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)
