FOOD CHEMISTRY-

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FOOD CHEMISTRY-
Polysaccharides

• BY
• DR BOOMINATHAN Ph.D.
• M.Sc.,(Med. Bio, JIPMER), M.Sc.,(FGSWI, Israel),
  Ph.D (NUS, SINGAPORE)
• PONDICHERRY UNIVERSITY
• III lecture
• 8/August/2012

Source Collected from different sources on the
internet and presented b y Dr Boominathan Ph.D.
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Polysaccharides
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Goals Cellulose Starch

• Cellulose structure
• Cellulose ingredients
• Starch structure
• Starch gelatinization
• Modified starches

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b

• Cellulose, a major constituent of plant cell
  walls, consists of long linear chains of glucose
  with b(14) linkages.
• Every other glucose is flipped over, due to b
  linkages.
• This promotes intra-chain and inter-chain H-bonds
  and

van der Waals interactions, that cause cellulose
chains to be straight rigid, and pack with a
crystalline arrangement in thick bundles -
microfibrils.
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• The role of cellulose is to impart strength and
  rigidity to plant cell walls, which can withstand
  high hydrostatic pressure gradients. Osmotic
  swelling is prevented.

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Cotton
Cotton fibres represent the purest natural form
of cellulose, containing more than 90 of this
carbohydrate.
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Cellulose

• Most abundant organic compound on the planet
• Plant cell wall component
• Gives tensile strength to cell wall
• Very high molecular weight insoluble polymer of
  glucose
• ?-1-4 glycosidic bonds
• These bonds give cellulose a very rigid straight
  parallel chain that has extensive H-bonds
• It is mainly used to produce paperboard and
  paper to a smaller extent it is converted into a
  wide variety of derivative products such as
  cellophane and rayon.
• Converting cellulose from energy crops into
  biofuels such as cellulosic ethanol is under
  investigation as an alternative fuel source.

v.s.
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Cellulose
Hydrogen Bond
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Cellulose

• Properties
• Crystalline regions have very tight H-bonding
• Insoluble in water
• No effect on viscosity (why?)
• Little access to hydrolytic reagents and enzymes
• Very tough texture
• Not digestible by humans
• ?-1-4 glycosidic bonds
• Pass through digestive system
• Contributes no calories
• Some ruminants like cows and sheep contain
  certain symbiotic anaerobic bacteria (like
  Cellulomonas) in the flora of the rumen, and
  these bacteria produce enzymes called cellulases
  that help the microorganism to break down
  cellulose
• Dietary fiber
• Improve bowel movements

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Cellulose

• Uses in foods
• Unmodified cellulose is made from wood pulp or
  cotton (dry powder) ? very cheap
• Minimal effect on viscosity
• Added as "fiber" (breads and cereals)
• Non-caloric bulk (no flavor, color etc)
• Very little effect in foods
• Can improve function slightly by heating
• Small number of H-bonds break
• Slight swelling, softening
• Only slightly soluble in water
• No change in digestibility

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Cellulose

• Cellulose can be modified to dramatically improve
  its function and use
• Microcrystalline cellulose (MCC)
• Prepared by partial acid hydrolysis
• Non-crystalline regions are penetrated by acid
  and cleaved to release the crystalline regions
• Crystalline regions combine to form microcrystals
  
• Still insoluble (all crystalline)
• Limited food uses
• Stabilizes emulsions
• Absorbs oils syrups
• Dry mixes - keeping them free-flowing

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Cellulose Microcrystalline cellulose (MCC)

• Two main products of MCC
• Powdered MCC
• Spray dried MCC
• Forms aggregated porous/sponge-like microcrystals
• Uses
• Flavor carrier
• Anticaking agent in powders and cheese

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Cellulose

• Colloidal MCC
• Mechanical energy applied after hydrolysis to rip
  microcrystals apart to form small
  micro-aggregates
• Water dispersible similar function as food gums
• Food uses
• Foam and emulsion stabilizer
• Pectin and starch stabilizer
• Fat and oil replacement

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Cellulose

• B) Methyl cellulose
• Cellulose treated with NAOH to swell fibers and
  then methyl chloride is introduced
• Get methyl ether group

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Cellulose Methyl cellulose

• Unique results
• Soluble in cold water
• Methyl ether group breaks H-bonding
• Solubility ? as temperature ?
• Heating dehydrates the cellulose and hydrophobic
  methyl ether groups start to interact
• Viscosity increases and methyl cellulose forms a
  gel
• Becomes soluble again on cooling

