2. Carbohydrates Flashcards
(82 cards)
1
Q
Why are carbohydrates important?
A
2
Q
What are the major sources of carbohydrate containing foods?
A
- Wholegrain foods are major carbohydrate source in the form of starch
- Wholegrain foods, vegetables, legumes and fruits are major carbohydrate source in the form of dietary fibre
- Milk products provide lactose, an important energy source for infants
3
Q
What are the four simple carbohydrates?
A
Glucose
Fructose
Mannose
Galactose
4
Q
What is the chemical formula for the simple carbohydrates (hexoses)?
A
C6H12O6
5
Q
A
6
Q
A
7
Q
Which isomer is which?
A
8
Q
A
9
Q
A
10
Q
What is sucrose? Made up of and sourced from
A
- fructose and glucose
- refined from sugar cane and sugar beets, tastes sweet and is readily available
11
Q
What is lactose made up of and sourced from?
A
- galactose and glucose
- found in milk and milk products
12
Q
What is maltose made up of and sourced from?
A
- two glucose units
- produced during the germination of seeds and fermentation from breaking down starch
13
Q
What is the bond created when maltose is formed?
A
One unit of D-glucose and one unit of D-glucose joined by an A (1,4)-glycosidic bond
14
Q
How is maltose formed from digestion?
A
In digestion formed by pancreatic alpha-amylase action on starch
Digestion by intestinal maltase yields 2 glucose unit for absorption
15
Q
What is the bond in lactose?
A
One unit of D galactose and one unit of D glucose joined by a Beta-1,4 glycosidic bond
16
Q
What is the digestion outcome for lactose?
A
- It is digested by intestinal lactase to give one galactose and one glucose unit for absorption.
- Lactose intolerance comes from individuals lacking lactase or with low lactase activity. Symptoms include bloating, abdominal discomfort, watery stool
17
Q
What is the bond of sucrose?
A
One unit of alpha D-glucose and one unit of beta-D-fructose joined by an alpha(1,2)beta-glycosidic bond.
18
Q
What is the digestion outcome of sucrose?
A
- From juices of sugar cane and sugar beet
- digested by intestinal sucrase to yield one glucose and one fructose
19
Q
Which sugars tend to be sweeter?
A
20
Q
What are some commercial sugars?
A
- Cane sugar
- Beet sugar
- Palm sugar
- Treacle, molasses and golden syrup
21
Q
Where is cane sugar sourced from and what is it used for?
A
22
Q
Where is beet sugar sourced from and what is it composed of?
A
23
Q
Where is palm sugar sourced from and what is the composition?
A
24
Q
What is treacle?
A
Any syrup made in the refining of cane sugar
25
What is molasses?
Molasses is a treacle, by product of the refining of sugar (sucrose) from sugar cane juice. Still contains some left over sugar (sucrose) giving it a mild sweetness but high in phenolic acids and polyphenols that give it a dark brown colour
26
What is golden syrup?
* By product from refining of sugar (sucrose) from sugarcane juice. But the juice has been caramelised to a medium flavour (loss of sucrose) that has acid (usually citric acid from lemons) to prevent further crystallisation.
* Milder version of molasses.
27
What is corn syrup?
Produced by enzymatic degredation of corn starch.
Glucose rich
28
What is high fructose corn syrup?
Produced from corn syrup by enzymatic isomerisation of glucose to fructose.
fructose rich
29
What is inverted sugar?
Produced by enzymatic degredation of sucrose.
Equal ratio of glucose and fructose
30
How are complex carbohydrates defined?
They are multiple glucose units linked together in straight chain or highly branched chain.
Oligosaccharides have less than 20 units while polysaccharides have more.
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Name these
33
What is the glycemic index?
It classifies foods according to their potential for raising blood glucose on consumption of the same carbohydrate from the foods.
As per 50g carbohydrate used
34
How is GI determined for a particular food?
1. Feed 10 or more healthy individuals a food containing 50g carbohydrate
2. Measure blood glucose levels over the next 2 hours
3. Repeat with same individuals but feeding with 50g glucose
35
What foods have high GI and which low GI?
36
What is dietary fibre defined as?
Dietary fibre is that fraction of the edible parts of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine, with complete or partial fermentation in the large intestine.
37
What are the food regulation authorities FSANZ, AOAC, AACC?
38
What is nutritional dietary fibre defined as?
Plant carbohydrates that are resistant to mammalian digestive enzymes
39
What is total dietary fibre defined as by the AOAC?
* Food residue remaining after removal of lipid, protein and starch
* Mainly cellulose and non-cellulosic polysaccharides (NCP)
40
What is funcitonal fibre defined as?
Plant and non plant fibres added to food formulation
41
Where do dietary fibres come from?
From cell wall of plants. Pectin helps bring water in for hydration and build the matrix
42
What is the fibre content like in leaves?
Leaves have high water contents, low cell wall components and virtually no lignin
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What is the fibre content like in fruits?
Have high water contents, low cell walls components and high pectin content
44
What is the fibre content like in legumes?
Legumes have high level of soluble cell walls polysaccharides and non cell wall galacto-oligosaccharides
45
What is the fibre content like for whole grains?
Whole grain cereals have high cell walls polysaccharide that are moderately soluble to insoluble
46
What is the water solubility of cellulose and its function?
