C4. Other polysacs Flashcards
Cellulose:
- polymer of __________ units linked by __________ linkages
- digestible by humans?
- branches?
- present as __________ bundles which have extensive amounts of __________ regions –> highly organized by __________ bonding
- D-glucose units linked by b-1,4 glycosidic linkage
- humans don’t have enzymes to hydrolyze b-1,4 glycosidic linkage, making cellulose indigestible
- no branched counterpart –> only in linear form
- fiberlike bundles with crystalline regions –> by hydrogen bonding
cellulose often accompanied by other carbs (3) to form __________ components of most __________ tissues
- durable?
- hydrolysis of cellulose successful?
- hemicelluloses, pectic substances and lignin
- structural components of most plant tissues
- very durable! think of stability of paper + time it takes for wood to rot
- no one successfully applied cellulose hydrolysis commercially for production of glucose –> even acid hydrolysis is difficult to perform
the fact that cellulose is ___-_______ in nature can be turned to advantage for ___-_______ products
- by controlled hydrolysis, the more __________ regions of cellulose can be hydrolyzed, leaving behind __________ cellulose
- non-nutritive –> low-calorie products
- more amorphous regions (no defined form) –> microcrystalline cellulose
microcrystalline cellulose can be used as a __________ agent without contributing __________ + used extensively as a __________ agent (ie convert liquid products (honey, syrup) into ___-_______ __________ by absorption
- bulking agent without contributing calories
- plating agent –> convert liquid products into free-flowing powders by absorption
what is carboxymethyl cellulose (CMC)?
- 2 reaction equation?
- net result?
- methylated derivative of pure cellulose formed by hydrating cellulose in a strongly basic solution and then reacting it with sodium chloroacetate –> net result add a carboxymethyl group onto the chain
- R-OH + NaOH –> R-O^-Na+ + H2O
- R-O^-Na + sodium chloroacetate
Carboxymethyl cellulose –> a insoluble/soluble polymer that is capable of contributing ____________ to a solution as well as forming ______ ______
- soluble
- viscosity
- weak gels
presence of ____________ groups means that CMC is susceptible to ____ changes and may __________ out of solution around its ____________ points
- carboxyl groups
- pH
- precipitate out
- isoelectric point
if pH is above pka of carboxyl groups, CMC polymers attract/repel each other
repel
presence of ionized carboxyl groups allows _______ ______ to be used to cross-link the polymers to form a ________
- CMC has found wide application in food industry as a __________-enhancing agents that does not contribute any __________
- major application? where is provides (2)
- divalent ions
- gel
- viscosity
- any calories
- ice cream where it provides smooth texture and inhibits ice crystal growth during storage
cellulose derivatives other than CMC (2)?
- soluble or insoluble?
- viscosities affected by pH? why or why not?
- hydroxypropyl cellulose
- methyl cellulose
- quite soluble
- viscosities not affected by pH or salts since derivatives are non-ionic
Pectic substances
- are polysacs associated with _______ ________ btw _______ ________ ________ –> act as a ________ to hold cells together
- complex carb largely made up of _______________ acid = basic unit –> what groups may be esterified with other groups OR may be present as ______ ________ or its ________
- properties of pectic substances depend on their ________
- middle lammella btw plant cell walls
- act as a binder
- polygalaturonic acid –> carboxyl groups may be esterified with methyl groups OR present as free acid or its salt
- source
3 categories of pectic substances?
- pectic acids: polymers of predominantly polygalacturonic acid free of methyl ester groups
- pectinic acids: polymers of polygalacturonic acid with some degree of methylation (low methoxy pectin)
- pectin: polymers of polygalacturonic acid with >50% of carboxyl groups methylated
what has a major influence on pectic substances’ functional properties?
- this major influence depends on (2)
- degree of methylation!
- depends on source and on method of extraction
what is the major use of pectin?
- use sugar to prevent what?
production of jams and jellies
- use sugar to prevent microbial growth by reducing water activity?
in order for pectin to form a suitable gel, 3 components must be present + pH in range of ___-___
- sugar + acid + water
- 2.8-3.2
pectic substances:
- under low pH, attractive/repulsive charge of residual ________ groups is oxidized/reduced, while sugar competes for ________ of ________ –> allows polymers to associate in 3D manner forming a _____
- repulsive charge
- carboxyl group is reduced
- water of hydration
- gel
can pectin form a gel without sugar?
yes but large amounts are required = not economical
pectin mostly obtain as by-product of which industry?
- how is pectin extracted?
- what is important and determines quality and price?
- citrus industry –> orange/grapefruit peels
- extracted using dilute acid
- degree of methylation!
degree of methylation (DM)
- jellies: ?
- jams: ?
- jellies: DM around 50
- jams: contain particulate matter, rapid-setting pectin –> DM > 74 is required
what is used for diet jams and jellies?
- how are they produced? (2 ish)
- how to reduce the need for sugar
- low-methoxy pectin
- produced by controlled hydrolysis of methyl groups using either alkaline conditions or using enzyme pectin methyl esterase
- gel produced using divalent ions to cross-link polymers at carboxyl groups –> no sugar required + pH range is much broader
for diet products to be shelf-stable, what is added to compensate for the __________ effect (water activity reduction/increase) that is lost when __________ is not used in the product
- antimicrobial agents
- compensate for osmotic effect (water activity reduction)
- when sugar is not in the product
what are gums?
- 2 examples?
- both of these gums are __________, polymers of __________ and __________ consisting of __________ backbone with __________ side groups
- linkages?
