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Food Chemistry 1 > C4. Other polysacs > Flashcards

C4. Other polysacs Flashcards

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1
Q

Cellulose:
- polymer of __________ units linked by __________ linkages
- digestible by humans?
- branches?
- present as __________ bundles which have extensive amounts of __________ regions –> highly organized by __________ bonding

A
  • 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
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2
Q

cellulose often accompanied by other carbs (3) to form __________ components of most __________ tissues
- durable?
- hydrolysis of cellulose successful?

A
  • 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
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3
Q

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

A
  • non-nutritive –> low-calorie products
  • more amorphous regions (no defined form) –> microcrystalline cellulose
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4
Q

microcrystalline cellulose can be used as a __________ agent without contributing __________ + used extensively as a __________ agent (ie convert liquid products (honey, syrup) into ___-_______ __________ by absorption

A
  • bulking agent without contributing calories
  • plating agent –> convert liquid products into free-flowing powders by absorption
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5
Q

what is carboxymethyl cellulose (CMC)?
- 2 reaction equation?
- net result?

A
  • 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
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6
Q

Carboxymethyl cellulose –> a insoluble/soluble polymer that is capable of contributing ____________ to a solution as well as forming ______ ______

A
  • soluble
  • viscosity
  • weak gels
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7
Q

presence of ____________ groups means that CMC is susceptible to ____ changes and may __________ out of solution around its ____________ points

A
  • carboxyl groups
  • pH
  • precipitate out
  • isoelectric point
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8
Q

if pH is above pka of carboxyl groups, CMC polymers attract/repel each other

A

repel

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9
Q

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)

A
  • divalent ions
  • gel
  • viscosity
  • any calories
  • ice cream where it provides smooth texture and inhibits ice crystal growth during storage
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10
Q

cellulose derivatives other than CMC (2)?
- soluble or insoluble?
- viscosities affected by pH? why or why not?

A
  • hydroxypropyl cellulose
  • methyl cellulose
  • quite soluble
  • viscosities not affected by pH or salts since derivatives are non-ionic
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11
Q

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 ________

A
  • 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
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12
Q

3 categories of pectic substances?

A
  1. pectic acids: polymers of predominantly polygalacturonic acid free of methyl ester groups
  2. pectinic acids: polymers of polygalacturonic acid with some degree of methylation (low methoxy pectin)
  3. pectin: polymers of polygalacturonic acid with >50% of carboxyl groups methylated
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13
Q

what has a major influence on pectic substances’ functional properties?
- this major influence depends on (2)

A
  • degree of methylation!
  • depends on source and on method of extraction
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14
Q

what is the major use of pectin?
- use sugar to prevent what?

A

production of jams and jellies
- use sugar to prevent microbial growth by reducing water activity?

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15
Q

in order for pectin to form a suitable gel, 3 components must be present + pH in range of ___-___

A
  • sugar + acid + water
  • 2.8-3.2
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16
Q

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 _____

A
  • repulsive charge
  • carboxyl group is reduced
  • water of hydration
  • gel
17
Q

can pectin form a gel without sugar?

A

yes but large amounts are required = not economical

18
Q

pectin mostly obtain as by-product of which industry?
- how is pectin extracted?
- what is important and determines quality and price?

A
  • citrus industry –> orange/grapefruit peels
  • extracted using dilute acid
  • degree of methylation!
19
Q

degree of methylation (DM)
- jellies: ?
- jams: ?

A
  • jellies: DM around 50
  • jams: contain particulate matter, rapid-setting pectin –> DM > 74 is required
20
Q

what is used for diet jams and jellies?
- how are they produced? (2 ish)
- how to reduce the need for sugar

A
  • 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
21
Q

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

A
  • antimicrobial agents
  • compensate for osmotic effect (water activity reduction)
  • when sugar is not in the product
22
Q

what are gums?
- 2 examples?
- both of these gums are __________, polymers of __________ and __________ consisting of __________ backbone with __________ side groups
- linkages?

A
  • 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
23
Q

Guar gum
- ratio of mannose to galactose?
- linear chain of __________ (_____ linkages) with __________ branches (_____ linkages) dispersed roughly every __________ mannose unit

A
  • 2 mannose + 1 galactose
  • D-mannose (b-1,4 linkages) with D-galactose branches (a-1,6 linkages) interspersed roughly every other mannose unit
24
Q

most important property of guar gum? (2)
- particularly useful in assisting in __________ of dry powders used in __________ products (ie?)

A
  • hydrate very rapidly in cold water
  • form a very viscous solution
  • rehydration used in instant products (ie instant soup)
25
Q

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

A
  • 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
26
Q

3 general properties of guar gum and locust bean gum?

A
  1. viscosity does not change much with pH
  2. stability and rheology are not affected much by processing
  3. these gums are compatible with starches, cellulose and other gums
27
Q

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)

A
  • 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
28
Q
  • 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
A
  • soluble in water –> 50% solutions
  • flavor carrier/dispersant
  • emulsions to water-dispersible powder by spray trying
  • crystallization and as a thickerner
29
Q

3 polysacs extracted from seaweeds

A
  1. irish moss: carrageenan
  2. red algae: agar
  3. giant kelp (brown algae): alginates
30
Q

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)

A
  • 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
31
Q

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)

A
  • carrageenan but derived from red algae
  • thermoreversible gel that sets at 40°C
  • bacteriological media
  • gelling agent –> bakery products, confections, meat and fish products
32
Q

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 __________

A
  • 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
33
Q

many microorgs produce __________ which are _______________ polysaccharides

A
  • slimes
  • extracellular polysaccharides
34
Q

dextrans
- are polysacs made up of __________ that differ from starch bc linked together via what? with what branch points?
- form organized crystalline granules?

A
  • glucose
  • linked by a-1,6 linkages with a-1,3 linkages at branch points
  • do NOT form organized crystalline granules
35
Q

leuconostoc mesenteroides is the most common organism used to produce __________ by fermentation of __________

A
  • dextran
  • fermentation of sucrose
36
Q

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?

A
  • 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
37
Q

4 major properties of xanthan gum
- very useful in production of (2) without need for __________

A
  1. excellent heat stability: almost no change in viscosity with change in temp
  2. viscosity is highly affected by shear, but returns immediately after shear is removed (pseudoplastic)
  3. viscosity is practically independent of pH, very useful in highly acidic foods
  4. will form a gel with locust bean gym in very low concentrations
    - instant puddings or gels without need for heat
38
Q

like all naturally sourced polymeric molecules, base polysaccharides can be ____________ to further modify their ___________

A
  • derivatized
  • properties

Food Chemistry 1 (22 decks)

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