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Food Chemistry 1 > C3. Starch > Flashcards

C3. Starch Flashcards

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1
Q

3 common polysacs?
+ 4 types of gums

A

starch + cellulose + pectins
others:
- seed gums: guar gum, locust bean gum
- plant exudate gums: gum arabic, gum tragacanth
- seaweed gums: agar, carrageenan
- microbial gums: dextran, xantham gum

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2
Q

properties of polysacs are a function of (4)

A
  1. sugar/chemical makeup
  2. presence of unique functional groups
  3. molecular weight and degree of branching
  4. combination thereof
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3
Q

are proteins or carbs more complex?

A

proteins! bc less variation in base units of carbs that make up the polymer

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4
Q

2 most abundant form of stored carb available on earth?

A

starch and cellulose
- starch = energy store for seed germination

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5
Q

starch
- main source of ________ ________ (4 ex)
- large quantities isolated from ______ sources and used as functional ingredient in food industry due to 2 properties

A
  • dietary carbohydrates (potatoes, rice, corn, wheat)
  • plant sources
  • thickening/texture-modifying agent + source of sugars and dextrins
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6
Q

starch
- made up exclusively of __-__________
- made up of 2 fractions + describe (shape + linkage)

A
  • D-glucose
    1. amylose: long chain linear polymer composed of D-glucose linked by a-1,4 glycosidic bonds
    2. amylopectin: branched polymer composed of D-glucose linked by a-1,4 glucosidic bonds in its linear portion and a-1,6 bonds at its branch points
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7
Q

starch is found in most plant sources as ______ water- soluble/insoluble granules

A

hard water-insoluble granules

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8
Q

each starch source contains ________ and _________ in genetically predetermined ________
ie: corn starch? vs waxy maize

A
  • amylose and amylopectin in genetically predetermined ratios
  • corn starch: 28% amylose + 62% amylopectin
  • waxy maize: 100% amylopectin
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9
Q

starch is readily isolated from plant source by ____ _______, then ________ out of solution and _______
- produces _____ _______ powder composed of ________ starch granules
- each granule is made up of _________ amylose and amylopectin tightly bound and held together by __________ between the polymers

A
  • wet milling + centrifuged out + dried
  • dry white powder
  • anhydrous amylose and amylopectin
  • H-bonds
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10
Q

what leads to starch gelatinization?
- process of gelatinization (5 steps)

A

heating in presence of moisture breaks the H-bonds = gelatinization
1. gradual swelling of the granule due to absorption of water facilitated by heat
2. increasing kinetic energy breaks H-bonds
3. granule slowly hydrates as water molecules access OH groups on the polymer
4. as kinetic energy is reduced, random H-bonds reform –> extensively H-bonded starch molecules trap water within matrix formed, producing a gel

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11
Q

at what temp does loss of granular integrity general occurs?
- gelatinization temperature is a function of the starch ________

A
  • 60-70°C
  • stach source
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12
Q

gelatinization:
- when granules have swollen extensively, viscosity of solution increases/decreases drastically, causing ________
- if solution is stirred, granules break up and ________ to form a ________ solution

A
  • increases causing pasting
  • disperse
  • colloidal solution
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13
Q

gelatinization:
- if concentration of starch is high –> forms what? upon cooling
- if concentration of starch is low –> forms what upon cooling?

A
  • high starch = gel upon cooling
  • low starch = obtain a viscous solution that does not form a gel
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14
Q

gelatinization of starch occurs as function of 5 variables

A
  1. concentration of starch
  2. amylose:amylopctin ratio of starch
  3. average molecular weight (chain length) of starch
  4. rate of cooling
  5. presence of other components in solution (salt, sugar, fat)
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15
Q

amylose:
- linear polymer with what structure?
- solubility? why?
- functionally useful?

A
  • long thin helical filament-like structure
  • very low solubility bc readily hydrogen bonds to neighboring polymers to form large aggregates that precipitate out of solution
  • on its own, useless functionally in food systems bc insoluble
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16
Q

amylopectin:
- structure?
- soluble in water?
- forms a _________ solution –> branching produces what in solution
- in presence of amylose which acts as a _____-_________ agent, a _____ can form, _________ water

A
  • highly branched water dispersible macromolecule
  • yes!
  • forms a viscous solution
  • branching produces a tangled net-like web in solution
  • amylose = cross-linking agent –> 3D gel can form, entrapping water
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17
Q

what is retrogradation?
- happens when?