- unique polysacs contained in seeds of some plants
- guar gum and locust bean gum
- galactomannans –> polymers of galactose and mannose
- mannose backbone (b-1,4 linkages) with galactose side groups (attached to mannose by a-1,6 linkages
Guar gum
- ratio of mannose to galactose?
- linear chain of __________ (_____ linkages) with __________ branches (_____ linkages) dispersed roughly every __________ mannose unit
- 2 mannose + 1 galactose
- D-mannose (b-1,4 linkages) with D-galactose branches (a-1,6 linkages) interspersed roughly every other mannose unit
most important property of guar gum? (2)
- particularly useful in assisting in __________ of dry powders used in __________ products (ie?)
- hydrate very rapidly in cold water
- form a very viscous solution
- rehydration used in instant products (ie instant soup)
Locust bean gum
- in this galactomannan, ratio of mannose to galactose? –> branch of mannose/galactose every ______ or ________ mannose/galactose unit
- similar to guar gum, except that it requires what?
- used extensively in ______ __________ to impart a smooth meltdown and freeze/thaw __________
- also used in __________ industry to produce ______ doughs
- 4:1 or 5:1 –> branch of galactose every fourth of fifth mannose unit
- requires more heating to go into solution
- ice cream
- freeze/thaw resistance
- baking industry to produce softer doughs
3 general properties of guar gum and locust bean gum?
- viscosity does not change much with pH
- stability and rheology are not affected much by processing
- these gums are compatible with starches, cellulose and other gums
how are plant exudate gums obtained?
- 4 main plant exudate gums?
- these gums are all __________ ______polysacs –> due to presence of __________ acid
- ex.: gum arabic is a __________ consisting of (4)
- by wounding specific tropical trees and shrubs and collecting the exudate (just like maple syrup)
- arabic, ghatti, karaya and tragacanth
- charged heteropolysaccharides –> due to presence of glucuronic acid
- polysaccharide consisting of D-galactose, L-arabinose, L-rhamnose and D-glucuronic acid
- distinguishing feature of gum arabic is that it is extremely soluble/insoluble in water –> can make up to ____% solutions
- major use of gum arabic is as a _______ __________/__________
- commonly used to convert citrus essential oil flavor __________ to a water-dispersible __________ by _______ drying
- also used extensively to inhibit sugar __________ and as a __________ in candies, jellies and chewing gyms
- soluble in water –> 50% solutions
- flavor carrier/dispersant
- emulsions to water-dispersible powder by spray trying
- crystallization and as a thickerner
3 polysacs extracted from seaweeds
- irish moss: carrageenan
- red algae: agar
- giant kelp (brown algae): alginates
carrageenan:
- polysac composed of ____A______ and __________ units with some _____A_____ moieties being __________
- linear and/or branched?
- has unique ability to complex with ______ proteins to form a _____ –> hence used extensively in (2)
- D and L-galactose and 3,6 anhydro-D-galactose units with some galactose moieties being sulfonated
- made up of 2 fractions: linear and branched
- milk proteins to form a very light gel
- used extensively to suspend insoluble chocolate solids in chocolate milk + in ice cream to minimize drip
agar
- similar to __________ in composition but derived from ____ __________
- unique ability to form a _________ ____ that sets at about ___°C
- best known for its used in ______________ media
- used as a __________ agent for (4)
- carrageenan but derived from red algae
- thermoreversible gel that sets at 40°C
- bacteriological media
- gelling agent –> bakery products, confections, meat and fish products
alginates
- polysacs obtained from _______ __________ (giant _____)
- made up of largely linear/branched polymers of __________ and __________
- presence of __________ groups makes alginates sensitive to ____ and _______ __________ of food system
- extracted in what form so that they will be readily ________
- similarly to behavior of carboxy-methyl cellulose and low methoxy pectin, gels can be produced by _____-__________ using __________ _____ such as __________
- brown algae (giant kelp)
- linear polymers of D-mannyronic and L-glucuronic acids
- carboxylic groups –> pH and ionic strength
- sodium salts –> readily soluble
- cross-linking using divalent ions such as calcium
many microorgs produce __________ which are _______________ polysaccharides
- slimes
- extracellular polysaccharides
dextrans
- are polysacs made up of __________ that differ from starch bc linked together via what? with what branch points?
- form organized crystalline granules?
- glucose
- linked by a-1,6 linkages with a-1,3 linkages at branch points
- do NOT form organized crystalline granules
leuconostoc mesenteroides is the most common organism used to produce __________ by fermentation of __________
- dextran
- fermentation of sucrose
xanthan gum:
- unique __________ gum that has made major inroads into food industry
- complex ______ polysac made up of (3) present in what ratio?
- __________ __________ can produce xanthan gum from what?
- microbial
- heteropolysaccharide made up of D-glucose, D-mannose and D-galacturonic acid
- 3:3:2 ratio
- xanthmonous campestris
- from variety of cheap carbohydrates substrates
4 major properties of xanthan gum
- very useful in production of (2) without need for __________
- excellent heat stability: almost no change in viscosity with change in temp
- viscosity is highly affected by shear, but returns immediately after shear is removed (pseudoplastic)
- viscosity is practically independent of pH, very useful in highly acidic foods
- will form a gel with locust bean gym in very low concentrations
- instant puddings or gels without need for heat
like all naturally sourced polymeric molecules, base polysaccharides can be ____________ to further modify their ___________
- derivatized
- properties
