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Carbohydrates

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Title: Carbohydrates


1
Carbohydrates
  • Anna Drew
  • with grateful acknowledgement for inspirational
    teaching received at
  • The School of Pharmacy, University of London

2
  • Uses
  • green plants
  • store energy as CHO
  • eg starch
  • structural material (form large proportion of
    plant biomass)
  • eg cellulose
  • Structures
  • mono 1 unit
  • di 2 units (useful in pharmacy)
  • oligo 2-8 units
  • poly N units

3
  • Type sugar varies enormously
  • Formation
  • sugars are formed as a result of photosynthesis
  • glucose-6-phosphate and fructose-6-phosphate
  • hydrolysed to glucose or fructose and converted
    to starch or consumed as energy
  • form sugar nucleotides with UTP or ATP -gt uridine
    diphosphoglucose etc and converted to different
    sugars
  • sugars unite with a wide variety of compounds to
    form glycosides

4
Monosaccharides
  • 3-9 carbon atom sugars
  • (pentoses 5, hexoses 6 most common in plants)
  • have to be obtained by chemical reactions
  • only a few are free in plant
  • many as polysaccharides
  • A Dextrose (glucose)
  • dextrose-a-D-glucopyranose (pyranose form)
  • produced by hydrolysis of starch-HCl under heat
    pressure (45lb per sq in for 30min)
  • dont want a mixture eg with maltose in

5
  • Uses
  • nutrient replenishment PO or IV
  • dextrose injection
  • dextrose saline (NaCl) injection
  • dextrose sodium citrate injection
  • other forms
  • B Glucuronic acid
  • 6C Ch2OH -gt acid (glucuronic or gluconic)
  • from oxidation of glucose
  • Uses
  • as calcium or ferrous salts
  • calcium glucuronate for osteoporosis (loss of
    calcium from skeleton etc)
  • ferrous gluconate for anaemias (gluconate form
    less irritant to GI tract and better absorbed
    than other salts)

6
  • C Liquid glucose
  • Mixture of dextrose, maltose or dextrins
  • from incomplete hydrolysis of starch
  • (less pressure 30lb per sq in)
  • Uses
  • as sweetners, substitutes for sucrose in syrups
  • D Fructose
  • Occurs in fruits
  • obtained from hydrolysis of sucrose
  • Uses
  • as sweetner in diabetic foods instead of glucose
    (not a problem since it is not easily metabolised)

7
Disaccharides
  • Condensation of 2 monosaccharide molecules
  • Two main ones
  • 1 Sucrose
  • a-D-glycopyranosyl-ß-D-fructofuranose
  • glucose fructose
  • Main sources
  • Sugar cane Saccharum officinarium
  • crushed, boiled in lime, coagulated protein
    removed by filtration, decolourised, then
    crystallised (remainder in cattle food)
  • Used as a sweetening agent

8
  • Sugar beet Beta vulgaris
  • sliced and boiled in hot water, then as above
  • Uses
  • cherry/raspberry juice as a masker
  • esters many OH and ethanolic groups can be
    added to form esters easily used as emulsifiers
    and wetting agents or dispersants, lotions, gels
    non-irritant so can be used internally
  • 2 Lactose
  • galactose glucose
  • Source
  • does occur in plants but normally obtained from
    cows milk (commercial by-product of cheese)
  • Used as
  • tablet diluent esp in antibiotic preparations
  • nutrient in infant foods

9
Polyols
  • Sugar alcohols
  • occur naturally
  • produced from reduction of unit sugars
  • (removal of aldehyde or keto group)
  • Sorbitol (D-glucitol)
  • From sorbose in
  • Sorbus aucuparia (mountain ash red berries)
  • many rosaceous fruits
  • seaweeds
  • Mannitol
  • From mannose in
  • Travinus ornus (damaged stems)
  • seaweeds (main commerical source)

10
  • Uses
  • both used as alcohols
  • less sticky to deal with in biochemistry
  • Mannitol
  • limited uses
  • diagnostic reagent in kidney tests
  • not metabolised
  • diluent
  • diabetic foods
  • Not as sweet as sucrose or glucose
  • Sorbitol
  • diabetic foods
  • with sucrose to stop crystallisation of sucrose
  • eg in toothpastes, cosmetic creams