A
  • when starch gels become firmer with time –> generally undesirable
  • due to continued hydrogen bond formation between starch molecules
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18
Q

what 2 problems arise with retrogradation?

A
  1. texture of gel changes over time, which is generally undesirable
  2. syneresis (exudation of water) may occur, where gel tightens up so much that it starts to exude water
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19
Q
  • retrogradation causes color change?
  • retrogradation is one of key processes responsible for (2)
A
  • causes starch gels to become more opaque with time
  • staling of bread + stiffening of pie filling
    (when you expose starch to air
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20
Q

normal corn starch vs waxy maize starch vs potato and tapioca starch
- which will form a gel?
- why?

A
  • normal corn starch (28% amylose) –> set to a rigid opaque gel
  • waxy maize starch (100% amylopectin) –> NOT form a gel
  • potato and tapioca starch (23-28% amylose) form reasonable stable gels that tend to maintain their clarity and do not stiffen appreciably with time attributed to their high average molecular weight = less mobile –> H-bonds continue to develop btw them over time but at a much slower rate
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21
Q

sugars tend to accelerate/retard gel formation and retrogradation
why?

A

retard!
- they compete for available water and interfere with starch to starch hydrogen bonding

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22
Q

surface-active agents (surfactants and emulsifiers) tend to activate/inhibit retrogradation and gelation –> forming what?

A

inhibit
- form complexes with starch, most noticeable with high-amylose starch systems

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23
Q

pH of most foods lies in range of __-___
- affects behaviour of starches? why?
- vs highly acidic food + heat –> possibility of what?

A

4-7
- nope because natural starches are uncharged
- of reduction of viscosity due to hydrolysis of starch

24
Q

does ionic strength have effect on most starches?

A

only minor effects bc most starches have no ionizable groups –> change in ionic strength has little influence relative to its effects on a macromolecules such as protein which may be extensively charged

25
Q

effect of protein on starch in terms of ________ and _______
- effect of starch on ______ proteins is well known –> produce what?

A

proteins are capable of dramatically changing how a starch behaves in terms of gelation and viscosity (+ texture)
- milk –> pudding (smooth gel)

26
Q

in North America, most of our starch is derived from what?
- starch used in native state? why or why not?

A

corn
- rarely used except in home applications –> modify starch to produce specific properties that are desired by food processor

27
Q

pre-gelatinized starch:
- starch granules are heated above/below gelatinization temp –> causing them to _________, and are then ____-_____
- causes some _________ in starch granule, making it _________ in cold water + requires more/less heat or time to develop viscosity
- inconvenience?

A
  • below –> swell –> drum-dried
  • disorganization of starch granule –> dispersible in cold water
  • requires less heat
  • inconvenience: higher amount of pre-gelatinized starch is required to attain similar viscosity effects as with untreated starch
28
Q

acid-modified starch
- produced by holding starch just below/above its gelatinization temp in an ________ medium –> then ____________ and ___________
- acid is used to partially and _________ly ____________ the ____________ linkages in starch granule without breaking up integrity of granule per say
- ______-________ starches are used in candy manufacture –> produce what?

A
  • below in acidic medium
  • then neutralized and dried
  • randomly hydrolyzes glycosidic linkages in starch granules
  • thin-boiling starches –> produce easy-to-handle low-viscosity fluids that can be poured into molds and will set into a firm gel upon cooling –> forming starch gum candies (jujubes)
29
Q

cross-linked starches:
- used when what is desired?
- how is that reached? (2) –> however, they normally ______ down
- solution?
- typically what (3) are used as cross-linking agents? can do what?

A
  • maximum viscosity or pasting of starch is desired
  • max viscosity reached when granules are swollen extensively but still intact –> however, swollen granules normally break down with subsequent shear
  • can hold granules together by cross-linking starch chemically so that swollen granule retains integrity
  • acetic, citric or adipic anhydrides are used as cross-linking agents –> can bridge 2 hydroxyls from adjoining polymers and hold swollen granule structure together
30
Q

result of cross-linked starch
- swell more/less?
- maintain integrity
- viscosity level?
- resistant to shear?
- susceptible to acid hydrolysis?

