carbohydrates Flashcards
what are carbohydrates made up of
Organic compounds of C, H, & O in the ratio C6H12O6
whats the basic unit of carbs
Basic unit is the sugar molecule or monosaccharide.
how are carbs derived
Derived from photosynthesis: synthesis of CHO from CO2 & H2O in plants in sunlight, with release of O2.
what are the 2 general sources where carbs come from. and name the carbs found from these sources
Plants - starch (storage CHO of plants)
- non-starch polysaccharides
Animals - glycogen (storage CHO of liver &
(skeletal) muscle)
- lactose (milk & dairy products)
- ribose (nucleic acids)
Foods providing CHO are the cheapest source of dietary energy and can provide between 40-80% TEI.
what are the roles of carbs
Sources of metabolic fuels (sometimes the only function in some cells) & energy stores.
Structural components of cell walls in plants & the exoskeleton of arthropods.
Parts of RNA and DNA structure, in which ribose & deoxyribose respectively are linked to purine & pyrimidine bases.
Integral features of many proteins & lipids (creating glycoproteins & glycolipids), especially in cell membranes - essential for cell-cell recognition & molecular targeting.
explain the ‘historical perspective’ of carbs
Main emphasis of CHO as an energy source. (theres not actually a large store of carbs in body)
Thought to be digested in small bowel, and the products absorbed, oxidised in muscle & other tissues and excreted as CO2 & H2O.
“Fibre” thought to pass through gut and be excreted.
- Glucose, galactose , and fructose must be broken down into monosaccharides to be absorbed and in the small intestine. Anything not digested or absorbed in passed to large bowel and so is excreted as waste
explain the digestion and absorption of carbs
Rate & extent to which CHO is digested & absorbed from the small intestine differs.
Some CHO reach large intestine where they are fermented and affect large bowel function.
what are the 3 categories that crabs can be classified into, depending upon monosaccharide bonding)
simple sugars (1-2 mono saccharides) - small
oligosaccharides (3-9) - longer in length
polysaccharides (>9) - large chains
what can simple sugars be classified into
monosaccharides
disaccharides
sugar alcohols
what can oligosaccharides be classified into
malto-oligosaccharides (alpha-glucans)
non alpha-glucans
what can polysaccharides be classified into
starch (alpha-glucans)
non starch polysaccharides (NSP)
explain monosaccharides structure
Consist of 3-7 C atoms, generally in a ring form.
what are monosaccharide sources
Glucose – honey, sugar, confectionery, fruit.
Fructose – honey, fruit & some veg. (mainly fruit)
Galactose – not usually found free in nature. (associated with dairy products)
what are examples of 6 carbon monosaccharides (hexose sugars)
glucose - predominant one , its in table sugar
fructose
galactose
what are examples of 5 carbon monosaccharides (pentose sugars)
ribose
ribulose
explain the physiology of monosaccharides
Absorbed from the small intestine.
Glucose & sucrose give rapid glycaemic responses.
The greater the digestion of food, the longer sugar absorption, giving a slower glycaemic response which is good. Free sugar gives a large glycaemic response which is bad
what does the ringed form in pentose sugars participate in
metabolic reactions
explain disaccharides structure
Polymer of 2 monosaccharides
Formed by condensation between 2 monosaccharides to form a glycoside bond
what are disaccharides sources
Sucrose: cane sugar, fruit, berries, veg
Lactose: milk
Maltose: sprouted wheat, barley
Trehalose: fungi, bread, honey
what 4 groups can disaccharides be split into
sucrose - glu+fru
lactose - glu+gal
maltose - glu + glu
trehalose - glu + glu
explain the physiology of disaccharides
Absorbed
Lactose is fermented in many populations
what does lactase do to glucose
Lactase is specific enzyme that only breaks down glucose
what enzyme do all new born mammalian species have
lactase
describe the breakdown of lactose by enzyme lactase
lactose —-lactase—> glucose + galactose
when does lactase activity rapidly decline
after weaning
when do people generally lose ability to produce lactase
adulthood
explain lactase intolerance
Large amounts of milk lead to unabsorbed lactose which can result in rapid gas production, abdominal pain & diarrhoea.
Occasionally seen in adults of European descent.
Unusual for European people to actually be lactose intolerant
what are sugar alcohols (polyols)
Alcohols of glucose and other sugars.
