Polysaccharides Individual Polysaccharides
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Transcript of Polysaccharides Individual Polysaccharides
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It is a gelatinous product isloated from seaweed ( red algae, class Rhadopycasae ) by hot
water extraction process.
Structure:
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The structure is composed of the components of the chain -D-
galactopyranose and 3,6-anhydro- -L-galactopyranose .
Property:
Hysteresis it means theres a lag between the solidification of the agar which
needed to be incubated for solidifying from 32 40oC and melting at 85oC
Indigestible
heat resistant gels
Utilization:
use in cultivating microorganisms
Stabilizes yoghurt, some candy and baked products
role in vegetarian diets as a meat substitute products
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Alginate or algin also called as alginic acid is an anionic polysaccharide distributed
widely in the cell walls of brown algae, where it, through binding water, forms a viscous
gum. The major source of production is the giant kelp.
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Structure:
Alginate building blocks are -D-mannuronic and -L-guluronic acids, joined by 14
linkages:
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Properties:
Alginates are water soluble in the form of alkali, magnesium, ammonia or amine salts.
Viscosity-Gelatinous formaition occur when Ca or acids is added to Na-alginate solutins.
Utilization:
Act as a thickener, stabilizing ang gel- forming agent.
Prevents formation of larger ice crystals in ice creams during storage.
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It is a family of linear sulfated polysaccharide that are extracted from red
seaweeds.
TYPES:
Kappa forms strong, rigid gels in the pressence of potassioum ions. Can be
extracted from Eucheuma cottonii.
Iota forms gel in the pressence of calcium ions, main source is the Eucheumaspinosum
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Lambda used in thickening dairy products, mainly source is the Gigartina
The primary differences that influence the properties of kappa, iota, and
lambda carrageenan are the number and position of the ester sulfate groups on therepeating galactose units. Higher levels of ester sulfate lower the solubility
temperature of the carrageenan and produce lower strength gels, or contribute to gel
inhibition (lambda carrageenan).
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Properties:
Solubility - All carrageenan types are soluble in hot water at temperatures above its gel melting temperature.
Gelling - Hot aqueous solution of kappa and iota carrageenans have the ability to form thermo-reversible gels
upon its cooling.
Viscosity - The viscosity of carrageenan solutions should be determined under conditions where there are no
tendencies for the solution to start gelling. When a hot carrageenan solution is cooled, the viscosity increases
gradually until the gelling temperature is reached. As the gel starts to form, there is a sudden and a very
substantial increase in viscosity. Therefore, the viscosity measurements of carrageenan solutions should be
determined at sufficiently high temperatures (75 C) to avoid the effect of gelation.
Stability - Carrageenan solutions are quite stable at neutral or alkaline pHs. At lower pHs their stability
decreases, especially at high temperatures. As the pH is lowered hydrolysis of the carrageenan polymer
occurs, resulting in loss of viscosity and gelling capability.
Utilization:
In chocolate milk prevents fat droplet separation and stabilizes the suspension of cocoa.
The gelling property in the presence of K+ salt is utilized in desserts and cannedmeat.
Carrageenans are also used to stabilize ice cream
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Furcellaran
Furcellaran (Danish agar) is produced from red sea weed (algae Furcellaria fastigiata).Production began in 1943 when Europe was cut off from its agar suppliers. After alkali
pretreatment of algae, the polysaccharide is isolated using hot water.
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Structure:
Furcellaran is composed of D-galactose (4653%), 3,6-anhydro-D-galactose
(3033%) andsulfated portions of both sugars (1620%).The structure of furcellaran is
similar to -carrageenan.The essential difference is that -carrageenanhas one sulfateester per two sugarresidues, while furcellaran has one sulfate ester residue per three to
four sugar residues. Sugar sulfates identified are: D-galactose-2-sulfate,-4-sulfate and -
6-sulfate, and 3,6-anhydro-Dgalactose-2-sulfate. Branching of the polysaccharide chain
can not be excluded. Furcellaranf orms thermally reversible aqueous gels by a
mechanism involving double helix formation,similar to -carrageenan.
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Properties:
Addition of sugar affects the gel texture, which goes from a brittle to a more elastic texture.
The gelling ability is affected by the polysaccharide polymerization degree, amount of 3,6-
anhydro-D-galactose, and by the radius of the cations present. K+, NH+4 , Rb+ and Cs+ form verystable, strong gels.
