Bread / bakery products (physics)

Question 1

What is the formula of the water activity ?

Answer 1

Pvapor / P saturation = aw

Question 2

Why is there a hysterisis loop in the adsorption/desorption water activity graph

Answer 2

because when there is small pores in the food, the water will get absorbed by capillary suction and for this reason, the water will take more time for desorption than for adsorption because it first needs to condense before being vaporised

Question 3

What kind of information can you get from the moisture isotherm ?

Answer 3

the crystalline state of the food product. For example here in the graph I, the sugar would be amorphous because the water is taken fast and in the case of the graph 3, the sugar would be crystalline

Question 4

how would you interpret this graph?
dark = starch white = deffated starch

Answer 4

here we can see that at lower relative humidity of the air, the water content of starch will be the same defatted starch, this means that starch takes up water faster than deffated starch

Question 5

What does the C represents in this formula?

Answer 5

C is the bet isotherm constant and it is related to the heat of adsorption. Lower is the heat of adsorption and the easier it is ffor the water to adsorb

Question 6

what is the Ma in this formula ?

Answer 6

it is the maximum amount of water vapor before it turns into water

Question 7

____ is a mixture of proteins that forms the visco-elastic mass of grains and provides cohesiveness, viscosity and elasticity

Answer 7

gluten

Question 8

what is the role of water in making the dough?

Answer 8

1. Dissolve the molecules
2. activate the enzymes
3. formation of bonds between the macromolecules

Question 9

Can you explain this graph?

Answer 9

This is the starch gelatinisation occuring the dough development. At first the viscosity increases because of the swelling of the granules. Then the viscosity decreases because of the leaching of the amylose from the granules. this amylose will form a network and the viscosity will iincrease back again (full-line-cross-linked)

Question 10

Can you identify each peaks on this DSC curves for starch gelatinisation

Answer 10

Question 11

Waxy and Corn starch have high ___ and low ____

Answer 11

high amylopecting and low amylose (waxy doesn’t have amylose)

Question 12

What information can the DSC of a starch give us?

Answer 12

can give us information on the starch present (qualitative more than quantitative information).

Question 13

Gluten composition:

• Polymeric glutenins give ____
• Monomeric gliadins give ____

Answer 13

strength & elasticity
dough viscosity

Question 14

Can you give some of the quality compositional parameters of bread? (3)

Answer 14

1. amount of proteins
2. degree of damaged starch
3. Gluten composition

Question 15

T or F : increasing the level of damaged starch is good for the loaf volume of bread

Answer 15

false/true : it depends on the level of damaged starch, when too much is present you will have water intake too rapidely and this will lead to a rapid increase in the viscosity preventing the CO2 of expanding and decreasing the loaf volume

Question 16

T or F : the more protein there is inside your flour the better it is for the dough loaf volume

Answer 16

false, the proteins compete with starch for water and so they can lower the dough viscosity and increase the strenght of the dough too much preventing in th eformation of air cells by CO2 build up

Question 17

T or F : the waxy rice is good for loaf volumes

Answer 17

false, it doesn’t contain amylose so there no gel strength, no elasticity, low volume

Question 18

What can be used to replace the proteins in the case of gluten-free bread

Answer 18

gluten gives elasticity and strenght to the dough. polysaccharides that are often used are hydroxypropyl methyl cellulose, guar gum, arabic gum and modified cellulose

Question 19

what is the role of starch in bread making

Answer 19

starch is responsible for the gelling and elasticity because of the networks it forms when it gelatinise. Without starch (amylose) there is no gel strenght, no elasticity and so low volume of bread

Question 20

What are the factors that impact the water hydration ?

Answer 20

1. the particle size
2. concentration of damaged starch
3. the protein content

Question 21

Smaller particle size leads to ____water hydration which leads to ___ loaf volumes because of the ____

Answer 21

faster
lower bread volumes because of the higher viscosity

Question 22

Low levels of damaged starch is beneficial because :

Answer 22

beneficial effect due to easily accessible amylose which can leach out better an increase the viscosity of the coontinuous phase

Question 23

high levels of damaged starch is detrimental because :

Answer 23

due to over-hydration and large increase in the viscosity too rapidely (before the CO2 build up)

Question 24

Is high protein content good or bad for the bread quality

Answer 24

bad because it will interfere with the starch by disruppting the uniformity of the starch gel because of the competititon with starch for the water molecules

Question 25

What can be done to reduce the negative effect of proteins on the starch network?

Answer 25

adding hydrolysate enzymes : cutting the proteins will lead to lower MW and so smaller effect of the disruption of the network formed by the starch an so can be better.

Question 26

The dough has a ____ behaviour

Answer 26

strain hardening

Question 27

why does dough has a strain hardening behaviour

Answer 27

because when the dough is stretched (increasing strain) the entanglements will become harder and so the viscosity of the dough increases.

