Lecture 9-Part 2 Flashcards

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1
Q

define ferulic acid

A

Ferulic acid is an organic compound belonging to the family of hydroxycinnamic acids, which are a type of phenolic acid., has a benzene ring and is what is naturally substiued on arabinoxylans

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2
Q
  • describe the structure of arabinoxylans
A

Is a linear xylan chain that is made of 1,4 linked Beta-D-xylopyranoysl. It has α-L-Arabinofuranosyl residues attached at 2,3 or 5th carbon. It is naturally subsitiuted by ferulic acid residuse on the arabonise.

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3
Q
  • where are arabinoxylans found and what is it
A

a non strach polysachride (pentoglycan) that is the main soluble fiber in wheat and corn and is also a major component of hemicellulose

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4
Q
  • what do ferulic acid residues form?
A

they form di ferulate bridges which results in covalent linkages between polymers aka crosslinking

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5
Q
  • how is the solubility of Beta-glucans related to its structure?
A

The beta 1,3 linkages cause a twist in the polymer chain which makes the otherwise rigid and linear chain to be more flexible. If this linkage didnt interrupt the ability to form tightly packed crsytaline structures it would be insoluble like cellulose because it decreases interactions with water molecules. But because it has been interupted there is more ineraction with water molecules as more OH are exposed so more hydrogen interactions so more soluble in water

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6
Q
  • describe how the structure of arabinoxylans relates to its solubility
A

The solubility depends on two things; degree of substitution and ferulic acid cross linking. The more substition there is the more soluble it will be since it interferes with the ability to be packed tighlty so instead there is loose packing and more interactions with water so increased solubility. But crosslinking by diferulate bridges will lower solubility since they form corvalent bonds that reduce solubility.

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7
Q
  • explain how the viscosity of beta glucans is related to its structure
A

At low shear rates the molecular weight of beta-glucan is what will increase viscosity, if it is increased viscosity increases

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8
Q
  • what flow behaviour does beta glucan exhibit?
A

It exhibits pseudoplastic, shear thining behviour so increase shear stress decrease in viscoity

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9
Q
  • describe the viscosity of araboxylans
A

shear thining pseudoplastic behaviours that are also influences by pH and molecular weight. Higher molecular weight, higher viscsity. At a pH more than 4 and less than 7 the acid allows for decreased electrostatic repulsion and therefore aggregation increases and therefore viscosity increases.

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10
Q
  • describe gelation of araboxylans
A

form a gel from the feruloyl residues becoming esterified to arabonise units

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11
Q
  • what does gelation strength of arabinoxylans depend on
A

depends on the arabinoxylan conentration, higher more gel, the molecular weight since as it increases the water absorbtion increases so gel increases, the A/X ratio if a higher ratio more A which means more gel, the ferulic acid content as gel depends on it

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12
Q
  • describe the role of arabixylans in emulsifaction and foaming
A

ferulic and p-courmic units are hydrophobic and are able to stick to oil surface and the hydrophilic polysachride chain is able to stay in water phase so reduction in the tension at the water/oil interface. This will create a thick coat on the emulsion droplets so they do not coalescence. It can also stabolize this in air/water interface foams

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13
Q
  • what are the food applications of arabinoxylans
A
  • nuetral taste and odor of gels and AX
    • high water absorbtion capacity
    • stable under acidic and heated conditions
    • gels resistant to syneresis which is when expel liquid
    • increased viscoity at low pH
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14
Q
  • Describe the mechanism of gelation of beta glucagn
A

it needs certain conditions to gel, it must have a molecular weight lower than 200 kDa to allow for molecules to have the needed mobility and they need a minimum concentration of 3%

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15
Q
  • explain why gel strength is correlated to proportion of triosyl units
A

this is because the arrangment of trysioyl units allow for a more stable and effective junction zone which is esssential for gelation. This is because the 1,3 flexibility allows for it to be in a form that allows for intermolecular interactions that are required during gelation

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16
Q
  • give a list of beta-glucan rich bran products
A
  1. oat flour
    1. oat bran
    2. concentrated oat brans
    3. oat and barley beta glucan extracts
17
Q
  • describe how oat bran is obtained
A
  1. dry milling to seperate bran from endosperm
    1. then bran is enriched with beta glucan
18
Q
  • describe how concentrated oat bran is obtained
A
  1. bran is further processsed, air classification is done to seperate beta glucagn from cell wall fragments and starch grnaules
    1. oil is removed by hexane extraction
19
Q
  • describe how oat and barley beta glucan extracts are obtained
A
  1. grain flour/bran is put in aqeuous ethanol and protien and starch is removed
20
Q
  • what are the applications of beta-glucan rich products in the industry and the % needed
A
  • whole grain oats and barley (3-5% beta glucan)
    • oat and barley flour (3-5%) can be used in plant based foods
    • oat bran (more than 8%)
    • Oat and barley concentrates (15-50%) used for health claims
    • oat and barley beta glucan extracts (more than 50%) is used as a nutritional supplement
21
Q
  • what are the positive effects that araboxylan has?
A

postive effects on colonic health (prebiotic), lipid metabolism and glycemic control

22
Q
  • explain wheat flour arabinoxylan water absobrtion and binding
A

it has a very high water binding capacity and can absorb water very well which will affect the moisture of bread dough, gas retention, loaf volume and texture which we dont want

23
Q
  • explain what must be added to flours to decrease water absorbing and binding
A

xylanases/hemicellulases must be added to break down arabinoxylan to decrease water binding and absorbing capcity since decreasing crosslinks and this will release water so gluten can form and a better more elastic dough will form and increase in size of gas cells.