Utilization:
Furcellaran, with milk, provides good gels and therefore it is used as an additive in
puddings. It is also suitable for cake fillings and icings. In the presence of sucrose, it gels
rapidly and retains good stability, even against food grade acids.
Furcellaran is also utilized in processed meat products, such as spreadable meat pastesand pastry fillings. It facilitates protein precipitation during brewing of beer and thus
improves the final clarification of the beer.
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GUM ARABICGum arabic is a tree exudate of variousAcacia species, primarilyAcacia Senegal, and is obtained as a result
of tree bark injury.
Structure:
it is a mixture of polysaccharides and glycoproteins, used promarily in food
industry as a stabilizer. Gum arabic consists mainly of high-molecular weight
polysaccharides and their calcium, magnesium, and potassium salts, which on
hydrolysis yield arabinose, galactose, rhamnose, and glucuronic acid.
Properties:
Solubility insoluble in ethanol
Utilization:
Gum arabic is used as an emulsifier and stabilizer, e. g., in baked products. It retards sugar crystallization
and fat separation in confectionery products and large ice crystal formation in ice creams.
can be used as a foam stabilizer in beverages.
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Gum GhattiIt is mainly consists of polysaccharides, obtained from the
exudation of Agoneissus latifolia which is found in Indiaand Ceylon. It occurs as a gray to reddish-gray powdergranular or light to dark brown lump and almost odorless.
>STRUCTURE:
Gum Ghatti is composed ofL-arabinose, D-galactose,D-
mannose, D-xylose, and D-glucuronic acid. L-Rhamnose hasalso been detected. The sugars are partially acetylated(5.5% acetyl groups based on dry weight). It is soluble inwater to the extent of ca.90% and dispersible.
>USAGEIt is extensively use industrially as thickener and
emulsifier.
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Gum Tragacanth
A microcephalus, contain a gummy, mucilaginous
sap that is the source of gum tragacanth. It is the
exuded gum, which tends to form ribbons
similar in appearance to a goat horn. It is a water-
soluble polysaccharide.
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>STRUCTURE:
Gum tragacanth consists of a water-soluble
fraction, the so- called tragacanthic acid, and the insolubleswelling component, bassorin. Tragacanthic acid contains 43%
of D-galacturonic acid, 40%
of D-xylose, 10% of L-fucose, and 4%of D-galactose. Like
pectin, it is composed of a main
polygalacturonic acid chain which bears side chains made of
the remaining sugar.
The effect of shear rate on viscosity of aqueous tragacanthsolutions.
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A Flake form tragacanth, 1%; b tragacanth, ribbon form, 0.5%
(according to Whistler, 1973) residues. Bassorin consists of
75% of L-arabinose, 12% of D-galactose, 3% of D-galacturonic acid methyl ester, and L-rhamnose.
Its molecular weight is about 840 kdal. The molecules are
highyl elongated (4501.9 nm) in aqueous solution and are
responsible for the high viscosity of the solution.
>USAGE:
Gum tragacanth is used as a thickening agent and a
stabilizer in salad dressings (0.41.2%) and in fillings andicings in baked goods. As an additive in ice creams
(0.5%), it provides a soft texture.
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Karaya GumKaraya gum, also called Indian tragacanth, is an exudate from
an Indian tree of the Sterculia ureus and other Sterculia
species. Unground product: occurs in tears of variable size
and in broken irregular pieces having a characteristic semi-
crystalline appearance; pale yellow to pinkish brown;
translucent and horny.
Powdered product: pale grey to pinkish brown; a distinctive
odour of acetic acid. Items of commerce may containextraneous materials such as pieces of bark which must be
removed before use in food.
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>STRUCTURE:
It composed of D-galactose, L-rhamnose, D-galacturonic
acid, and L-glucuronic acid. The sugars are partially
acetylated (13% acetyl groups based on dry weight). Thispolysaccharide is insoluble in water and resistant to
enzymes and microorganisms. However, it swells greatly
even in cold water. Suspensions have a pasty consistency
at concentrations of more than 3%.> USAGE:
Karaya gum is used as a water binder (soft cheese), a bindingagent (meat products like corned beef, sausages), astabilizer of protein foams (beer, whipped cream,meringues), and as a thickener (soups, sauces, saladdressings, mayonnaise, ketchup).
It increases the freeze-thaw stability of products,
prevents synaeresis of gels, and provides body.