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Cellulose Methyl cellulose

• Food uses
• Thermogelation properties
• Fat/oil barrier in batters for deep fried food
  applications
• The cellulose gels on heating and prevents fat
  uptake
• Holds moisture in food during thermal processing
• Acts as binder during thermal processing
• Fat replacer
• Methyl ether groupgives it fat-like
  properties
• Emulsion and foam stabilizer
• Due to increased viscosity (thickening effect)
• Film forming ability (e.g. water soluble bags)

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Cellulose

• C) Carboxymethyl cellulose (CMC)
• Cellulose treated with NaOH
• to swell fibers and then
• chloroacetic acid is
• introduced
• Get carboxymethyl ether
• group

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Cellulose Carboxymethyl cellulose

• Food use
• Major use non-digestible fiber in dietetic foods
• Hot and cold water soluble
• Weak acid ? properties affected by pH due to
  carboxyl group
• COOH ? COO-
• Negative charge leads to repulsion between CMC
  making it a good thickening and stabilizing agent
• ?repulsion ?viscosity

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Cellulose Carboxymethyl cellulose

• Food uses (cont.)
• Common stabilizer in ice cream
• Retards ice crystal formation
• Foam stabilizer
• Tends to interact with proteins due to charge,
  increasing their viscosity solubility
• Used to stabilize milk proteins in milk
• Can form gels and films

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Hemicellulose

• Hemicellulose is a polysaccharide related to
  cellulose that comprises nearly 20 of the
  biomass of most plants.
• In contrast to cellulose, hemicellulose is
  derived from several sugars in addition to
  glucose, especially xylose but also including
  mannose, galactose, rhamnose, and arabinose.
• Hemicellulose consists of shorter chains around
  200 sugar units. Furthermore, hemicellulose is
  branched, whereas cellulose is unbranched.

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Bio-fuel Ethanol Production Today
BRAZIL
sugarcane
(sucrose)
Sugars
ethanol
extract
ferment
USA
(starch)
Cosgrove, 2006
Sugars
ethanol
Hydrolyze(enzymes)
ferment
Brazil and the US are the leaders in ethanol
fuel production They use the easy way to make
ethanol.
Todays ethanol production is from sugar
(mostly cane and beets) and starch (corn in the
US, wheat and barley in Europe). Yeast will
ferment that sugar into ethanol.
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Chemical structure of starch
STARCH
Starch is the storage molecule plants use to
provide energy for seedling germination and
growth. It is a simple repeating chain of
glucose molecules, a six carbon sugar that can be
easily fermented. Starch is easy to break down
into glucose, using heat and the readily
manufactured enzyme amylase.
http//www.ucmp.berkeley.edu/monocots/corngrainls.
jpg
http//www.scientificpsychic.com/fitness/carbohydr
ates1.html
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The rest of the plant is mostly sugar too!
3 nm
Most people arent aware that woody biomass,
leaves and stalks area about 70 sugar. That
sugar is locked up in cellulose and hemicellulose
the polymers that compose the plant cell
wall..
Polymerized glucose
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The rest of the plant is mostly sugar too!
Cellulose is also a chain of glucose, a 6
carbon sugar, while hemicellulose contains both 5
and 6 carbon sugars. Cellulose contains more
complex chemical bonds of alternating glucose
units, requiring three different enzymes to
break apart. And the 5 carbon sugars are a
bit tricky to convert to ethanol a topic that
we will discuss in a moment
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Plant cell wall
Cell walls fuel
Cellulose,Hemicellulose, lignin
recalcitrance
Cellulose microfibril
chemical pretreatments
Parallel strands of glucose polymers
Cosgrove, 2006
Not cost effective Extensive research is ongoing
to reduce the costs
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Cell walls fuel

• The difficulty in breaking down plant cell walls
  into sugars is called recalcitrance. Current
  methods to address recalcitrance depend on
  relatively expensive enzyme cocktails after a
  high temperature pretreatment that often includes
  acid or alkaline chemicals to break down lignin.
  
• Pretreatment costs account for about 1/3 of the
  conversion process, while enzymes might add
  another 20 to the ethanol cost. Extensive
  research is ongoing to reduce both of these
  costs.

