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Nutrition Semester 2 > BMS1064 - Carbohydrates > Flashcards

BMS1064 - Carbohydrates Flashcards

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1
Q

The guidelines suggest that the total carbohydrate should provide for __% of total dietary energy.

Free sugars should not exceed __% and gibre should be ___g/day.

A

47%
5%
30g/day

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2
Q

What could too much and little CHO intake lead to?

A

Too much: levels >75% of total energy intake have adverse effects (exclusion of protein, fat and other essential nutrients from the diet), tooth decay.

Too little: protein diverted from essential functions, CHO needed to metabolise fats, unusual products of fat breakdown (ketones) accumulate (ketosis

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3
Q

What are the functions of carbodhyrates?

A

1) Important energy and C source
2) Store energy
3) Flavouring -> react to form flavours/colours (Maillard reaction, caramelisation etc)
4) Functional incredients
- sucrose allows ice cream to be soft
- gums
- prebiotics - feed bacteria
- fat replacers

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4
Q

What is the difference between oligo- and polysaccharides?

A

Oligosaccharides = 3 to 10 monosaccharides covalently linked

Polysaccharides = >10 monosaccharides covalently linked

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5
Q

What is the formula for CHOs?

A

Cn(H2O)n

from carbon and water

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6
Q

CHOs are polyalcohols (C-OH). What groups do polyalcohols have?

How many carbons do the simplist sugars have? What are they structural isomers of?

A

Aldehyde or ketone groups

3 carbon atoms (trioses)
C3H6O3

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7
Q

What are the simplist members of aldehydes and ketones containing sugars called?

A

Aldoses and Ketoses

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8
Q

When is an object or molecule chiral? When is a carbon atom chiral?

A

If it cannot be superimposed

A carbon atom is chiral if it has 4 different groups attached. Thus they form 2 steroisomers.

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9
Q

What are steroisomers?

A

Molecules with the same molecular
formula and general structure, but with different configurations at each chiral atom

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10
Q

How do we count the number of C atoms in a sugar?

A

From the end closes to the carbonyl group

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11
Q

For a molecule with 3 chiral centres. How many steroistomers does it form?

A

2^3 = 8

2^number of chircal centres = no. of steroisomers

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12
Q

What are enantiomers?

A

Compounds related by inverting configuration at ALL chiral carbons .

Molecules that have the same molecular formula and connectivity of atoms but differ in their spatial arrangement, making them mirror-image isomers of each other.

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13
Q

What are diastereomers?

A

Compounds related by inverting configuration at ONE OR MORE, but not all chiral centres (not mirror images).

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14
Q

What are epimers?

A

Diastereomers with an inverted configuration at JUST ONE chiral carbon

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15
Q

All Epimers are ____1_____. But ____1____ are not epimers. Enantimomers are not ____1____. All of these are ____2____.

A

1 = diastereomers
2 = steroisomers

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16
Q

Cyclisation of glucose produces a new asymmetric centre at C-1, with the two new steroisomers called ________. These come in two forms called ____ and ____. These forms are interchangable via _________ (switching back and forth between ring and straight-chain form).

A

anomers

alpha and beta

mutarotation

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17
Q

What is the only common ketose?

A

Fructose - also the sweetest natural sugar.

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18
Q

What sugar is rare in foods in free from?

A

Galactose - found in milk products after lactose hydrolysis.

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19
Q

Whats the commonest pentose? Where is it found?

A

Ribose - found in meat, fish and poultry (flavour precursor)

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20
Q

What is the difference between furanose and pyranose forms?

A

Furanose - 5 membered ring
Pyranose - 6 membered ring

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21
Q

What is the structural difference between glucose, fructose, galactose and ribose? (two alpha, two beta / two furanoses, two pyranoses)

A

Ribose - alpha form
5 membered ring (furanose)

Glucose - alpa form
6 membered ring (pyranose)

Fructose - beta form
5 membered ring (furanose)

Galactose - beta form
6 membered ring (pyranose)

[All are CH2OH]

Glucose and fructose in image

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22
Q

Why is the structure of fructose complicated? [not needed to know]

A

Can form furanose and pyranose rings. Can have alpha or beta conformation.