11
Polysaccharides
  • Condensation of sugar phosphates and sugar
    nucleotides
  • Polyuridines (acid sugars) occur in polymers
  • Building blocks
  • Hexoses
  • D-glucose, D-mannose, D-fructose, D-galactose
  • Pentoses
  • D-xylose, L-arabinose
  • Modified sugars
  • D-glucosamine, D-glucuronic acid, D-galacturonic
    acid. D-mannuronic acid, L-fructose, L-rhamnose

12
  • Starch essentially a storage form of sugars a
    1-4 links
  • Cellulose building material of the plant ß 1-4
    links
  • glycosidic bonds initiated at the C1 anomeric
    centre
  • sugars and polysaccharides normally an orderly
    arrangement of two components
  • not all are straight chain polymers

13
STARCH
  • Amylose mol wt 103104
  • Amylopectin mol wt 107
  • formed in leaves
  • can be reconverted to translocating form
    (transitional starch) to go to other parts of
    the plant

14
  • Source
  • found mainly in seeds, fruit, tubers
  • exception is the stem of the sago palm
  • good commercial sources
  • potato, maize, wheat, rice, oat, barley
  • tapioca or cassava in tropics
  • arrowroot, banana, buckwheat, sago palm stem
  • Amylose
  • unstable H-bonding between molecules hydrolyses
    in dilute solution
  • easily precipitated can never get it back
  • Amylopectin
  • major constituent of starch
  • forms very viscous solutions
  • stable in water, good in pastes
  • use of amylose or amylopectin depends on
    requirements
  • if want greater amylose choose certain hybrids

15
Evans WC. Trease Evans Pharmacognosy. 14th
Edition. London WB Saunders, 1996
16
(No Transcript)
17
Starch hydrolysis
  • i) phosphorylase
  • found in plants
  • hydrolyses amylose -gt glucose-I-phosphase
  • which attacks outer chains of amylopectin
  • cant reach or breakdown a1,6 links in molecule
  • ii) amylase
  • hydrolyses straight chains links but not a1,6
  • amylose -gt glucose maltose multitriose
    molecules
  • can work on ß-amylose
  • iii) a-glucosidases
  • a1,4 links hydrolysed not a1,6
  • commerical fungal enzymes needed to hydrolyse
    a1,6 linkages

18
Commercial preparation of starch
  • Sources maize, rice, potato
  • MAIZE (Zea mays)
  • starch is found in the endosperm
  • embryos also useful

Pericarp testa
Embryo (germ)
Endosperm (grain)
19
  • soak in water 0.2 sulphurous acid (SO2) at
    50oC for 2 days to remove pericarp (testa)
  • roll to split, partially crush and separate
    embryo endosperm
  • embryo contains oil so floats and is skimmed off
  • wash endosperm with water
  • liquor passed over series of shaking-sieves,
    concentrated by sedimentation and deposited over
    tables with troughs tabling
  • each repetition reduces protein level
  • Nowadays repeated centrifugation used to
    collect starch sediment
  • undergoes drying process
  • Embryos
  • pressed to yield maize oil
  • contains vitamin E
  • germ seed cake fed to cattle

20
  • RICE (Oryza sativa)
  • grains softened by soaking in 0.5 caustic soda
    (NaOH)
  • loosens and partially dissolves glutinous matter
    holding starch granules together
  • ground in stone mill -gt milky fluid (starch
    suspension)
  • diluted and allowed to settle in vats ie
    concentrated by sedimentation
  • drained over cloth lined boxes
  • (or centrifuged to remove starch)
  • undergoes drying process

21
  • POTATO (Solanum tuberosum)
  • contain 16-25 starch
  • easier to separate it than via cereals
  • skin removed
  • contains enzymes that discolour starch
  • rasped to a pulp in teeth-lined drums
  • tears open most cells
  • starch separated by shaking-sieves, residue
    ground between millstones, repeat
  • liquid centrifuged
  • concentrated starch mixed with water and further
    purified by sedimentation in vats
  • dried to reduce lt20 moisture