Found naturally in some fruits and made commercially.
they’re artificial sweeteners. Useful as sweeteners as Poorly absorbed and partly fermented.
what are examples of sugar alcohols
Sorbitol - sucrose replacement for people with diabetes.
Xylitol - has anti-cariogenic action.
lactitol
mannitol
erythritol
explain physiology of sugar alcohols
Poorly absorbed and partly fermented.
what 2 groups can monosaccharides and disaccharides be classified into, and explain them
intrinsic sugars - Naturally incorporated into the cell structure of foods
e.g. eating an apple hole, extrinsic sugars – having a juiced apple. As cellular structure destroyed so sugar is free
extrinsic sugars - Not incorporated into the cell structure of foods
what 2 groups can extrinsic factors be classified into and explain
lactose in milk
- Not a cause of dental caries
- Milk is the only significant source
non-milk extrinsic sugars (NMES)
- Major cause of dental caries
- Advice to cut intake
NMES – eg free sugar
NMES has sugar added or sugar free in product apart from in milk
If add sugar to dairy products like yoghurt its then NMES , but is the sugar is non added and is natural in the dairy then is lactose sugar in the dairy product so doesn’t cause dental carries
what are oligosaccharides
Short-chain carbohydrates.
what 2 groups do oligosaccharides fall into
Fall into 2 groups: maltodextrins and oligosaccharides that are not α-glucans.
what can malto-oligosaccharides (α-glucans) be classified into
maltodextrins
what can other oligosaccharides (non α-glucans) be classified into
inulin
polydextrose
galacto-oligosaccharides
fructo-oligosaccharides
stachyose
raffinose
describe malto-oligosaccharides
Mostly derived from starch.
Include maltotriose, αlpha-limit dextrins
explain sources of malto-oligosaccharides
Widely used in the food industry as sweeteners and fat substitutes.
explain the physiology of malto-oligosaccharides
Digested and absorbed.
explain the structure of the raffinose oligosaccharide
3 monosaccharides: galactose + glucose + fructose
explain the structure of the stachyose oligosaccharide
4 units: galactose + galactose + glucose + fructose
what are the sources of the oligosaccharides Raffinose & verbascose
peas, beans & lentils
what are the sources of the oligosaccharides Inulin & fructo-oligosaccharides
artichokes wheat, rye, onion
describe the physiology of the other oligosaccharides (raffinose and stachyose)
Chemical bonds not susceptible to pancreatic or brush-border enzyme breakdown.
Fermented - some may selectively stimulate growth of bifido-bacteria in large bowel. – so promote large bowel health.
Prebiotics: foods containing oligosaccharides.
they support growth of commensal bacteria.
Probiotics: live micro-organisms added to food e.g. yoghurt.
describe carb fermentation
Some sugars, some starch & all NSP escape digestion & absorption in the Small Intestine and become available as substrates for fermentation by the colonic microflora
what are products of fermentation
CO2
H
CH4
SCFAs - mainly acetate, proprionate & butyrate
explain what happens to the gasses from carb fermentation
absorbed & excreted through lungs or passed as flatus.
explain what happened to the SCFAs from carb fermentation
absorbed by Large Intestine mucosa & may be used as E sources by various tissues.
SCFAs = short chain fatty acids
Fermentation products in particular SCFAs have benefits not just to bowel health but also cardiovascular and metabolic heath
describe polysaccharides structure
Polymers of many 100s of monosaccharide units.
Most important are starch & glycogen (both polymers of glucose).
Other polysaccharides made of other monosaccharides or of glucose units linked differently from linkages in starch & glycogen. These can have mkore structural roles and form a large pprtion of fibre in diet.
Starch and glycogen are energy storing
Glycogen is a highly branching polymer, so isn’t just 1 straight chain
what 2 groups can polysaccharides be subdivided into
non-starch polysaccharides (NSP)
starch (α-glucans)
describe the structure of starch
Long chain glucose molecules arranged in straight or branched chains.
80-90% of all polysaccharide eaten.
Examples:
Amylose (straight)
Amylopectin (branched – 16 bond every 30th glucose)
Modified starches – have branches
provide sources of starch - grains, legumes, and tubers
Grains: wheat, rice, corn, oats, millet, barley
Legumes: peas, beans, lentils
Tubers: potatoes, yams, cassava (starch levels are highest in tubers)
explain the structure of starch
Arranged in granules of different shapes.
