyl groups methylated
271
Pectin can be quite variable in its degree of __________ depending on the source and on the method of extraction.
methylation
272
The major use of pectin is for the production of ____ and _____ , which use _____ to prevent microbial growth by reducing ______.
Jams and jellies
sugar
water activity
273
What must be present for pectin to form a suitable get? The pH must be in what range? What do these conditions allow?
sugar, acid, water
2.8-3.2
The repulsive force of the residual carboxyl groups is reduced, while the sugar competes for water of hydration, allowing the polymers to associate in a 3D manner forming a gel
274
Although pectin can form a gel without sugar, large amounts are required, making it _______.
uneconomical
275
Most pectin is obtained as a by-product of the ______ industry
citrus
276
What determines the quality and price of pectin?
degree of methylation (DM)
277
Pectin with a DM of ___ serves well for jellies.
~50
278
What pectin DM is required for jam?
> 74
279
Low-methoxy pectin is useful in the manufacture of ______ jams and jellies
diet
280
Low-methoxy pectins are produced by controlled hydrolysis of the methyl groups using either ________ conditions or using the enzyme __________.
alkaline
pectin methyl esterase
281
For diet products to be shelf-stable, _________ agents are generally required to compensate for the osmotic effect (water activity reduction) that is lost when sugar is not used in the product.
antimicrobial
282
Seeds of some plants contain unique polysaccharides called _____.
gums
283
What are 2 important seed gums? Both of these gums are ________.
guar gum
locust bean gum
galactomannans
284
What are galactomannans?
polymers of galactose and mannose consisting of a mannose backbone (β-1,4 linkages)
285
Where is guar gum derived from?
leguminous plant that is widely grown in india and pakistan
286
What is the ratio of mannose to galactose in guar gum?
2:1
a linear chain of Dmannose (β-1,4 linkages) with D-galactose branches (α-1,6 linkage) interspersed roughly every other mannose unit.
287
What is the most important property of guar gum?
its ability to hydrate very rapidly in cold water and form a very viscous solution
288
What is guar gum commonly used in?
instant puddings
289
What is the ratio of mannose to galactose of locust bean gum?
4:1 to 5:1
a linear chain of D-mannose (β-1,4 linkages) with Dgalactose branches (α-1,6 linkage) interspersed roughly every fourth or fifth mannose unit.
290
What food product is locust bean gum used in? Why?
- Ice cream - for smooth meltdown and freeze/thaw resistance
| - Baking industry to produce softer doughs
291
From a functional standpoint, guar gum and locust bean gum are largely _________.
interchangeable
292
What are 3 general properties of guar gum and locust bean gum?
1. viscosity does not change much with pH
2. Stability and rheology are not affected much by processing
3. both compatible with starches, cellulose, and other gums
293
How are Plant Exudate Gums obtained?
by wounding specific tropical trees and shrubs and collecting the exudate
294
What are the 4 main plant exudate gums? These gums are all what?
arabic
ghatti
karaya
tragacanth
All heteropolysaccharides
295
Gum arabic is charged due to the presence of ______.
glucuronic acid
296
What is the distinguishing feature of gum arabic?
it is extremely soluble in water - can make up to 50% solutions
297
What is the major use of gum arabic?
a flavor carrier/dispersant
298
gum arabic is extensively used to inhibit what?
sugar crystalization
299
Gum arabic is used as a thickner in what 3 products?
candies, jellies, chewing gums
300
What are the 3 types of functional polysaccharides of saeweed?
1. irish moss - carrageenan
2. Red algae - agar
3. Giant kelp (brown algae) - alginates
301
What is carrageenan composed of?
D- and L-galactose and 3,6-anhydro-D-galactose units
some galactose moieties are sulfonated
302
What two fractions is carrageenan made up of?
linear and branched
303
Carrageenan has the unique ability to do what?
To complex with milk proteins to form a very light gel
304
How is carrageenan vastly used in terms of chocolate & ice cream?
To suspend insoluble chocolate solids in chocolate milk
To minimize drip in ice cream
305
What is agar derived from?
red algae
306
What type of gel is agar able to form? At what tempurature does this gel set?
thermoreversible
40C
307
What is agar best known for?
Its use in bacteriological media
308
Agar is used as a gelling agent for what 4 products?
1. bakery products
2. confections
3. meat
4. fish
309
What are alginates?
polysaccharides that are obtained from brown algae
310
What are alginates made up of?
linear polymers of D-mannuronic and L-glucuronic acids
311
Presence of ______ groups makes alginates sensitive to _____ and ________ of a food system.
carboxyl
pH
ionic strength
312
Many microorganisms produce "slimes" which are ____________.
extracellular polysaccharides
313
How do dextrans differ from starch in terms of glucose linkage?
Dextrans are polysaccharides made up of glucose that differ from starch because glucose units are linked together by α-1,6, rather than α-1,4 linkages, with α-1,3 linkages at branch points.
314
What is the most common organism used to produce dextran? How does it produce it?
Leuconostoc mesenteroides via fermentation of sucrose
315
Chain length and degree of branching of dextran can be controlled _______.
genetically
316
What is xantha gum? What is it produced by? What is it made up of & in what ratio?
Complex heteropolysaccharide produced by Xanthmonous campestris
Made up of: D-glucose, D-mannose, D-galacturonic acid. 3:3:2 ratio
317
What are the 4 major properties of xanthan gum?
1. excellent heat stability - no change in viscosity with change in temp
2. Viscosity is highly affected by shear, but returns immediately after shear is removed (pseudoplastic)
3. Viscosity is independent of pH
4. Forms a gel with locust bean gum in very low []
318
Xanthan gum is very useful in production of ___________ or gels w/o the need for ______.
instant puddings
heat