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Guaran/Guar GumGuar flour is obtained from the seed endosperm of the
leguminous plant Cyamopsis tetragonoloba. The seed is
and the germ removed. In addition to the polysaccharide
guaran, guar flour contains 1015% moisture, 56% protein,
2.5% crude fiber and 0.5 0.8 ash. Guar gum is a white toyellowish white powder and nearly odorless.
>STRUCTURE:
Guaran gum consists of a chain of -Dmannopyranosyl
units joined by 1 4 linkages. Every second residue has a
side chain, a D-galactopyranosyl residue that is bound to the
main chain by an (1 6) linkage.
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It is soluble in hot and cold water and has stronf hydrogen
properties.
>USAGE:Guaran gum is used as a thickening agent and a stabilizer in
salad dressings and ice creams (application level 0.3%). In
addition to the food industry, it is widely used in paper,
cosmetic and pharmaceutical industries. In pastry fillings, it
"weeping" (syneresis) of the water in the filling, keeping the
pastry crust crisp.
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Locust bean Gum
The locust bean (carob bean; St. Johns bread) is from an
evergreen cultivated in the Mediterranean area sincetimes. Its long, edible, fleshy seed pod is also used as
fodder. The dried seeds were called carat by Arabs and
served as a unit of weight (approx. 200 mg ). The locustbean seeds consist of 3033% hull material, 2325%
germ and 4246% endosperm. The are milled and the
endosperm is separated and utilized like the guar flour
described above. The commercial flour contains 88%
galactomannoglycan, 5% other polysaccharides, 6%
protein and 1% ash.
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>STRUCTURE:
The main locust bean polysaccharide is similar to that of
guaran gum: a linear chain of 1 4 linked -D-
mannopyranosyl units, with -D-galactopyranosyl residues
1 6 joined as side chains. The ratio mannose/galactose is3
to 6; this indicates that, instead of every second mannose
residue, as in guaran gum, only every 4th to 5th issubstituted
at the C-6 position with a galactose molecule. Themolecular
weight of the galactomannan is close to 310 kdal. Physicalproperties correspond to those of guar gum, except the
viscosity of the solution is not as high.
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>USAGE:
Locust bean flour is used as a thickener, binder and stabilizer
in meat canning, salad dressings, sausages, soft cheeses andice.
It also improves the water binding capacity of dough,
especially when flour of low gluten content is used.
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TAMARIND FLOUR
Occurrence, Isolation
Its brown pods contain seeds which are rich ina polysaccharide that is readily extracted with hotwater and, after drying, recovered in a powderedform.
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Structure
The polysaccharideconsists of D-galactose, D-xylose
and D glucose, withrespective molarratios given inbrackets. L Arabinose
is also present.
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Properties
The polysaccharide forms a stable gelover a wide pH range.
Less sugar is needed to achieve a desiredgel strength than in corresponding pectin
gels.
The gels exhibit only a low syneresis
phenomenon.
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Utilization
The tamarind seed polysaccharide is asuitable substitute for pectin in the production ofmarmalades and jellies.
It can be used as a thickening agent andstabilizer in ice cream and mayonnaiseproduction.
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Arabinogalactan fromLarchOccurrence, Isolation
Coniferous larch-related woods contain a
water-soluble arabinogalactan of 535% of thedry weight of the wood.
It can be isolated from chipped wood by a
counter-current extraction process, usingwater or dilute acids.
The extract is then usually drum dried.
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Structure
The polysaccharide consists of straight chain -D-galactopyranosyl units joined by 1 3 linkages and,in part, has side chains of galactose and arabinoseresidues bound to positions 4 and 6.
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The polysaccharide is highly branched.
The molecular weight is 5070 kdal.
The molecule is nearly spherical in shape, so itsaqueous solution behaves like a Newtonian fluid.
The viscosity is exceptionally low.
The viscosity is practically unaffected by pH.
The solution acquires a thick paste consistency onlyat concentrations exceeding 60%.
Properties
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Arabinogalactan, due to its good solubilityand low viscosity
Used as an emulsifier and stabilizer
A carrier substance in essential oils,
aroma formulations, and sweeteners.
Utilization
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PectinOccurrence, Isolation
Pectin is widely distributed in plants.
It is produced commercially from peels of citrus fruitsand from apple pomace. It is 2040% of the dry mattercontent in citrus fruit peel and 1020% in apple pomace.
Extraction is achieved at pH 1.53 at 60100 C.
