Food Carbohydrates

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Food Carbohydrates
OLIGOSACCHARIDES
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Definition

• Oligo- few in Greek oligosaccharides
  contains 1-10 (20)
• monosaccharide uints. Polysaccharides gt10 or
  20.
• Oligomers, polymers -mer designates a structure
  composed of parts.

• Poly- many in Greek

• In disaccharides, the aglycon is a
  monosaccharide unit

• Higher order oligosaccharides are named tri-,
  tetra-,
• penta-, hexa-, hepta-, etc.

• Structures may be predominately linear or
  branched.

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Structural features
Linear a head to tail linkage 1 reducing
end 1 non-reducing end
Glycosyl unit
Branched 1 reducing end several to many
non-reducing ends
reducing end
non-reducing end
Glycosidic linkage of anomeric carbon and OH of
another unit
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Glycosidic linkages

• Carbohydrates are polyalcohols ? -OH can react
  with a
• hemiacetal -OH to split out water and form a
  glycosidic
• bond between two residues.

• Take D-glucopyranose as an example
• ?-D-glucopyranose could react with OH at
  C-2, C-3,
• C-4 and C-6 of the 2nd unit ? 4 reducing
  disaccharides
• ?-D-glucopyranose ????? 4
• ?- and ?- hemiacetal hydroxyl groups of two
  residues could
• react with each other ?? 3 nonreducing
  disaccharides
• Total 11 possible disaccharides

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Acid-catalyzed reversion

• Glycosic bonds can be hydrolyzed with acid and
  heat.
• The reaction is reversible, sugars re-combine
  in the
• presence of acid and water-limiting
  conditions to form
• mixture of oligomers.

• This acid-catalyzed combination of
  monosaccharides is
• called reversion. Glycosidic linkage can
  occur at any
• OH position (at O-2,O-3 etc) and in ? or ?
  configuration.
• Example conversion of maltose to cellobiose

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Acid-catalyzed reversion
?-1,4 linkage
Maltose
2 glucans
Cellobiose ?-1,4 linkage
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Acid-catalyzed reversion
This random reaction has been used for
commercial production of the bulking agent
Polydextrose
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Polydextrose

• Polydextrose is produced by the reversion
  reaction
• between D-glucose, sorbitol and citric acid
  under heat
• treatment.
• Degree of polymerization (DP) is fairly low.
• Sold commercially as Litesse and other names.

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Maltose

• Full name 4-O-(?-D-glucopyranosyl)-D-glucopyrano
  se
• Exists as ?- and ?-anomers.

• Reducing sugar. Its glycosidic linkage is acid
  labile.

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Maltose

• Obtained from starch by
• - acid hydrolysis (randomness, low yield)
• - ?-amylase (from Bacillus bacteria)
• Yield 80, higher yield by the action of
• debranching enzymes and then
  ?-amylase.

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Maltose

• Maltose is crystallized easily from aqueous
  solution as
• ?-maltose monohydrate, even though in
  solution the
• ratio of ? to ? forms is 12.

• Maltose uses mild sweetener for foods and
• pharmaceuticals, and as a parenteral
  injectable
• for slow release of D-glucose.

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Lactose

• Name 4-O-(?-D-galactopyranosy)-
• D-glucopyranose

• Reducing sugar
• Hydrolyzable with acid
• Multiple anomeric forms in solutions

• Lactose (milk sugar) 2.0-8.5
• cow/goat milk 4.5
• human milk 7.0

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Lactose production
(as ?-lactose monihydrate)
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Lactose production

• 1pound of cheese ? 9 lbs whey (4.7 lactose) ?
• ? 0.4 lb lactose

• Potential lactose production from whey 23
  billion
• pounds per year!
• Unfortunetely, little commercial use at this
  time.

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Lactose uses

• Food toppings, icings, pie fillings,
  confections,
• ice cream
• In food, lactose contributes body but little
  sweetness
• (20 of sucrose), enhances colors and flavors.