A
  • swell somewhat less but maintain integrity
  • maximum viscosity somewhat lowered BUT much more resistant to shear
  • less susceptible to acid hydrolysis as cross-links make up for some of the bonds broken by actions of acid
31
Q

starch derivatives are used to (3)
- Overall objective of starch derivatives?

A
  1. control retrogradation and staling
  2. improve freeze/thaw stability
  3. reduce textural and opacity changes
    - reduce polymer-polymer hydrogen bonding via steric hindrance or introduction of charged groups (to keep polymers from reforming H-bonds)
32
Q

what charged groups are added to starch?
- like-charged polymers ______ –> decreasing/increasing stability against retrogradation

A

orthophosphate groups (are charged except at low pH)
- repel!
- increasing stability against retrogradation

33
Q

use of ______ _________ (NaOCl) to ____A______ a portion of hydroxyl groups to __________ groups (some __________ and __________ groups may also be introduced)

A
  • sodium hypochlorite (NaOCl) to oxidize
  • hydroxyl to carboxyl groups
  • some aldehyde and ketone
34
Q

oxidized starches become __________ –> thereby stabilized against __________ but more susceptible to variations in ____ and _______ __________ in food product
- solubility becomes _____ dependant

A
  • charged
  • against retrogradation
  • pH and ionic strength
  • pH dependant
35
Q

2 basic types of starch conversions? name + produces what?

A
  1. dry pyroconversion: for production of cold-water soluble starches
  2. acid hydrolysis: wet conversion for production of dextrins or as a preliminary step in production of sugars from starch
36
Q

pyroconversion:
- starch granules are sprayed with dilute ____ and subjected to relatively low/high temps
- 4 reactions may take place

A
  • HCl + high temps
    1. hydrolysis of a-1-4 and a-1-6 linkages
    2. transglucosidation: breaking of 1-4 linkages and formation of other linkages, generally random in nature (1,3 or 1,5 linkages)
    3. repolymerization: any free sugars produced can repolymerize
    4. caramelization: free sugars can undergo caramelization reaction
37
Q

3 basic products can be produced by pyroconversion
- name
- under what conditions (high/moderate/low moisture, acid, temp)
- color?
- soluble in water?

A
  1. white dextrins:
    - high moisture, high acid, low temp
    - hydrolysis predominates –> can be controlled to produce desired ranges of viscosity
    - soluble in cold water
  2. yellow dextrins:
    - lower moisture, moderate acid, higher temp
    - color due to non enzymatic browning reaction (caramelization)
    - viscosity and degree of polymerization can be controlled
  3. british gums:
    - little to no acid used –> higher temps
    - dark in color with little hydrolysis + much more transglucosidation
    - product is much more viscous and capable of forming a stiff gel –> used extensively in candy manufacture
38
Q

acid/enzymatic hydrolysis of starch:
- half of isolated starch produced is converted to __________ and __________
- old means vs today?
- starch is gelatinized in presence of __________ acid and __________ _____

A
  • syrups and sugars
  • old means: only acid hydrolysis VS today: acid hydrolysis = common preliminary step to make it lower MW (in conversion of starch to syrups/sugars)
  • hydrochloric acid + pressurized steam
39
Q

acid/enzymatic hydrolysis of starch (into syrups/sugars):
- hydrolysis is __________ and __________ –> producing (2)
- starch breakdown can be followed by measuring ________ ______ content of hydrolysate

A
  • random and extensive
  • produce dextrins (low molecular weight starch) and sugars
  • reducing sugar content
40
Q

as hydrolysis increases and mono, di and oligosacs are produced, reducing sugar content increases/decreases

A

increases!

41
Q

reducing sugar content is expressed in terms of what (A)?
- (A) is the ratio of what?
- if hydrolysis of starch is 100% complete, then (A) = ?

A
  • dextrose equivalents (DE)
  • ratio of reducing power (RP/g of syrup) relative to (RP/g of dextrose (D-glucose)) * 100
  • DE = 100
42
Q

acid hydrolysis cannot yield dextrose equivalents much beyond _____ since equilibrium is reached btw __________ and __________

A
  • 50
  • hydrolysis and repolymerization
43
Q

what is the best way to produce very sweet, high DE syrups? vs what?