22
Uses
  • 1 Starch - absorbent properties
  • dusting powder
  • ointments (mucilage of starch)
  • disintegrating agent in tableting
  • 2 Other starch products
  • starch doesnt dissolve in cold water
  • isnt readily adsorbed
  • hence it is slightly altered

23
  • i) Formalised starch
  • treated with formaldehyde
  • removes swelling properties in water
  • can be adsorbed by body - used in surgeons gloves
    (can be sterilised)
  • Uses - lubricant properties many uses in food
    industry (gels, pastes)
  • ii) Soluble starch
  • (a) from potato
  • mixed with ethanol and acid at 10mmHg
  • neutralised with NaCO3
  • washed with ethanol
  • grains still look same
  • in cool water get an opaque solution
  • (b) from maize
  • same treatment
  • or put through rollers to get same effect
  • or use chlorination process to get a gel form
  • Used in tableting as soluble

24
  • 3 Commercial dextrins and dextrans
  • a) Dextrins
  • prepared by acid and heat -gt white dextrin
  • or just heat (roasting starch) -gt yellow dextrin
  • white has less adhesive properties
  • smaller molecule since partly broken down by acid
  • Main use
  • adhesive dressings
  • food products (binding pastes, thickeners)
  • b) Dextrans
  • not starch
  • polymer of 1,6 links of glucose units
  • formed by many microorganisms
  • commercially used Leuconostic mesenteroides
    converts sucrose -gt a 1,6 glucose dextrans
  • Used
  • as blood plasma expanders (severe haemorrhage,
    bad burns)

25
  • INULIN
  • fructose polymer
  • stored in some plants as an alternative food
    reserve to starch
  • chicory (Cichorium intybus)
  • dandelion (Taraxacum officinale)
  • mammalian enzymes cant break it down
  • readily excreted in urine
  • Used
  • to determine GFR (glomerular filtration rate)
  • sweetening agent

26
CELLULOSE
  • Cell walls
  • cellulose pectin hemicellulose derived sugar
    molecules ( lignin -gt 2y thickening)
  • pectin most useful

Proposed model of a primary plant cell wall
27
  • Cellulose straight chain glucose polymer
  • has ß 1,4 links (1,4-ß-D-glucopyranosyl units)
    but cannot form a helix
  • gt different properties with strength
  • used as building block rather than energy store
  • large part of molecule cellulose
  • fibres parallel held by H-bonds and Van der Waals
    forces
  • some parts of molecule are crystalised
  • amorphous regions of molecule hydrolysed more
    easily

28
Commercial preparation
  • Source cotton
  • 98 cellulose
  • remove impurities, pectin proteins
  • de-wax with solvents
  • boiled in O2 free alkali to get pure cellulose
  • microorganisms or strong acid heat needed to
    break down cellulose
  • cellulose -gt cellobiose (dimer) -gt glucose

I cellobiase
I cellulase
29
Uses
  • Dressings
  • good absorption
  • wont dissolve in most solvents
  • some swelling with moisture
  • dissolved with freshly prepared CuOxam
  • Filtration and chromatological medium
  • Tableting
  • partially hydrolyse microfibrils to get certain
    properties
  • or use a little or in combination
  • makes tablets hard but can be used in tablet
    coating

30
Cellulose derivatives
  • -OH groups replaced
  • Cellulose acetate
  • acetate replaces approx 2.3-3 OH groups per
    molecule
  • 25 cellulose acetate 75 cellulose phthalate
    combination used for tablet coatings
  • Methylcellulose
  • product produces viscous suspensions
  • good emulsifier
  • Vegetable and mineral oils, barrier creams, bulk
    laxatives, tablet binder