• Pharmaceutical uses provides bulk and rapid
  dissolution

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Lactose/Lactate

• Lactose is relatively high in milk and milk
  products but
• lower in fermented dairy products as yogurt,
  cheeses.
• During fermentation, some lactose is converted
  to
• L-lactate

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Lactose intolerance (L.I.)

• Lactose is digested in small intestine by the
  hydrolytic
• enzymes lactase (?-galactosidase) located in the
  
• brush border epithelial cells.

• If lactose is not completely hydrolyzed and
  absorbed,
• it will proceed into the large intestine wher
  anaerobic
• bacteria ferment the lactose to lactic acids,
  other short
• chain acids, CO2, H2 and methane.

• This causes the symptom of lactose intolerance
• abdominal distention, flatulence, cramping,
  diarrhea.

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Lactose intolerance

• Usually not seen in lt 6 years old children. The
  L.I.
• people increases with age (highest among the
  elderly).

• Low among Western European Americans (6-25),
• high in other populations (50-75).

• Suggest that production of lactase is under
  genetic control.

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Dealing with lactose intolerance

• Reduce lactose by fermentation (yogurt,
  buttermilk etc.)

• Add lactase to lactose containing foods just
  before consuming
• (or consume lactase).

• Novel technology add live yogurt cultures to
  refrigerated milk,
• the bacteria release lactase upon
  reaching the small intestine.

• Reduce lactose to lactitol (hydrogenation with
  H2), or isomerize
• in alkaline to lactulose (keto sugar).
  Lactitol and lactulose are
• not absorbed by small intestine and are
  fermented to lactic and
• acetic acids. The water attracting
  properties of these acids soften
• stools and facilitate bowel function.

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Sucrose

• Sucrose structure an exception to the general
  rule for oligo- and
• polysaccharides, glycosyl units are linked
  head-to-head
• (reducing end to reducing end

• Non-reducing sugar CHO- of D-glucosyl unit and
  CO of
• D-fructosyl unit are in glysosidic bond, no
  reducing end.

• The glycosidic bond is high energy, unstable
  (partly due to the
• strained fructofuranosyl ring.

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Sucrose

• As a result, sucrose is easily hydrolyzed in
  very dilute acid
• or enzymes

H
Sucrose
Glucose Fructose
invertase (yeast, bacteria) or intestinal sucrase
invert sugar (equimolar mixture of D-glucose and
D-fructose)
?D 66.5?
?D -33.3?
invertase?-D-fructofuranosidases, leaves O atom
with D-glucose sucrase ?-D-glucosidase, leaves O
atom with D-fructose
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Sucrose and invertase
sucrase leaves oxygen atom with
D-fructose invertase leaves oxygen atom with
D-glucose
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Sucrose sources

• Sucrose is synthesized mainly in plant leaves,
• then transported throughout the plant,
• and stored in stems, roots ot tubers.
• Sources sugar cane and sugar beet
• Processing steps involve crushing/extracting,
  
• treating with lime, heating, filtration and
• crystallization and refining treatments
• (for decolorizing and recrystallizing)

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Sucrose properties and uses

• Sucrose is very soluble in water (67g per 100 g
  solution at 20?C),
• can form highly concentrated solutions (syrups,
  honey).
• Uses sweetener, preservative, humectant

• Cryoprotectant function as water crystallizes,
• sucrose increases
• freezing point decreases
• viscosity of the remaining solution increases.
• Eventually, the liquid phase solidifies as a
  glass (vitrification). This
• explains how some carbohydrates can protect
  against dehydration
• via crystallization) that destroy structure
  and texture by freezing.

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Sucrose structure in solution crystals
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Sucrose Derivatives Sucrose Esters

• Sucrose molecule has a very rich potential
• non-reducing, stable,pure, cheap polyol
• various reactions oxidation, reduction,
  esterification etc.