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23
Q

Why is maltose (a-glucose+b-glucose) a reducing sugar?

A

Because it has a free anomeric carbon (a carbon bonded to 2 oxygen atoms, one of which is an -OH group (C-1) ) - and so can be oxidized.

Reducing sugars can be oxidized.

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24
Q

what is the difference between L and D glucose?

A
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25
What is the name of the first sugar? What about the second?
First recognise its D-glucose Then its form - furan/pyran/ring 1. a-D-glucopyranosyl 2. (1-->4)-D-glucopyranose
26
Give the full name of this sucrose molecule
a-D-glucopyranosyl 1-->2 linkage B-D-fructofuranose = a-Dglucopryanosyl-(1-->2)-B-D-fructofuranose
27
Is lactose a reducing sugar?
Yes because it has a free anomerica carbon on glucose (C-1).
28
Is Trehalose a reducing sugar? In what animals does it serve as an energy storage compound? What contains 10-25% trehalose by dry weight?
No. No anomeric carbon. In insects mushrooms
29
What does Trehalose protect organisms against? Why is it good in cosmetics? How is it used in pharmaceuticals? How can genetic modification be used?
protects against stresses - e.g. drying/freezing/salt stress. --> 'resurrection plant' has moisture-retaining capacity - used as a moisturizer in many toiletries Preserves tissues and protein, used in organ transplant protection solutions etc GM: cloning genes can generate drought resistant varieties
30
Different linkages result in the formation of different disaccharides. What are the the examples from glucose?
31
What does the term 'sugar' refer to? What about 'sugars'? 'Free sugars'?
Sugar = sucrose only Sugars = mono- and disaccharides only Free sugars = white/brown sugar, honey, High Fructose Corn Syrup, coconut sugar, syrups, fruit/veg juices, glucose/dextrose etc NOT natural dairy and fruit/veg sugars.
32
What is the difference between where we get Sugar Beet and Sugar cane from?
Sugar beet - UK grown and processed Sept-March Sugar cane - tropical/process (shipped raw). Throughout year. 1 UK refinery.
33
What are the uses of sucrose?
Sweetener, flavour and colour precursor, fermentation substrate, biodiesel
34
What happens when you heat sucrose? What is the sweetness standard for sugar? Honey: plant supplied ______ (nectar), bees secrete invertase (--> ______/_______): bee vomit
Inversion: Sucrose--> glucose + fructose Sucrose is the sweetness standard for sugar -> 1 or 100. Other sugars are compared to this. sucrose fructose/glucose
35
During brewing processes barley amylases convert starch into ______. The metabolism of this disaccharide by yeast during fermentation leads to the production of ______ and _____ ______.
maltose ethanol and carbon dioxide
36
How are sugar alcohols produced? Do they have more or less calories?
By the hydrogenation of sugars and syrups Fewer calories
37
What are the benefits of sugar alcohols? What are some issues?
+ Cause only a very small rise in blood glucose and insulin levels. +Non-cariogenic (do not cause tooth decay) + Xylitol and sorbitol impart cooling sensations/ - Need to be labelled as having a possible laxative effect - Are FODMAPS, which may be an issues for those with IBD
38
Where are oligosaccharides found? Give an example. What is their sweetness like? Are they soluble? Digestible by human enzymes? What does FODMAP stand for?
Found in artichokes, chircory etc e.g. FOS (fructooligosaccharide) Some sweetness Soluble Not digestable by human enzymes. May act as prebiotics. FODMAP -> Fermentable Oligosaccharides, Disacccharides, Monosaccharides and Polyols
39
What does FODMAP stand for?
FODMAP -> Fermentable Oligosaccharides, Disacccharides, Monosaccharides and Polyols
40
What are the categories of polysaccharides?
Homopolysaccharides - single type of monosaccharide - e.g. starch, glycogen and cellulose Heteropolysaccharides - contain 2 or more different monosaccharides - e.g. alginate and gelllan gum
41
Describe the structure of cellulose at different scales
Cellulose chains held together by H-bonds 18 chains make up each cellulose microfibril Layers of microfibrils in plant cell wall make it strong. Main source of dietary fibre.
42
Name 3 other polysaccharides in food and there uses.
Alginate (brown seaweed) - thickner/gelling agent Arabinoxylan (bread) - moisture retention B-glucan (oats and barley) - binds to help reduce cholesterol.
