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Food Structuring > Polysaccharide > Flashcards

Polysaccharide Flashcards

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1
Q

What type of equipment we use to study molecular weight distribution of a polymer?

A

HPSEC. high performance size exclusion chromatography

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2
Q

When would we use HPSEC and what can we observe

A

We use HPSEC to study the effect of enzymatic hydrolysis as larger molecules are less retained in the column compared to smaller molecules.

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3
Q

Can we use GC or HPSEC for uronic acids?

A

No, only suitable for neutral sugars. Uronic acids could be analyzed with HPAEC.

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4
Q

How can one analyze degree of methylation, acetylation and amidation?

A

Methylation: by GC or spectrophotometric colour assay.
Acetylation: by enzymatic colour assay using spectrometry or by HPLC or GC.
Amidation: complex, e.g. for pectin, as no nitrogen present, if nitrogen present then corresponds to level of amide groups.

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5
Q

How can one test for presence of anionic polysaccharides?

A

By complex formation with methylene blue. If color formation then it is an anionic polysaccharide. (partly) methyl esterfied pectin will not show a color reaction.

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6
Q

How can one differentiate between different carrageenan?

A

With a rhodizonate color assay and then using calibration curve compare it to reference sample.

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7
Q

Which are the three main enzyme that hydrolyze pectin and which pectin, high or low do they target?

A

PME -> remove methyl esters
PL -> cleaves glycosidic linkage between neighboring methyl esterified galA
PG -> cleave glycosidic linkage between neighboring non-methyl esterified galA
PME and PL target HM-pectin while PG LM-pectin.

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8
Q

What is the difference between locust bean gum and guar gum?

A

They are both galactomannans but differ in galactose subtitution. Locust bean gum has very low galactose substitution while guar gum has very high galactose substitution.

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9
Q

What is the name of the technique employed to distinguish between polysaccharide using enzymes with high specificity?

A

Enzymatic fingerprinting

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10
Q

Please provide origin of the following polysaccharides:
Pectin
Alginate
Carrageenan
Galactomannans
Starch
Xanthan Gum
Gum arabic
Cellulose

A

Pectin - middle lamella of lime, lemon and orange peel.
Alginate - brown seaweed
Carrageenan - red seaweed
Galactomannans - endosperm of different seeds
Starch - potato, wheat, cassava.
Xan gum- fermentation of glucose or sucrose by bacteria Xanthomonas capestris/or/phaseoli
Gum arabic - wounds in the bark of acacie tree specie
Cellulose - wood, flax or cotton fibre.

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11
Q

How can one extract HM pectin?

A

By having pectin suspended in methanol at low pH and temp <50C.

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12
Q

What are the three main regions in pectin?

A

Homopolygalacurnonan (HG) is the main region with galacturonic acid. The other two regions include RG I and RG II which can substituted with sugars.

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13
Q

How can one make amidated pectin and what are its advantages?

A

Adding ammonia to alcoholic suspension with pectin below <10C. Part of methyl are substituted with amide groups. The advantages are that gels can occur at lower pectin and calcium concentrations. At pH> 3.5 gel will have similar properties to LM pectin gel and be spreadable
At pH<3.5 gel will have similar properties to HM pectin gel and be firm.

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14
Q

What happens if pectin is left at neutrial/alkaline pH and ambient temperature (50C)?

A

Methyl and acetyl groups remved by alkaline pH. And galacturonic acid is broken down by B-elimination and decrease gelling power.

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15
Q

What is the pKa of pectin and of alginate?

A

3 and 3.6

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16
Q

LM pectin form egg box model with calcium. How does HM pectin instead form a gel.

A

Sugar acid gel. Addition of sugar which removed water making pectin molecules move close together. Lower pH, make pectin loose charge and become neutral further increasing interactions between chains. Gel is formed.

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17
Q

Is alginic acid soluble?

A

Alginic acid and calcium alginate are both insoluble. Sodium, potassium alginate and ammonium alginate are soluble and form viscous solutions.