Question 28

The strain hardening behaviour is due to :

Answer 28

1. the gluten network
2. the branching between the polysaccharides present in the dough

Question 29

what is the strain hardening index (n)

Answer 29

The strian hardening is the index is an indication of how strain hardening is your system and so give informtion on the elasticity. higher value and the higher elasticity and bubble stability. You need a strain hardening value over 1 to have good baking loaf volume

Question 30

What happens when the strain hardening index is lower than one ?

Answer 30

you will not have enough elasticity in the dough. This means that the behaviour could be strain softening which will not prevent the coalescence of you bubbles an dwill lead to lower bread loaf volume

Question 31

T or F : retrogradation is related to water evaporation

Answer 31

the retrogradation is related to the amylopectin and amylose change in structure and not the bread evaporation. during over time water migration becomes free and avalaible and can migrate and then diffuse. so the change in structure is not relate to water evaporation but it is related to the water migration and then diffusion.

Question 32

Amylose can link other amylose molecules by forming ___ while aymolpetin forms ____ and ____

Answer 32

amylose : hydrogen bonding
amylopectin : intramolecular association and hydrogen bonding

Question 33

T or F : the amylose is linear so it usually stalks better on each other and is more prone to retrogradation

Answer 33

true because it can more easily form hydrogen bonds

Question 34

retrogradation of ___ is fast (first 2 days) while retogradation of ___ takes more time (more than 2 days)

Answer 34

fast: amylose
slow : amylopectin

Question 35

____ retrogradation is responsible for bread firming

Answer 35

Amylopectin

Question 36

____ amylopectin molecules show more retrogradation

_____ chain length distribution shows more retrogradation

Answer 36

Larger
Narrower

Question 37

T or F : Cereal amylopectin is shorter than pea and potato amylopectin, and thus the retrogradation is less.

Answer 37

true

Question 38

Can you explain this graph ?

Answer 38

so the steps of retrogradation / stalling is related to water migration is various steps :

1- the starch go back into a crystalline state because of their interaction and so less space for the water to be in these regions and so become free

2- the water diffuse out of the bread by molecular diffusion

3- the water in the crumb migrates to the crust because of its low water content and the crumb become harder and the crust become softer. this is unwanted and so there is no more crunchyness.

Question 39

T or F : there is more stalinig when the bread is kept at fridge temperatures

Answer 39

true

Question 40

What is the effect of freezing the dough

Answer 40

the granules are dammaged by the crystals and when the dough is thawed the starch amylose leach out fast which leads to harder and lowe volume of bread

Question 41

what is the effect of pH on the dough ?

Answer 41

• *lowering the pH (yellow)** : you are increasing the viscosity and the dough strenght because of the leaching of the amylose from the starch granules
• *very low pH (pink)** : chains will be too small for the network formation an so the dough strenght and viscosity is very low

Question 42

how does the additives reduce the retrogradation?

Answer 42

1. prevent the amylose and amylopectin from recrystallization
2. prevent the water migration

Question 43

What are the type of additives added to limit the retrogradation? (3)

Answer 43

Addition of CHO (sugars and polysaccharides)
Addition of fat
Addition of cyclodextrin

Question 44

How does sugars and polysaccharides prevents retrogradation?

Answer 44

1. They will bind water and decrease the free water amount and so the water migration (because they bind water)
2. They will reduce the recrystalilization of amylose / amylopectin (by being in the way of their re-crystallization0

Question 45

How does fat reduces the retrogradation?

Answer 45

can make complex with amylose and so limits the amylose-amylose interactions

Question 46

How does cyclodextrin limits the retrogradation?

Answer 46

Amylose/lipid/starch complex, which prevents the amylose from recrystalization

Question 47

why is lubrification good in the case of air bubbles ?

Answer 47

When the bread is expanding. the bubbles moves past each other and if there is no lubrification the bubbles that are coated with starch will move past each other and rupture but if there is lubrification, the mobility of the air cells will not rupture the air cells. So it decreases the coalescen and so there is more bubbles and smaller bubbles. Frnech bread doesn’t contaain any fat and this is why it is harder and contains bigger air bubbles.

Question 48

T or F : the addition of fat leads to smaller air bubbles

Answer 48

true because it provide lubrification of the bubbles that slows down the coalescence

Question 49

What is the effect of fat addition to a dough?

Answer 49

1. softening of the bread (increase in volume because more air bubbles)
2. decrease in te staling (decrease in the weight because of more evaporation of water)

Question 50

why do you have two types of fat in the case of laminated products ?

Answer 50

for the lamination you need two types of fat because you do not want the layers to touch so that you have lamination. So the fat that is used inside the dough is softer (lubrification) and the roll-in fats (flaky layers) needs to be hard and so it needs to be of high melting point because you want it to stays between the layers when heating and not hooze out. For croissant for example, the rolling is little softer because somewhere the dough touches and sometime nots and so croissant are a mix of lamniatiom and not.