43
__________ comes from konjac (asian root vegetable). It is a soluble polymer of glucose and _______, with _________ substituents. used in low-calories shiriaki noodles. Also an _______/thickener. __________ is found in all fruit and vegetable cell walls. It has a glucose polymer backbone with xylose substituents.
Glycomannan mannose galactose elmulsifier Xyloglucan
44
What are examples of dietary fibre?
Non-starch polysaccharides (NSP): - cellulose (insoluble) - hemicellulose, pectin (partially soluble) - stabilizers, thickeners, gelling agents (soluble) Resistant starch Oligosaccharides
45
What is resistant starch?
A form of polysaccharides that are not digestible. Acts as a prebiotic. Foods high in resistant starch include cooked and cooled rice, green bananas, raw oats, and various legumes.
46
Compare amylose and amylopectin.
Amylose - unbranched chains of D-glucose connected by 1-4 linkages. Amylose - same as amylose but branched with 1-6 linkages
47
What must happen to starch for it to gelatinise? What does this lead to?
It must be heated in excess water. leads to irreversible change in the ordered structure of the starch granule: - water uptake, granule swelling - loss of birefringence - crystallite melting -unwinding of double helices - amylose leaching - starch solubilisation increased viscosity - gelling of amylose on cooling
48
What is retrogradation?
Occurs as starch cools to form a gel network form the leached amylose chains. Continues during freezing. New structures formed are not the same as the native starch granules. Texture of gel controlled by ratio of amylose: amylopectin.
49
What is Dextrinisation?
A process where the starch in food breaks down into smaller molecules called dextrins when subjected to dry heat, resulting in a brown color and a crispier texture
50
The Cook’s Perspective * Flour added to hot fat and cooked off (the roux) * Liquid added gradually * Heated gently until thickened * Left to cool it will get thicker * Overcooked roux has less thickening power What is the scientist's perspective?
* Heating the flour with fat coats the starch granules, keeping them separate * The swelling of starch is gradual (smoother sauce) * Boiling will disintegrate the granules * Retrogradation (on cooling) allows amylose to assemble into a network * Dextrinisation shortens chains, gives thinner sauc
51
What happens to starch granules in boiled mashed potato? How does this give it's texture? What happens if you overmix it?
Granules swell, only some burst. Bulging cells separate to give floury texture. Overmixing -> makes glue. Cells burst, releases starch, slimy paste.
52
Why does pasta not expand too much in water when boiled? (think starch granules)
Granules trapped in a solid (less water access). Proteins compete with starch for limited water. Limited expansion of granule.
53
What happens to the starch granules in chips/roast potatoes?
* At high temp water evaporates and fat enters * Dextrinisation forms crust, colour, texture, flavour * Starch granules do not swell so much to break open cells, due to lack of water- floury texture
54
Name some unprocessed functional starches.
Waxy maize - granular integrity maintained under mixing Rice - soft, creamy smooth Tapioca - clear solutions Hylon - resistant to digestion
55
How is pregelatinized starch made? How does this affect its properties?
Preheated with water to gelatinise and rapidly dried to make powder. Weaker gel, less viscous paste and instant. e.g. used in instant soup
56
MODIFIED STARTCHES How is thin boiled/acid modified/depolymerised starch used?
Hydrolysis of few glyosidic bonds. Increase solubility and clarity. used in gummy sweets
57
MODIFIED STARCHES How are stabilised starch phosphates and starch esters used?
Freeze-thaw resistant gels Phosphate stabilised - high paste viscosity Succinate stabilised - emulsifier
58
How does cross-linked starch affect food? (25% of all starches in food are cross-linked)
Strengthens granule structure. Resistant to pH and mixing (shear) Slow to gelatinise. e.g. in canned fruit pie fillings
59
What are the rules with modified starches?
Must be described as such on the label. Some are considered to be additives (have an E number)
60
Measuring the reactivity of common food hexoses: Aldehydes are easily oxidised to _________ _____. This reduces _____ to Cu+ (Fehling's Test), changing the colour from blue to _____. This shows that glucose is a ________ sugar.