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18
Q

Is it suitable to use sodium alginate for acidic products?

A

No, becuase it would be converted to alginic acid which is insoluble.

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19
Q

Is alginate susceptible to B-elimination?

A

No, because no ester groups are present which limit b -elimination

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20
Q

What are the two type of gels that can form with alginate?

A

Alginic acid gel upon acidification of sodium alginate. And gel with addition of calcium.

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21
Q

What are the properties of alginate gels?

A

Heat stable but shows syneresis upon storage.

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22
Q

How can we extract k-carrageenan?

A

With aid of potassium chloride. The rest are performed with alcohol.

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23
Q

Is carrageenan linear or branched?

A

Linear

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24
Q

Building blocks of alginate?

A

Guluronic and mannuronic acid.

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25
Q

What are the difference between k, iota, and lambda carrageenan.

A

K -> one sulphate group and galactose and anhydrogalactose residues
iota -> two sulphate groups and galactose and anhydrogalactose residues
lambda -> three sulphate groups and galactose and NO anhydrogalactose residues (only galactose).

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26
Q

What is the most soluble carrageenana?

A

Lambda as most hydrophilic due to more sulphate groups.

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27
Q

What is the solubility of carrageenan at high temp?

A

All carrageenan are soluble

28
Q

And in the presence of salts? How doe carragenna solubility differ?

A

K -> soluble with Na but not with potassium and calcium
iota -> soluble with Na and give thixotropic behaviour with calcium
lambda -> always soluble

29
Q

Why can lambda carrageenan not form a gel?

A

Becuase it does not posses anhydrogalactose unit which is essential to form a helical structure.

30
Q

What can happen to carrageenan at low pH?

A

Autohydrolysis of anhydrogalactose units especially at high temp and low cation level.

31
Q

How does K- carrageenan make a gel and describe properties of the gel.

A

Upon heat forms random coil and upon cooling helical structure form. Potassium ions decrease repulsion and faciliate interactions between chains. Potassium ions stabilize helical strucure. Gel is firm, brittle, give synersis upon storage and non stable against freeze thaw cycle.

32
Q

How does iota- carrageenan make a gel and describe properties of the gel.

A

Upon heat forms random coil and upon cooling helical structure form. Forms calcium brigdges between helical structures. Gel is elastic, cohesive, and stable against syneresis and freeze thaw cycle.

33
Q

How can carrageenan interact with proteins in milk?

A

At high pH, carrageenan and protein and negatively charge and will form calcium bridges. At low pH, carrageenan will interact with postive charge protein directly and stabilization and gelling occurs.

34
Q

How is the new gel formed between k-carrageenan and locust bean gum?

A

More elastic, greater water binding capacity and reduction in degree of syneresis.

35
Q

Galactomannans backbone?

A

Mannoses with galactose substitution at O-6.

36
Q

What is the mannose to galactose ratio for cassia gum, locust bean gum, tara gum, guar gum and fenugreek gum.

A

8:1, 4:1, 3:1, 2:1 and 1:1 respectively.

37
Q

How is solubility affected as more galactose units are present? and why galactomannan would tend to be insoluble.

A

They would tend to be insoluble because of their cellulosic like backbone. More galactose units present will lead to less interactions between chains and thus greater solubility.

38
Q

What happens to the viscosity of galactomannans when molecular weight decreases.

A

Molecular weight can decrease at high temp and low pH and this will cause viscosity to decrease.

39
Q

What is the interaction between xanthan and galactomannans?

A

Can increase viscoscity and have an interaction gel between the helical xanthan structure and the non substituted parts of locust bean gum. A gel can be created with max hardness achieved at 45% xan and 55% locust bean gum. More unsubstituted galactomanna better interaction. If mixed with gelling polysaccharide like agar and carrageenan gel stregnth can increase.

40
Q

Is native starch soluble or insolbule in water

A

Insoluble.