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Components of plant cell walls
This is the breakdown of typical plant cell
walls. Biochemical strategies can convert the
cellulose and hemicellulose to ethanol, while the
residual lignin would most likely be burned to
provide heat and power for the biorefinery, and
export electricity to the grid.
Cellulose
Cellulose (6 carbon sugars)
Lignin
Lignin (phenols)
Extractives
Extractives
Hemicellulose (both 5 and 6 carbon sugars) (need
modified microbe to convert to ethanol)
Ash
Ash
Chapple, 2006 Ladisch, 1979, 2006
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Ethanol from glucose or xylose
Jeffries Shi Adv. Bioch Eng 65,118
To convert the 5 carbon sugars from hemicellulose
into ethanol requires a number of complex steps.
A few microorganisms have been modified so that
that can ferment both the 5 and 6 carbon sugars
into fuels this slide illustrates one of
several strategies that have been tried.
Licensing an effective co-fermenting organism
(or organisms) is likely to be a critical factor
in and business becoming a cellulosic ethanol
success.
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Bio-fuel Ligno-Cellulosic Ethanol Fact Sheet
http//www.neeic.org
Cellulosic Ethanol Production Most plant matter
is not sugar or starch, but cellulose,
hemicellulose, and lignin. The green part of a
plant is composed nearly entirely of these three
components. To convert cellulose to ethanol, two
key steps must occur

• Benefits of Cellulosic Ethanol
• Access to wider array of potential feedstock,
  including waste cellulosic materials and
  dedicated cellulosic crops.
• Greater avoidance of conflicts with land use for
  food production
• Greater displacement of fossil energy per litre
  of fuel, due to nearly completely biomass-powered
  systems.
• Much lower net greenhouse gas emissions than with
  grain-to-ethanol production powered primarily by
  fossil energy.

Cellulosic Materials Agricultural Waste, Forest
Waste, Municipal Solid Waste Dedicated Energy
Crops

1. Saccharification A variety of thermal, chemical,
   and biological processes are used to break
   cellulose down into sugars. This step is a major
   challenge.
2. Fermentation The sugars must be fermented to
   make ethanol, similar to the grain-to-ethanol
   process.

Greenhouse Gas Reduction Impacts Producing
ethanol from cellulosic feedstock has the
potential to achieve greater greenhouse gas (GHG)
reductions than grain-based ethanol. The use of
cellulosic feedstock in producing ethanol has a
double value in that the left over (mainly
lignin) parts of the plant can be used as process
fuelto fire boiler fermentation systems. This
makes for both a relatively more energy-efficient
production process and amore renewable approach
since fossil energy use for feedstock conversion
can be kept to a minimum. Typical estimates for
net GHG emissions reduction from production and
use of cellulosic ethanol are in the range of 70
to 90 compared to conventional gasoline. Net GHG
reductions can be boosted even further if the
electricity produced by cogeneration facilities
is used to displace coal-fired power on the grid.
Production
Costs Cellulosic ethanol requires much greater
processing than grain or sugar-based ethanol, but
feedstock costs for grasses and trees are
generally lower. If targeted reductions in
conversion costs can be achieved, the total costs
of producing cellulosic ethanol could fall below
that of grain ethanol. There are no large-scale
commercial cellulosic ethanol plants currently in
operation, by the National Renewable Energy
Laboratory estimates that in the near-term, it
would cost a large-scale facility about 1.36 per
gallon to produce cellulosic ethanol. The
Department of Energy (DOE) has set a goal of
bringing down the overall production costs to
1.07 per gallon by 2012.
Gasification Gasification
is an alternative production technology that
does not rely on chemical decomposition of the
cellulose. Instead of breaking the cellulose
into sugar molecules, the carbon in the raw
material is converted into synthetic gas
(syngas), a mixture of carbon monoxide and
hydrogen. The syngas can then be converted to
diesel (via Fischer-Tropsch (FT) synthesis),
methanol, or dimethyl ether- a gaseous fuel
similar to propane. Alternatively, the hydrogen
can be separated and used as fuel. Currently,
most interest exists in the production of diesel
via FT synthesis- the same technology used in
gas-to-liquids and coal-to-liquids plants.

• Research Initiatives
• Millions of research dollars are focused on
  developing more efficient separation, extraction,
  and conversion techniques.
• A key research area is enzymatic hydrolysis
  processes, which is believed to have the
  potential to improve the efficiency and lower the
  cost of cellulosic ethanol production.
• The DOE recently awarded grants totaling 385
  million over 4 years in 6 companies working on
  cellulosic ethanol plants.
• The Department of Agriculture is seeking to
  increase its bioenergy financing to 161 million
  from 122 million, including 21 million in loan
  guarantees for cellulosic ethanol plants.
• In the early part of 2007, venture capital firms,
  Wall Street, and even oil companies have invested
  approximately 200 million in cellulosic ethanol
  development.