carboxylic acid Cu2+ red reducing
61
Reducing sugars undergo the _________ reaction in the presence of _____ ______ and produce colour and _______compounds. Ketones are not easily _______. So fructose, shoud be a __________ sugar. However, under the conditions of the test, it can rearrange itself to have an _______ group, so that fructose can be _________ and therefore it is a ________ sugar too (for this test).
Maillard reaction amino acids flavour compounds oxidised non-reducing aldehyde group oxidised reducing
62
name the reducing and non-reducing sugars
63
MAILLARD REACTION What happens when you heat a reducing sugar with an amino acid? Whats the difference in the reaction with glucose and reaction with glyceraldehyde (with glycine)? How does acid affect the rate of reaction?
Colours and flavours and some carcinogens produced Glucose+glycine - slower reaction as glucose in ring form Glyceraldehyde + glycine - faster reaction as no ring form. Acid slows it down by protonating the amine.
64
Monosaccharides form _______ bonds with water - so are very ________. The __________ of sugars will affect how energetically favourable this process is. Pectin sometimes hydrates _____ on outer surface making it diffficult for water to access the inside of the particle. Cellulose hydrogen bonds with ____. Starch is only a true solution at low __________ above the gelitinisation temperature, but can add ____ _____ and get pastes.
hydrogen hydrophilic - so soluble configuration quickly itself concentration more starch
65
Practical: Starch-Iodine binding Amylose chains form ______. Iodine solution contains elemental iodine and _________ _______. This dissociates to give __ and I3-. I3- fits into the centre of the ______ Colour changes from orange/brown to ____/_____. Confirms the presence of amylose.
helices potassium iodide K+ helix blue/black
66
Enzymatic methods to measure CHO content: a-amylase breaks ______ glucose bonds only. Lichenase breaks ____ glucose bonds only. What do you need to standardise?
alpha 1-4 beta 1-4 * Enzyme concentration * Substrate concentration * Time * pH * Temperature
67
When testing the % of starch digested by enzymes. What are the advantages to measuring the extent of product accumulation and substrate loss and initial rate of reaction?
Its rapid. High specificity Sensitive to low concs of CHO Many enzyme kits available commerically
68
What are some examples of enzymes used to measuring CHO content of food?
Glucose oxidase and Peroxidase Produce precipitate Record absorbance at 510nm
69
What are 2 physical methods to measure CHO conc.
Polarimetry and Refractive Index
70
A chemical method of assessing and expressing the nutritional value of food: What is the equation to calculate carbohydrate %?
100- (% moisture + % lipid + % protein + % mineral)
71
Stachyose and Raffinose CHOs - are they digestible? What kind of molecules are they?
Indigetible oiligosaccharides
72
Glucose is taken up into cells via which molecule?
SGLT1 - Sodium Glucose Linked Transporter 1 driven by low intercellular sodium (gradient). Glucose moved with sodium. Na+/K+ pump keeps Na+ levels in cell low.
73
How does fructose move into cells?
Via GLUT 5 protein by facilitative diffusion. Down conc cradient.
74
How does fructose and glucose leave the cell?
Via GLUT 2 protein.
75
What is the GI of glucose?
100
76
How does muscle mass affect glucose uptake?
more muscle mass --> increased n.o. of glucose receptors - take up glucose faster.
77
What affects GI? What does not count towards GI?
Cooking, processing, ripeness, meal composition, time of day. Fructose
78
What is the equation for glycaemic load? What is the difference between GL and GI?
Amount of CHO x GI / 100 GL takes into consideration the portion size of CHO.
79
Does fibre contribute to GI?
No - no effect on blood glucose Gut bacteria release glucose from fibre but it doesn’t get into our bloodstream.
80
How does soluble and insoluble fibre compare?
81
What is crude fibre?
'crude fibre' - residue of plant foods left afer extraction by dilute acid and alkali. Way of measuring dietary fibre.
82
Are DRVs for sugar and fibre being met by UK population?
No. Defo not. Around half the recommedned intake.

Nutrition Semester 2 (23 decks)

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