The extract is concentrated to a liquid pectin product oris dried by spray- or drum-drying into a powered product.
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StructurePectin is a polysaccharide mixturewith a complicated structure
containing at least 65% ofgalacturonic acid (GalA). Threestructural elements are involved inthe make-up of a pectin molecule:a homogalacturonan (cf. Formula4.147) consisting of (1 4) linked-D-GalA, a galacturonan withdifferently arranged side chains(building blocks: apiose, fucose,arabinose, xylose), and arhamnogalacturonan with a
backbone consisting of thedisaccharide units [ 4)--D-GalA-
(1 2)--L-Rha-(1 ] and with itsrhamnose residueslinked byarabinan and galactan chains.
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At a pH of about 3, and in the presence of Ca2+ ions also athigher pHs, pectin forms a thermally reversible gel.
The gel-forming ability, under comparable conditions, is directlyproportional to the molecular weight and inversely proportional tothe esterification degree.
For gel formation, low-ester pectins require very low pH valuesand/or calcium ions, but they gelatinize in the presence of arelatively low sugar content.
Apart from the degree of esterification, gel formation is alsoinfluenced by the distribution of the ester groups in the pectinmolecule.
Properties
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Utilization
It is widely used in marmalade and jellyproduction.
Standard conditions to form a stable gel are, for
instance: pectin content
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StarchStarch is widely distributed in various plant organs as astorage carbohydrate.
Starch obtained from corn, potatoes, cassava, andwheat in the native and modified form accounted for99% of the world production in 1980.
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The plant material is disintegrated, the starch granules are washed out with
water, and then sedimented from the starch milk suspension and dried.
The protein and starch are then separated in hydrocyclones. Theseparation is based on density difference (protein < starch).
Starch is a mixture of two glucans, amylose and amylopectin
The amylose can be isolated from starch, e. g., by crystallization of astarch dispersion, usually in the presence of salts (MgSO4) or by
precipitation with a polar organic compound (alcohols, such as n-butanol,or lower fatty acids, such as caprylic or capric), which forms a complexwith amylose and thus enhance its precipitation.
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Structure and Properties of Starch
GranulesStarch granules are formed in the amyloplasts.
These granules are simple or compound and consist of concentricor eccentric layers of varying density. They are of varying size (2
150 m), size distribution, and shape .
They are examined by using various physical methods, includinglight microscopy, small-angle light scattering, electron microscopy, X-ray diffraction, small-angle neutron scattering, and small-angle X-rayscattering.
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Starch granules are said to have a semicrystalline character, which
indicates a high degree of orientation of the glucan molecules.
About 70% of the mass of a starch granule is regarded as amorphousand ca. 30% as crystalline.
The amorphous regions contain the main amount of amylose, but alsoa considerable part of the amylopectin.
The course of gelatinization depends not only on the botanical origin ofthe starch and the temperature used, but also on the water content of the
suspension.
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Dried starch with 13% of water undergoes only slight
changes up to a temperature of 180 C
Starch with 60% of water completely gelatinizes attemperatures as low as 70 C.
If an aqueous starch suspension is maintained for sometime at temperatures below the gelatinization temperature, aprocess known as tempering
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The number of gelatinized starch granules wasdetermined by microscopy.
Another way to monitor gelatinization as a function oftemperature is to measure the viscosity of a starchsuspension.
It is known that the gelatinization temperature is increasedby polyhydroxy compounds (glycerol, sugar) and decreasedby salts (NaCl, CaCl2)
Lipids also influence the properties of starch.
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Structure and Properties of
AmyloseAmylose is a chain polymer of -D-glucopyranosyl residues linked 14:
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Enzymatic hydrolysis of the chain is achieved by -amylase, -amylase and glucoamylase.
The molecular size of amylose is variable.
It is difficult to bring the postulated antiparallelarrangement of the double helices into line with therequirements of biosynthesis, where a parallelarrangement can be expected. It is possible that thepresent experimental data do not exclude such anarrangement.
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Structure and Properties of
AmylopectinAmylopectin is a branched glucan with side chains attached inthe 6-position of the glucose residues of the principal chain :
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Enzymatic degradation of amylopectin is similar to
that of amylose. The enzyme -amylase degrades themolecule up to the branching points.
The remaining resistant core is designated as
limit-dextrin.
Amylopectin, when heated in water, forms atransparent, highly viscous solution, which is ropy,
sticky and coherent.