31
  • Hydroxycellulose
  • Carboxycellulose
  • used as thickeners and stabilisers for pceutical
    and dairy products (viscous solutions)
  • also creams and tablet coatings sometimes
  • Oxidised cellulose
  • 20 -OH groups converted using HNO2 acid
  • haemostatic properties
  • gauze linen dressings, in lint
  • Cellulose nitrate
  • nitration of polymer - guncotton
  • collodion (solution produced by dissolving in
    ether or organic solvents) used as skin coatings
    over abrasions (wound dressing, topical med.
    carrier)

32
PECTIN
  • Mol wt 104-105
  • hydroxy groups oxidized then methylated
  • from galactose
  • methylation not always complete
  • Useful high mol wt polymer
  • tends to coagulate with Cu and Al ions in aqueous
    -gt viscous solutions, gels
  • diarrhoea preparations eg kaopectate
  • haemostatic substitute for plasma therapy in
    shock
  • Source best from fruit eg apple, pear

33
GUMS
  • Mixtures of following give different physical
    properties
  • galactose, mannose, xylose, arabinose, rhamnose,
    fucose (an aldose/hexose deoxy sugar C6H12O5)
  • 3 types
  • exudate gums
  • seed gums
  • seaweed gums

34
  • A Exudate gums
  • 1 Acacia
  • From Acacia senegal (Leguminosae)
  • grows in Sudan, Central and West Africa
  • trees grow in semi-arid conditions
  • produce gummy exudate to repair damage
  • by animal, insect or man
  • when 6 years old
  • tapped to collect acacia gum
  • comes in round balls tiers
  • sorted by size and colour
  • darker if phenol present
  • should be clear or glassy

35
(No Transcript)
36
  • has no odour or taste in aqueous solution
  • 1-6, 1-3 links containing L-arabinose, L-rhamnose
    and mainly D-galactose D-glucose (glucuronic
    acid)
  • galactose 3 arabinose 3 glucuronic acid 1
    rhamnose 1
  • soluble in water, makes low viscosity solutions
  • easily digested and absorbed
  • non-toxic
  • Uses
  • stabiliser in emulsions
  • cough, diarrhoea, throat preparations (demulcent
    properties)
  • expensive but the best

37
  • 2 Tragacanth
  • From Astragalus gummifer and other species
    (Leguminosae)
  • thorny shrub growing at 1000-3000m
  • in Anatolia, Syria, Iraq, Iran, former USSR
  • produced immediately from pith and cortex
    breakdown in damaged bark
  • stringy, contains starch

38
  • polymer more acidic than acacia
  • main acid is D-galacturonic acid (43)
  • Constituents
  • tragacanthin (acid groups, water-soluble) 1
  • bassorin (no acid groups, water-insoluble
    fraction) 2
  • both insoluble in alcohol
  • best grades contain least tragacanthin
  • but where it is at a high level found to contain
  • galacturonic acid (43), xylose (40), L-fucose
    (10), D-galactose (4)
  • separated by precipitation less easily than
    acacia
  • forms a translucent solution since insoluble
  • Uses suspending agent, thickening agent,
    tableting

39
  • 3 Sterculia
  • From Sterculia urens
  • Karaya gum, Indian/Bassora tragacanth
  • India, Pakistan, Africa
  • previously thought an inferior substitute for
    tragacanth
  • similar but D-galacturonic acid linked to
    rhamnose
  • contains no starch (stains pink w ruthenium red)
  • Uses
  • granular grade bulk laxative
  • powdered grade lozenges, pastes, denture
    fixative powders, stoma adhesive

40
  • B Seed gums
  • 1 Psyllium seed (flea seed)
  • From
  • Plantago afra, P.indica French/Spanish psyllium
  • P.ovata blonde psyllium, ispaghula, Indian
    plantage seed
  • epidermis of the testa
  • Neutral polymer (mucilage) from the seed coat
  • ground to produce powder
  • not purified
  • D-galacturonic acid L-arabinose, D-xylose and
    L-rhamnose
  • Uses
  • demulcent
  • chronic constipation (ispaghula husk SF 40-90)

41
  • 2 Locust bean, carob gum
  • From Ceratonia siliqua (Leguminosae)
  • endosperm separated from seeds
  • Cyprus, Egypt, Mediterranean
  • Major units mannose and galactose
  • branches shorter and less branched gives
    advantages
  • neutral
  • Uses
  • as for tragacanth
  • food industry thickener in place of starch
  • not such a good suspending agent (contains an
    enzyme)