Celluose is insoluble
Basic structural material of cell walls
47
What is the water solubility and function of lignin?
Lignin is insoluble
Along with cellulose, forms the woody cell walls of plants
48
What is the water solubility and function of hemicellulose?
It is insoluble and soluble.
It surrounds skeletal material of cell walls and acts as cement between them
49
What is the water solubility of pectin and its funciton?
It is soluble
Binds adjacent cell walls and holds water in networks.
50
What is the water solubility of gum and its function?
Gum is soluble.
It is a gelatinous exudate from stems or seeds
51
What is the water solubility and funciton of mucilage?
Mucilage is soluble
It is a viscous water holding substance similar to gum
52
What are the structural polysaccharides found in plant cell walls?
1. Cellulose
2. Hemicellulose
3. Pectin
4. Beta glucan
5. Gum
53
What is cellulose?
Linear beta (1,4) linked glucose polymer
Present in all plant materials
54
What is hemicellulose?
* Arabinoxylan
* Polymer of xylose, highly substituted with arabinose plus a small amound of other sugars
* wheat bran, husk and grain endosperm
55
What is pectin as a component of cell walls?
* Galactouronan
* Polymer of galactouronic acids, with varying degree of methylation of the carboxylic acid (methylated galacturonate)
* High level in fruits, low level in vegetable
56
What is Beta glucan?
* Mixed linkage (B 1-3 & B 1-4) glucose polymers
* Oats, barley, wheat grains
57
What is gum as a component of cell walls?
* Galactomannan
* Neutral polymer of mannose, highly substituted with a single
galactose
* Guar gum, locust bean gum, gum Arabic
58
What are the two non cell wall polysaccharides?
Galacto-oligosaccharides
Fructo-oligosaccharides
59
What is galacto-oligosaccharides?
* Oligomer of galactose units build on sucrose backbone
* Widely distributed in plants
* 1-8 % (w/w) in legumes
60
What is fructo-oligosaccharides?
* Oligomer of fructose units
* HIghly soluble
* Example includes inulin
61
Classify the dietary fibres based on whether they are soluble or not
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Classify the soluble fibres as either viscous or non viscous
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Classify the soluble fibres as fermentable or not
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What are the two main roles of polysaccharides in food systems?
1. thickening agents
2. gelling agents
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Which polysaccharides are used as thickening agents?
* Starch
* Modified starch which has alkyl groups conjugated to the starch structure via some of the hydroxy groups
* Gums
* Pectin
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What properties of polysaccharides affect their thickening function?
* Solubility
* Molecular weight
* Water holding capacity
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What do gelling agents do?
They are added to foods to produce gel like consistency
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Which polysaccharides are gelling agents?
Pectin
Alginate
Carrageenan
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How is pectin used as a gelling agent?
* Gelling properties affected by degree of methylation of the galactouronic acids
* Both low and high methoxypectins available, with different gelling property
* Gelling induced by calcium ions
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How is alginate used as a gelling agent?
* From green seaweed
* Highly charged polysaccharide consisting manuronic and guluronic acids
* Gelling induced by calcium
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How is carrageenan used as a gelling agent?
* from brown seaweed
* highly sulfate polysaccharide of galactose
* gel by itself
72
Which properties of polysaccharides affect gelling agents?
* Solubility
* Polymer-polymer interactions
* Electrostatic interaction
* Physical entanglement
* Molecular weight
73
What might be the harmful effects of dietary fibre?
* May displace energy and nutrient dense foods due to bulk
* May interfere with nutrient absorption such as Ca, Fe, Zn due to binding of these minerals
* May cause abdominal discomfort and distention due to excessive fermentation
74
What concerns are raised about lectins?
Issues were raised about the presence of plant lectins in plant based foods due to their perceived harmfull effect to the body
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What are the benefits of a high fibre diet?
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What are the six health effects of a high fibre diet?
1. Reduce calorie intakes
2. prevents constipation
3. Modulate postprandial hyperglycemia (PPH) and insulin response
4. Lower atherosclerosis risk
5. Reduce cardiovascular diseases risk
6. As prebiotics
77
How can a high fibre diet reduce calorie intake?
* Complex carbohydrates provides less fat and added sugar for the same bulk
* Promore weight control by promoting satiety
* solid is more effective in providing satiety compared to liquid dietary supplements
78
How does dietary fibre prevent constipation?
* Lack of bowel movement causes hard stool
* Fibre provides bulk to stool
* More effective if it can interact with water an non fermentable
* Fibre softened stool by retention of water in stool
79
How can dietary fibre modulate postprandial hyperglycemia (PPH) and insulin response?
* Soluble fibre controls the rate of starch/sucrose digestion by control release of starch/sucose from the food matrix
80
How does high fibre diet lower atherosclerosis risk?
* Related to reduction in cholesterol absorption from foods
* Interact with cholesterol prevents it from being dissolved so carried into the colon then its removed and not absorbed
81
How does a high fibre diet reduce cardiovascular disease risk?
Related to reduction in fats and cholesterol absorption from foods
82
How does high fibre diet act as prebiotics?
Promotes beneficial bacterial growth in hind guts (colon)
Sugar released through fermentation which is used by bacteria