• Sucrose esters
• low esterification (1-3 fatty acids, e.g.
  stearic acid)
• ? surfactants (emulsifiers)
• fully acetylated sucrose (sucrose octaacetate)
• ? very bitter, use to denature ethanol
• with long chain fatty acids (8-12 carbon atoms),
  6-8 fatty acids
• (hexa-, hepta- and octa-ester)
• ? not metabolized or absorbed
• e.g. OLESTRA (low-calorie fat substitute)

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Structure of sucrose polyesters

• Esssential structural characteristics
• apolar part fatty acids
• polar part non-esterified hydroxides of sucrose
• and glycerol (sucroglycerides)
• ? different hydrophilic-lipophilic balance (HLB
  value)

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Sucralose

• Chlorinated sucrose with a D-galactopyranosyl
  unit in place
• of the normal D-glucopyranosyl unit.

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Sucralose
600 x sweeter than sucrose, good taste quality
Adequate water solubility Not hydrolyzed in
small intestine 60 x more stable to acid than
sucrose Approved for use in the US since 1998

• Uses tabletop sweetener, beverages, baked
  goods, chewing
• gums, dry mixes, fruits spreads, frozen
  desserts.

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Isomaltulose

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Isomaltulose (Isomalt, Palatinose)

• Prepared by enzyme-catalyzed transfer of the
  glycosidic linkage
• from O-2 to O-6 in the D-fructopyranosyl unit.
• Enzyme is produced by Protaminobacter rubrum.
• ½ sweetness of sucrose.
• Uses (in Europe) noncariogenic candies,
  specialty chocolate,
• chewing gums, cookies

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Isomaltitol(Palatinit)

• Hydrogenation of isomaltulose with hydrogen and
  a catalyst
• ? Palatinit
• Crystalline, about 45 as sweet as sucrose.

GPM?-D-Glc-(1?6)-D-manitol
GPS?-D-Glc-(1?6)-D-sorbitol
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Leucrose

• Leucrose is a reducing disaccharide

• Produced by Leuconostoc mesenteroides
• 50 as sweet as sucrose

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Kestose and Neosugar
Kestose (GF2)
Fructosefuranosyl nystose (GF4)
Nystose (GF3)
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Kestose and Neosugar

• Preparation of kestose and neosugar A
  concentrated solution of
• sucrose is treated with invertase or a fungal
  transferase.
• This causes the transfer of D-fructosyl units
  onto sucrose.
• 50 as sweet as sucrose.
• Non-cariogenic, approved for use in Japan.

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Inulin

• Structure condensation of hundred units of
• D-fructose, by means of ??-2?1 bonds,with
• a few D-glucose units at the end.

• Inulin properties
• - its gelling capacity can improve emulsion
  stability
• - non-digestibility, behaves as dietary
  fiber, and is
• hydrolyzed by bacteria in the colon
  (bifidobacteria
• lactobacilli)
• - low caloric value (4-10 kJ/g)
• Uses as fat substitute and dietary fiber for
  low-calorie
• foods (40 inulin 60 water, with high shear
• ? network trapping water molecules, stabilizing
• emulsions)

n-1
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Trehalose
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Trehalose

• Found in animals and plants that are known as
  anhydrobiotic, (survive drying and
  freezing, e.g. frogs, desert plants, insects).
  Trehalose molecule fits into the gap in polymer
  structure vacated by water and maintains the
  necessary H- bonds that support the proetin and
  membrane structure.

• Extraction of trehalose from plant/animal
  tissues is impractical.
• Its now feasible to hydrolyze starch to
  trehalose by
• fermentation with yeasts, bacteria.
• Commercial trehalose syrups are being used to
  preserved dried
• and frozen foods.
• Current issue is trehalose really a better
  stabilizer?

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Rafinose and Stachyose

• Mostly from beans and other legumes, sugar beet
  extract
• Cause flatulence

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Rafinose