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Utilization
Starch is an important thickening and binding agent and is usedextensively in the production of puddings, soups, sauces, salad dressings,diet food preparations for infants, pastry filling, mayonnaise, etc.
Corn starch is the main food starch and an important raw material for the
isolation of starch syrup and glucose
A layer of amylose can be used as a protecting cover for fruits (datesor figs) and dehydrated and candied fruits, preventing their stickingtogether.
Amylose treatment of French fries decreases their susceptibility tooxidationAmylose films can be used for food packaging, as edible wrapping ortubing, as exemplified by a variety of instant coffee or tea products.
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Resistant Starch
Starch and its degradation products which are notabsorbed in the small intestine are called resistant starch(RS).
RS can, however, be metabolized by the bacteria of thecolon.
Acetic acid, propionic acid and butyric acid are formed,
stimulating the growth of the cells of the intestinalepithelium.
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A distinction ismade between 4 forms of
RS:Type I - starch enclosed in cells (e. g., coarse-groundgrain or legumes)
Type II - native starch granules (e. g., in bananas,potatoes)
Type III - starch fractions produced on retrogradation (e.
g., in boiled potatoes, bread crumb)
Type IV - starch modified by the Maillard reaction orcaramelization (formation of glycosidic bonds which arenot hydrolyzed by -amylase).
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MODIFIED STARCHES
are starches that:
are improved or tailored by physical
and chemical methods to fit or adjust
the properties to a particular application
or food product.
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MODIFIED STARCHES
Chemically modified. Primarily they are usedbecause of their technological characteristics andare therefore legally considered as supplements.Their use is thus, as for all supplements, regulated
by legislative provisions.
Physically (e.g. through heat or pressure) orenzymatically modified starches are regarded asingredients and are itemized in the list ofingredients under the term starch.
Table 4.26. Utilization of amylopectin and its derivatives
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Table 4.26. Utilization of amylopectin and its derivatives
Starch Utilization
Unmodified waxy starch (also in
blend with normal starch and
flours)
Salad dressing, sterilized canned and frozen food,
soups, broth, puffed cereals, and snack food
Pregelatinized waxy starch or
isolated amylopectinBaked products, paste (pt) fillings, sterilized
bread, salad dressing, pudding mixtures
Thin boiling waxy starch Protective food coatings
Cross-linked waxy starch Paste fillings, white and brown sauces, broth,
sterilized or frozen canned fruit, puddings, saladdressing, soups, spreadable cream products for
sandwiches, infant food
Waxy starch, hydroxypropyl
ether
Sterilized and frozen canned food
Waxy starch, carboxymethyl
ether
Emulsion stabilizer
Waxy starch acetic acid ester Sterilized and frozen canned food, infant food
Waxy starch succinic- and
adipic acid estersSterilized and frozen canned food, aroma
encapsulation
Waxy starch sulfuric acid ester Thickenig agent, emulsion stabilizer, ulcer treatment(pepsin inhibitor)
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MODIFIED STARCHES
Mechanically Damaged
Starches
Extruded Starches
Dextrins
Pregelatinized Starches
Thin-Boiling Starches
Starch Ethers
Starch Esters
Cross-Linked
Starches
Oxidized Starches
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Mechanically Damaged
Starches Starch granules are damaged by means of grinding or byapplication of pressure at various water contents.
The amorphous portion is increased, resulting in improved
dispersibility and swellability in cold water. Decrease in the gelatinization temperature by 510 C,
and an increase in enzymatic vulnerability.
In bread dough made from flour containing damaged
starch, for instance, the uptake of water is faster andhigher and amylose degradation greater.
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Extruded Starches
Starches that:
are easily dispersible, better soluble, and have
a lower viscosity.
Maltose, isomaltose, gentibiose, sophorose,
and 1,6-anhydroglucopyranose appeared .
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DEXTRINS Heating of starch (
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DEXTRINS
a soluble, gummy substance, formed from starch by the action of heat, acids, orferments, occurring in various forms and
having dextrorotatory properties.
used chiefly as a thickening agent inprinting inks and food, as a mucilage, and as a s
ubstitute for gum arabic and other naturalsubstances.
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Pregelatinized Starch
Heating of starch suspensions, followedby drying, provides products that are
swellable in cold water and form pastesor gels on heating.
These products are used in instant foods,and as baking aids.
