Bubbles in bread

Question 1

What are the steps involved in bread making from the wheat

Answer 1

1. milling 2. mixing the flour 3. Fermentation and baking

Question 2

T or F : the hard wheat will give more starch damage than soft wheat

Answer 2

true

Question 3

T or F : hard wheat is better because it has higher than 9% damaged starch

Answer 3

false it is not better because over 9% wheat damage you have sticky bread

Question 4

T or F : bread from sprouted wheat are better quality

Answer 4

false, they lesser the quality because of the presence of a-amylase which doesn’t let the starch ferment during the doug fermentation step

Question 5

Yeast will convert ___ to CO2 and ___

Answer 5

maltose will be converted to CO2 and ethanol

Question 6

what is the goal of the milling step?

Answer 6

making the starch available for the enzymes amylase for breaking them down into sugar for fermentation by the yeasts

Question 7

What are the 4 class of proteins identified by the osborne fractionation?

Answer 7

1. Albumin 2. Globulin 3. Prolamin 4. Glutelin

Question 8

Albumins are soluble in :

Answer 8

water

Question 9

Globulins are soluble in :

Answer 9

water with dilute salts

Question 10

Prolamins are soluble in :

Answer 10

70% ethanol

Question 11

Glutelins are soluble in :

Answer 11

soluble in dilute acids or base

Question 12

Glutenins are responsible for the ___ of the bread while gliadins are responsible for the ___

Answer 12

glutenins : strenght gliadins : viscosity

Question 13

gluten is a mixture of two class of proteins :

Answer 13

1. gliadins 2. glutenins

Question 14

The ___ creates disulfide bridges in the bread

Answer 14

glutenins-HMW

Question 15

What are the two types of glutenins?

Answer 15

LMW and HMW

Question 16

T or F : the gliadins will be responsible for the disulfide bridge

Answer 16

false, it is the glutenins

Question 17

T or F : disulfide bridge can also be found in LMW-glutenins

Answer 17

True, the disulfide bridge are also found int he LMW glutenins but less. the disulfide bridge are covalent bonds.

Question 18

Glutenins/ or gliadins are more present in gluten?

Answer 18

they are present 50% /50%

Question 19

The network formed by the gluten (gliadin and glutenin) is due to what type of interactions ?

Answer 19

1. hydrophobic
2. s-s (covalent) by the glutenins
3. hydrogen bonds

Question 20

What can you do to know if you will have good baking behaviour from a cultivar?

Answer 20

you can separate the proteins by SDS page and some bands will indicate good baking behaviour while others will be predictive of bad baking behaviour

Question 21

which part of the HMW glutenins are responsible mostly for the disulfide bridges?

Answer 21

the n terminal contains most of the thiol groups

Question 22

the disulfide bridge are intermolecular or intramolecular between the glutenins?

Answer 22

both

Question 23

How can you measure the elasticity of a bread ?

Answer 23

using the micro-mixograph : t is a spoon that measures the mixing over time, at first the dough is watery and over time it becomes a dough and it becomes harder for the spoon to move around. There is also something that measure the resistance of the bread mixture to the spoon.

Question 24

What are two ways you can access the quality of flour?

Answer 24

1. Separate the proteins from the cultivar using SDS page
2. Look at the mixing behaviour using the micro-mixograph

Question 25

what does the area under the curve represents in the micro-mixograph?

Answer 25

it represent the work require to mix a dough

Question 26

how do you read the micro-mixograph ?

Answer 26

you can see that good flour will develop resistance quickly and can maintain it while the poor flour will develop resistance quickly but will not be able to maintain it.

Question 27

which enzyme is used for the volume enhancement of dough

Answer 27

transglutaminase

Question 28

what are the enzymes seen in class used in the bread development

Answer 28

1. transglutaminase
2. xylinase

Question 29

what is the reaction catalysed by the transglutaminase?

Answer 29

can make a cross-link (peptide bond) between the peptide chains by connecting the lysines and glutamine

Question 30

what is the enzyme used that targe the proteins inside bread to improve the loaf volume ?

Answer 30

transglutaminase

Question 31

what is the enzyme that target the carbonhydrates in bread ?

Answer 31

the xylanase

Question 32

What are the two kinds of arabinoxylans?

Answer 32

highly substituted or less branched

Question 33

What is the backbone of arabinoxylan and the side chains?

Answer 33

the backbone is beta 1-4 linked residues and the side chains are arabinosyl side chains

Question 34

which of the arabinoxylan is water. soluble?

Answer 34

the highly branched because the unsustituted can link water-insoluble cellulose and form an unsoluble polymer

Question 35

both xylose and arabinose are pentoses, and therefore arabinoxylans are sometimes referred to as ____

Answer 35

pentosans

Question 36

at which position is the arabinosyl side chains connected to in the xylose reside

Answer 36

o2 or o3

Question 37

GH enzymes are xylinase and the GH stands for

Answer 37

glycoside hydrolase

Question 38

GH__ are more tolerant to branching than GH__

Answer 38

GH10 are more tolerant to branching than GH11

Question 39

what is the proposed mechanism for the use of xylanase as a bread improver ?

Answer 39

Question 40

which one of the xylanase is best for increasing the loaf volume?

Answer 40

the less tolerant to branching because it converts the WU-AX into WE-AX and WE-AX. The coating at the air bubble interphase remains more or less the same but the viscosity of the dough increases which reduces the coalescence rate of the bubbles

Question 41

why are xylanase tolerant to branching not good for the loaf volume ?

Answer 41

because you need a minimum lenght of the AX to be able to coat the bubble and when it is tolerant, then you will convert some of the WE-AX into smaller chains that will not prevent the coalscence

Question 42

why does the GH10 increases coalescence and reduced the air volume

Answer 42

because it will be tolerant to the branched AX that is found at the air bubble interphase and will reduce the film of the air bubbles.

Question 43

____ xylanase are isolated from bacterium pseudoalteromonas and have their best acitivty between 0-60˚C

Answer 43

psychrophilic

Question 44

psychrophilic have their best activitiy between ___ and __˚C

Answer 44

0 and 60

Question 45

T or F : the increased activity of the psychrophilic GH8 enzymes at lower molecule mobility is due to a bigger groove of the enzyme

Answer 45

false, it is due to the flexibility of the groove because here you can see that the groove is the same size.

Question 46

exam. ** what is the difference between the psychrophilic and thermophilic enzyme ?

Answer 46

1. thermophilic enzymes have a lot of cross-links that make the structure less flexible and psychrophilic have less of the disulfide and salt bridge
2. the a.a. in the groove are hydrophobic and flexible and so this helps at catching the substrates

Question 47

T or F : GH8 (psychrophilic) is even better at increasing the loaf volume

Answer 47

true

Question 48

T or F : the loaf volume enhancement effect of GH8 (psychrophilic) is due to its psycrhophilic nature

Answer 48

false, here the GH10 is also psychrophilic and the loaf volume not enhanced

Question 49

What are the wheat inhibitors we saw in class ?

Answer 49

1. TAXI
2. XIP inhibitor

Question 50

Why would you need to increase the dose of xylinase you use in some wheat ?

Answer 50

because there arre multiple isoform of TAXI-type and XIP-type inhibitor of xylinase and so this will reduce your activity

Question 51

What are the advantages of using GH8 endo-xylanase for the bread baking

Answer 51

1. acitivity at room temperature (during dough rising)
2. supposed to be sensitive to the brnaching like the GH11
3. it is not inhibited by the endo-xylanase inhibitors endogenous to wheat.
4. it is rapidely inactivated at baking temperautre