A

enzymatic convertion of gelatinized starch!
- not acid hydrolysis (low DE)

44
Q

4 enzymes that do enzymatic conversion + basic role
- together, convert what to what?
- net result: DE > ?

A
  1. a-amylase: reduce MW
  2. b-amylase: produces maltose
  3. glucoamylases: converts maltose to glucose
  4. pullalanase: takes care of branch points
    - convert starch to predominantly D-glucose (dextrose)
    - DE > 90
45
Q

a-amylase
- endo/exo enzyme?
- attacks where?
- known as __________ enzyme. why?
- random _______ bond breakage increases/reduces overall MW of starch
- end products (4)

A
  • endoenzyme
  • attacks anywhere within starch molecule other than the a-1,6 branch point
  • liquefying enzyme –> causes viscosity of starch solution to drop rapidly
  • random internal bond breakage reduces MQ
  • mainly oligosacs + some glucose, maltose and pannose (trisac containing a-1,6 linkage)
46
Q

b-amylase:
- endo/exoenzyme?
- attacks where?
- produces what? how?
- known as ______ enzyme as it develops __________ rapidly but __________ does not change significantly

A
  • exoenzyme
  • attacks non-reducing end of the starch chain
  • produces maltose by hydrolyzing a-1,4 glycosidic bond every 2 glucose units over
  • saccharifying enzyme as it develops sweetness rapidly but viscosity doesn’t change
47
Q

glucoamylases:
- capable of removing single __________ units from __________ end of starch and split __________ into what?
- combined action of a and b-amylase + glucoamylase leaves __________ __________ –> largely what?

A
  • glucose units from non-reducing end of starch and split maltose into 2 glucose units
  • limit dextrins –> largely the trisaccharide pannose
48
Q

pullulanase
- hydrolyzes which linkages?
- attacks what?

A
  • a-1,6 glycosidic linkages
  • attacks branch points so that trisaccharide pannose can be broken down to glucose plus maltose
49
Q

at DE > 90, glucose can be __________ out of solution and obtained in ______ form in manner very similar to __________ refining
- glucose is a useful sweetener but as sweet as sucrose?

A
  • crystallized
  • pure form
  • sucrose refining
  • glucose = not as sweet as sucrose
50
Q

what enzyme converts D-glucose to D-fructose? how much %?
- D-fructose sweeter than glucose? vs sucrose?

A
  • glucose isomerase, 45%
  • D-fructose 1.3 times sweeter than glucose + somewhat sweeter than sucrose
51
Q

high fructose corn syrups are similar to ________ _______ and are in direct competition with _________, which is commonly __________ (using enzyme ________) to stabilize its sweetness in acidic environments

A
  • invert syrups
  • sucrose
  • inverted
  • enzyme invertase
52
Q

why is sucrose inverted?

A

glycosidic link in sucrose is acid labile and readily hydrolyzed by heat or acid –> for acidic beverages, sweetness can be stabilized by inversion

53
Q

the term inverted refers to the change in specific rotation of plane-polarized light by a sucrose solution –> converted to a mixture of (3)
- in a fully converted solution, direction of rotation is inverted (from 66.5° to _____ in the solution of (3 mixture) generated by rxn of sucrose with invertase enzyme

A
  • sucrose, glucose and fructose
  • 66.5 to -39° in solution of sucrose, glucose and fructose
54
Q

why does high-fructose syrup has great value? (3)

A
  1. intrinsically sweeter than glucose, becomes sweeter with decreasing temp
  2. more soluble
  3. does not crystallize readily bc it is a mixture of sugars (good for frozen products)
55
Q

RECAP
- starch is mainly used for its __________-modifying properties and for production of __________/__________
- in acidic foods, _____-_____ starches are used to minimize __________ during heat treatment
- starches are extensively modified to prevent __________ in systems where action is detrimental (ie __________ foods)

A
  • texture-modifying properties
  • production of syrups/sweeteners
  • cross-linked starches –> minimize hydrolysis
  • retrogradation (frozen foods)
56
Q
A

Food Chemistry 1 (22 decks)

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