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Thin- Boiling Starch
Partial acidic hydrolysis yields a starch product which isnot very soluble in cold water but is readily soluble in
boiling water.
The solution has a lower viscosity than the untreated
starch, and remains fluid after cooling. Retrogradation is
slow.
These starches are utilized as thickeners and as protective
films.
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Starch Ethers
When a 3040% starch suspension is reacted with ethylene
oxide or propylene oxide in the presence of hydroxides of alkali
and/or alkali earth metals (pH 1113), hydroxyethyl- or
hydroxypropyl derivates are obtained (R=H, CH3)
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The derivatives are also obtained in reaction with the
corresponding epichlorohydrins.
Introduction of hydroxyalkyl groups, often in combination with
a small extent of cross-linking greatly improves starch swelling
power and solubility, lowers the gelatinization temperature and
substantially increases the freezethaw stability and the paste
clarity of highly-viscous solutions.
Therefore, these products are utilized as thickeners for
refrigerated foods (apple and cherry pie fillings, etc), and heat-
sterilized canned food.
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Reaction of starch with monochloroacetic acid in an
alkaline solution yields carboxymethyl starch.
These products swell instantly, even in cold waterand in ethanol.
These products are of interest as thickeners andgelforming agents.
St h E t
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Starch Esters
Starch monophosphate ester: producedby dry heating of starch with alkaline
orthophosphate or alkaline
tripolyphosphate at 120175 C
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Starch organic acid esters- acetic acid
- longer chain fatty acids (C6C26)
- adipic or citric acids
obtained in reactions with the reactivederivatives (e. g., vinyl acetate) or by
heating the starch with free acids or theirsalts.
In addition esterified starch has an improved
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In addition, esterified starch has an improved
freezethaw stability. These starches are utilized
as thickeners and stabilizers in bakery products,
soup powders, sauces, puddings, refrigerated
food, heat-sterilized canned food and in
margarines.
The starch esters are also suitable as protective
coatings, e. g., for dehydrated fruits or for aroma
trapping or encapsulation
C i k d S h
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Cross- Linked Starches
are obtained by the reaction of starch (R-OH) with bi-or polyfunctional reagents, such as sodium
trimetaphosphate, phosphorus oxychloride,
epichlorohydrin or mixed anhydrides of acetic and
dicarboxylic acids.
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CROSS- LINKED STARCHES
The starch granule gelatinization temperature
increases in proportion to the extent of cross linking,
while the swelling power decreases. Starch stabilityremains high at extreme pH values (as in the presence
of food acids) and under conditions of shear force.
Cross-linked starch derivatives are generally used
when high starch stability is demanded.
d d h
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Oxidized Starches
Starch hydrolysis and oxidation occur when aqueous
starch suspensions are treated with sodium hypochlorite
at a temperature below the starch gelatinization
temperature range. The products obtained have an
average of one carboxyl group per 2550 glucose residues:
O idi d S h
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Oxidized Starches
Oxidized starch is used as a lower-
viscosity filler for salad dressings and
mayonnaise. Unlike thin-boiling starch,
oxidized starch does not retrograde nor
does it set to an opaque gel.
CELLULOSE
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CELLULOSE
Occurrence and Isolation Cellulose is the main constituent of plant cell
walls, where it usually occurs together withhemicelluloses, pectin and lignin.
Cellulose together with some other inertpolysaccharides, constitute the indigestiblecarbohydrate of plant food (vegetables, fruitsor cereals), referred to as dietary fiber.
The importance of dietary fiber in humannutrition appears mostly to be themaintenance of intestinal motility (peristalsis).
STRUCTURE
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STRUCTURE
Cellulose consists of -glucopyranosylresidues joined by 14 linkages.
STRUCTURE
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STRUCTURE
Cellulose crystallizes as monoclinic, rod-likecrystals. The chains are oriented parallel to thefiber direction and form the long b-axis of the unitcell.
Intermolecular hydrogen bridges (stabilizing theparallel chains) are present in the direction of the a-axis while hydrophobic interactions exist in the c-axis direction. The crystalline sections comprise anaverage of 60% of native cellulose. These sections
are interrupted by amorphous gel regions, whichcan become crystalline when moisture is removed.The acid- or alkali-labile bonds also apparentlyoccur in these regions.
STRUCTURE
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STRUCTURE
The chains are probably somewhat pleated toallow intrachain hydrogen bridge formationbetween O-4 and O-6, and between O-3 and O-5.
