Lecture 9-Part 2

Question 1

define ferulic acid

Answer 1

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

Question 2

• describe the structure of arabinoxylans

Answer 2

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.

Question 3

• where are arabinoxylans found and what is it

Answer 3

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

Question 4

• what do ferulic acid residues form?

Answer 4

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

Question 5

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

Answer 5

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

Question 6

• describe how the structure of arabinoxylans relates to its solubility

Answer 6

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.

Question 7

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

Answer 7

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

Question 8

• what flow behaviour does beta glucan exhibit?

Answer 8

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

Question 9

• describe the viscosity of araboxylans

Answer 9

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.

Question 10

• describe gelation of araboxylans

Answer 10

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

Question 11

• what does gelation strength of arabinoxylans depend on

Answer 11

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

Question 12

• describe the role of arabixylans in emulsifaction and foaming

Answer 12

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

Question 13

• what are the food applications of arabinoxylans

Answer 13

• 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

Question 14

• Describe the mechanism of gelation of beta glucagn

Answer 14

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%

Question 15

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

Answer 15

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

Question 16

• give a list of beta-glucan rich bran products

Answer 16

1. oat flour
   
   2. oat bran
   3. concentrated oat brans
   4. oat and barley beta glucan extracts

Question 17

• describe how oat bran is obtained

Answer 17

1. dry milling to seperate bran from endosperm
   
   2. then bran is enriched with beta glucan

Question 18

• describe how concentrated oat bran is obtained

Answer 18

1. bran is further processsed, air classification is done to seperate beta glucagn from cell wall fragments and starch grnaules
   
   2. oil is removed by hexane extraction

Question 19

• describe how oat and barley beta glucan extracts are obtained

Answer 19

1. grain flour/bran is put in aqeuous ethanol and protien and starch is removed

Question 20

• what are the applications of beta-glucan rich products in the industry and the % needed

Answer 20

• 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

Question 21

• what are the positive effects that araboxylan has?

Answer 21

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

Question 22

• explain wheat flour arabinoxylan water absobrtion and binding

Answer 22

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

Question 23

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

Answer 23

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.