C4. Other polysacs
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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)