Mi t lli C ll l
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Microcrystalline Cellulose
is formed when these bonds are
hydrolyzed. This partially depolymerized
cellulose product with a molecular
weight of 3050 kdal, is still water
insoluble, but does not have a fibrose
structure.
Unit cell of cellulose
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Unit cell of cellulose
(according toMeyerand Misch)
PROPERTIES
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PROPERTIES
has a variable degree ofpolymerization (denoted as DP;number of glucose residues per
chain)depending on its origin.
has a high molecular weight andcrystalline structure
it is insoluble in water
has a poor or negligible swellingpower or ability to absorb water
UTILIZATION
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UTILIZATION
Microcrystalline cellulose
Is used in lo-calorie food products andin salad dressings, desserts and ice
cream. Its hydration capacity and
dispersibility are substantiallyenhanced by adding it in combination
with small amounts of Carboxymethylcellulose.
CELLULOSE
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CELLULOSE
DERIVATIVES
Cellulose can be alkylated into a
number of derivatives with goodswelling properties and improved
solubility. Such derivatives have a wide
field of application.
Alkyl Cellulose,
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Alkyl Cellulose,
Hydroxyalkyl Cellulose
The reaction of cellulose with methylchloride orpropylene oxide in the presence of a strong alkaliintroduces methyl or hydroxypropyl groups into
cellulose. The degree of substitution (DS) isdependent on reaction conditions.
Mixed substituted products are also produced, e. g.,
methylhydroxypropyl cellulose or methylethylcellulose. The substituents interfere with the normalcrystalline packing of the cellulose chains, thusfacilitating chain solvation.
Continuation :
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Depending on the nature of the substituent (methyl, ethyl,
hydroxymethyl, hydroxyethyl or hydroxypropyl) and thesubstitution degree, products are obtained with variable
swelling powers and water solubilities.
A characteristic property for methyl cellulose and double-derivatized methylhydroxypropyl cellulose is their initial
viscosity drop with rising temperature, setting to a gel at a
specific temperature.
The above properties of cellulose derivatives permit their
diversified application
Continuation :
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In baked products obtained from gluten-poor or gluten-free
flours, such as those of rice, corn or rye, the presence ofmethyl and methylhydroxypropyl celluloses decreases the
crumbliness and friability of the product, enables a larger
volume of water to be worked into the dough and, thus,
improves the extent of starch swelling during oven baking.
Since differently substituted celluloses offer a large choice of
gelling temperatures, each application can be met using the
most suitable derivative.
Their addition to batter or a coating mix for meats (panure)
decreases oil uptake in frying.
Continuation :
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Their addition to dehydrated fruits and vegetables
improves rehydration characteristics and texture uponreconstitution.
Sensitive foods can be preserved by applying alkylcellulose as a protective coating or film.
Cellulose derivatives can also be used as thickeningagents in low calorie diet foods.
Hydroxypropyl cellulose is a powerful emulsionstabilizer, while methylethyl cellulose has the propertyof a whipping cream: it can be whipped into a stablefoam consistency.
Utilization of Cellulose Derivatives
(in amounts of 0 01 to 0 8%)
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(in amounts of 0.01 to 0.8%)
Carboxymethyl Cellulose
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Carboxymethyl Cellulose
Carboxymethyl cellulose is obtained bytreating alkaline cellulose with chloroaceticacid.
Carboxymethyl cellulose is an inert bindingand thickening agent used to adjust orimprove the texture of many food products,
such as jellies, paste fillings, spreadableprocess cheeses, salad dressings and cakefillings and icings.
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It retards ice crystal formation in ice cream, stabilizing the
smooth and soft texture.
It retards undesired saccharose crystallization in candy
manufacturing and inhibits starch retrogradation or the
undesired staling in baked goods.
Lastly, Carboxymethyl cellulose improves the stability and
rehydration characteristics of many dehydrated foodproducts.
HEMICELLULOSES
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HEMICELLULOSES
refers to substances which occupy thespaces between the cellulose fribils
within the cell walls of plants.
Various studies, e. g., on apples, potatoes, and
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, g , pp , p ,beans, show that xyloglucans dominate in theclass Dicotyledoneae.
In the class Monocotyledoneae, the
composition of the hemicelluloses in the
endosperm tissue varies greatly, e. g., wheatand rye contain mainly arabinoxylans, while -
glucans predominate in barley and oats.