42
  • 3 Guar gum
  • From Cyamopsis tetragonobulus
  • ground endosperms
  • Indian leguminous plant
  • Main constituent galactomannan
  • Uses
  • food industry 5-6x thickening power of starch
  • ? oral hypoglycaemic drug changes in gastric
    emptying and GI transit time
  • lowers cholesterol levels - ? binding bile salts
    in gut

43
  • C Seaweed gums
  • major components of cell walls
  • can be extracted from
  • red algae - Rhodophyceae
  • brown algae - Phaeophyceae
  • with boiling water
  • 1 Alginic acid
  • From brown seaweed
  • Macrocystis sp., Laminaria sp.
  • grows in colder waters of the world
  • N.Atlantic Ascophyllum nodosum cut with sickles
    or harvesters, rest storm-cast
  • processed or dried to 12-17 moisture for storage

44
  • Extraction Stanford method
  • dried milled weed macerated with dilute Na
    Carbonate solution and mass diluted with soft
    water
  • insoluble matter decanted or settled out
  • clear liquor
  • poured into dilute sulphuric acid or dilute Ca
    Cl2 solution
  • insoluble alginic acid or calcium alginate
    precipitate out
  • rolled to expel remaining liquid
  • OR ethyl alcohol added to precipitate out sodium
    alginate
  • D-mannuronic acid L-guluronic acid (20-40)
  • in blocks of alternating units and blocks of
    single units
  • quite highly acidic straight chain polymer (MW
    50-200,000)
  • contains trapped ion salts eg Ca2 in guluronic
    acid kinks (egg box gel)
  • Uses -gt viscous solutions, no taste or toxicity,
    many uses!
  • food, dental, rubber, textile, paint, cosmetic,
    pceutical indy
  • suspending, thickening, stabilising, gelling with
    salts etc
  • pceutical barrier creams, ointments, pastes,
    jellies, tablets, gastro-oesophageal reflux
    products
  • textile wound dressings (haemostatic)

45
  • 2 Agar
  • From red algae
  • Gelidium sp., Gracilaria sp.
  • Extraction Japanese coast
  • cultivated by placing poles in the sea to form
    supports
  • poles withdrawn and algae stripped
  • other methods of collection
  • rakes and shovels from small boats, diving
  • taken ashore, dried
  • beaten and shaken to remove sand and shells
  • Bleached by watering and sunlight (removes salt)
  • boiled with acidulated water for several hours
  • mucilaginous decoction filtered through linen
    while hot
  • jelly forms on cooling, cut into bars and forced
    through wire to make strips
  • moisture removed by freezing/thawing, drying at
    35oC and powdering

46
  • Constituents
  • agarase a-D-galacturose 3,6
    anhydro-ß-L-galactose
  • agaropectin (40) D-galactose, D-glucuronic
    acid, L-galactose with sulphate ester groups
  • make a series of polymers
  • at low concentration very viscous stable
    solutions
  • hence low concentrations used as solid gel
  • Uses
  • agar plates, chromatography
  • food industry thickener, emulsifier

47
  • 3 Irish Moss
  • From Chrondus crispus, Gigartina stellata
  • red alga carrageen, Chondrus
  • Similar polymer to agar
  • Uses
  • kappa form has stronger gelling properties,
    emulsifier (for cod-liver oil and other oils),
    holds solid particles in solution as suspensions
  • binder in toothpastes many uses in food industry

48
Use of polymers
  • According to desired properties
  • linear, neutral
  • occupy large space
  • high degree of hydration
  • where low concentration is required
  • precipitate out at high concentration
  • branched, neutral or acidic
  • can use a larger concentration before they
    precipitate
  • gels, pastes etc
  • side chains mean shorter molecule
  • for restricted flow solution
  • use cellulose or carob
  • not pectins, carrageen, acacia, tragacanth -gt
    smooth and viscous solutions
  • carrageen holds particles in suspension
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