41
Q

What are the two type of components in starch granules?

A

Amylose, linear, and amylopectin which is branched.

42
Q

Why is waxy starch used to reduce retrogradation of starch?

A

Because of its low amount of amylose.

43
Q

How can starch be modified?

A

By physical, crosslinking and by stabilization by substitution.

44
Q

Are native starch gel stable against syneresis?

A

No

45
Q

Is the bacteria still present in xanthan gum?

A

No, after fermenation is killed and removed by centrifugation.

46
Q

Describe structure of xanthan gum.

A

Cellulose backbone with every one yes and one no glucan has side chain of trisaccharide composed of two mannose and a glucoronic acid. First mannose substituted with acetyl group and second mannose substituted with pyruvate or acetyl group.

47
Q

How can one influence transistional behaviour (disordered xanthan, not in helixes any more) of xanthan?

A
  1. Ionic strength -> more salt higher temperature needed for disorder (also higher Tm)
  2. pH
  3. amount of acetyl and pyruvate groups.
48
Q

How does xanthan gum viscosity change with increasing shear rate?

A

Decreases almost linearly. At no shear rate has very high viscosity and thus suitable for salad dressing as can keep particles suspended and during pouring viscosity decreases.

49
Q

Can xanthan form a gel?

A

No

50
Q

How can xanthan form a gel?

A

Ineraction with galactomannans such as locust bean gum or tara gum which produces transparent and thermo-reversible gels.

51
Q

Can xanthan gum form a gel with guar gum?

A

No, only increase viscosity.

52
Q

Gellan is made by which repeating units?

A

Glucose, glucoronic acid and rhamnose.

53
Q

How is the viscosity related to shear rate for gellan solutions? What is it its behaviour?

A

Shear thinning

54
Q

How do you obtain a gel with gellan and what factors influence its gelling?

A

Gel obtained by heating and cooling. Harder and more brittle gels obtained when gellan is less acetylated as it becomes more sensitive to calcium.

55
Q

Is gum arabic soluble? and xanthan?

A

Yes and yes

56
Q

Why is gum arabic a good emulsifier?

A

Becuase it has a protein part which allows it to stabilize oils as protein adheres to oil interface and carb extends outside. And thus suitable for encapsulation of flavors.

57
Q

Why is gum arabic suitable for confectionary?

A

Because you can add a lot of it and it does not increase viscosity due to its very high solub, and compact strucutre.

58
Q

Gum arabic structure

A

Backbone of galactose with galactose, arabinose and glucornic acid on side chains.

59
Q

Cellulose backbone

A

glucose in B1,4 linkage. So linear.

60
Q

How is MCC (microcrystalline cellulose obtained)

A

By acid treatment at high temperature which removes amorphous regions and preserves crystalline regions?

61
Q

What type of technique of drying of MCC is best suitable for flavour carrying? and for foam and emulsion stabilization?

A

If freeze dried, porous structure is formed and this is best suitable for flavour carrying and also for anticaking agent. While if the dried crystalline is broken down at high shear, small uniform particles are formed which can stabilize foam and emulsions.

62
Q

What are the three types of cellulose modification?

A
  1. Carboxymethyl cellulose (CMC)
  2. Hydroxypropyl cellulose (HPC)
  3. Methyl cellulose (MC)
63
Q

How many substituions can a glucose unit have?

A

max. 3

64
Q

What are the properties of CMC?

A
  1. Anionic
  2. Soluble in water. More soluble with higher degree of substitution on glucose as less interaction possible between chains.
65
Q

What are the properties of HPC?

A
  1. Soluble in water but insoluble at temp >45C.
  2. Soluble in ethanol
  3. High surface activity
66
Q

What are the properties of MC?

A
  1. Soluble
  2. Forms gels upon heating and restores original viscosity upon cooling. Gelling temperature depends on degree of substitution.
    3, High surface activity

Food Structuring (9 decks)

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