Soluble in water when heated – gelatinisation
During cooling – retrogradation (this forms modified starch)
Liquid may be expressed – syneresis = when starch takes on liquid form
what in starch is constantly changing due to its structures
texture and appearance
explain the physiology of starch
Rapidly digestible starch (Very ripe bananas have more digestible starch than under ripe bananas )
Slowly digestible starch – associated with wholegrain cereals
Resistant starch, i.e. resistant to pancreatic enzymes
- Starch physically trapped e.g. whole grains, seeds
- Resistant granules e.g. raw banana
- Retrograded e.g. potato salad
- Chemically modified to resist digestion
Very ripe bananas have more digestible starch than under ripe bananas
why might manufacturers modify starch
to give a more branched molecule and change its properties
what properties can modified starch act as in products made by manufacturers
Thickening agent
Stabilizer
Emulsifier
what starches are used in manufacture starch modification
Arrowroot
Cornstarch
Potato starch
Sago
Tapioca
what is glycogen
The storage form of carbohydrate in animals found in muscle and liver.
in muscle glycogen provides an extra source of what
a source of extra glucose for strenuous activity.
how is there little to no carbs in meat
because Tissue enzymes break glycogen down once animal slaughtered
how many grams of glycogen are in human body
Only 200-500g of glycogen in human body unless carbohydrate loading by athletes.
why do athletes need more glycogen
More glycogen in athletes muscles the longer they can contract for
what stores glycogen
Liver stores glycogen to maintain blood glucose levels in the face of a fast
Livers glucose store is not a large store
what are non starch polysaccharides (NSPs)
Polysaccharides that cannot be digested by normal enzymes of the human gut.
Non alpha-glucans
NOT to be used interchangeably with fibre
it is fermented
what are examples of NSPs
cellulose, hemicelluloses, inulin, chitin, pectin, gums and mucilages
Chitin is carb that forms hard exoskeleton in shell fish.
Small shrimps that you don’t de shell, provide you with chitin in diet
what source of food type does most fibre come from
plant sources
what is the structure of cellulose
Straight chain of glucose residues connected in a beta 1-4 linkage
what structure in plants is cellulose found in
cell wall
if the Bond of oxygen is below plain of chairs what type of linkage is it
alpha linkage
if the bond is sitting above the plain of the chairs what type of linkage is it
beta linkage
name the other types of NSP
hemicellulose
inulin
chittin
pectin
describe hemicelluloses
what they include and what theyre composed of
Include xylan, glucuronoxylan, arabinoxylan, glucomannan, and xyloglucan.
Composed of various monosaccharides (e.g. xylose, mannose, galactose, rhamnose and arabinose) with many branching side chains
Hemicellulose Have glucose backbone with branching side chains that vary depending on what monosaccharides they contain
what are hemicelluloses found in
Found in outer bran layer of many cereal grains, legumes, veg & nuts.
If food has hard outer coating then the outer coating will be composed of hemicellulose. However often this outer coating is peeled off for ex in veg
what is inulin, in terms of structure
Collection of fructose polymers of different lengths
what is inulin found in
Found in wheat, onion, garlic, bananas & asparagus
explain the structure of chittin
Long chain polymer of Nitrogen-acetylglucosamine
what sources is chittin found in
In exoskeletons (e.g. crabs & lobsters) and cell walls of most fungi.
Chitin isn’t found in static shell fish like muscles and oysters
Chitins also found in prawns
Some insects also contain chitin
describe pectin’s structure
Main component is units of galacturonic acid
what are sources of pectin
fruits
what is the property of pectin
its gel forming
what is the function of gums and mucilages
Thick gel-forming fibres that hold plant cells together
what are examples of gums
seaweeds (carrageenan)
trees (gum Arabic) – tree sap
bacterial fermentation (xanthan gum)
what is an example of mucilages and explain their function
psyllium or ispaghula – of the Plantago ovata plant
this helps with constipation as is a fibre
what are the consequences of low NSP diets
Small volumes of bowel contents which move slowly & allow harmful residues to persist.
Linked with:
Haemorrhoids
Diverticular disease - forms pouches in wall
Colon cancer-
Colon cancer- to bowel wall with toxic material
