Lect 10 : Bread Fermentation

Question 1

How does the purpose of bread fermentation differ from the fermentation of other products like milk, vegetables (kimchi), wines etc?

Answer 1

The primary purpose is to convert less perishable raw materials into more perishable, but also more FUNCTIONAL products (conversion of flour to bread so you can eat it)

For other products like milk, vege… the primary purpose is to extend shelf life of highly perishable raw materials with high water activity / moisture

Question 2

What flour is most commonly used in bread making? Why?

Answer 2

Wheat, as they contain gluten (a protein), which is important in maintaining structure of bread and contribute to airy, fluffy texture

Question 3

What are the 4 major components of wheat flour?

Answer 3

1. Carbohydrates – 75% of carbs is starch + simple sugars, cellulose, fibre
2. Protein – 8-16%
   - gluten
3. Enzymes : alpha/beta amylase (digest glycosidic bonds between amylopectin and amylose)
4. some free amino acids

Question 4

What is gluten protein made up of?

Answer 4

Gluten is a protein which is made up of 2 proteins : Gliadin and glutenin

Gliadin : high glutamine content (viscosity due to H bonding)

Glutenin : elastic due to proline (a.acid) content

Question 5

[PROCESS AIDS]

How does salt improve the qualities of bread?

Answer 5

Introduction of salt : ionic interaction between amino acids and salt and causes cross linking of gluten, toughening the gluten structure

It also affects fermentation rate, enzyme reactions, taste etc (shelf life due to lowered water activity)

-note : salt slow’s yeast fermentation as it attracts water, but yeast needs water

Question 6

[PROCESS AIDS]

How does adding sugars aid in processing/ improve the qualities of bread? [3]

Answer 6

1. Boost rate of fermentation (more substrate for yeast to work on)
2. Enhance taste through Maillard reaction
3. enhance appearance due to non-enzymatic browning (Maillard reaction)

Question 7

[PROCESS AIDS]

How does alpha/beta amylases aid in processing and improve the qualities of bread? [3]

However, adding too much enzymes could be a problem. What problem does it cause? [1]

Answer 7

1. Increased starch hydrolysis for fermentation (starch converted to more digestible forms)

2. Increase loaf volume
Amylase functionality may be related to the reduction of dough viscosity during starch gelatinization, thus prolonging oven rise and resulting in an increased bread volume

3. Soften crumb (inner of bread) which delays staling – since starch is more hydrolysed and less starch to reaggregate to cause staling

If there is too much enzymes, the dough will become sticky due to excess free sugars and cause overbrowning

Question 8

[PROCESS AIDS]

How does malt powder improve the qualities of bread?

Answer 8

It is a source of alpha/beta amylase to hydrolyse starch

Question 9

[PROCESS AIDS]

How does proteases aid in processing?

Answer 9

It weakens the gluten network so that the dough becomes softer, therefore reducing mixing time and improving machinability

Question 10

[PROCESS AIDS]

How does lipases aid in processing / improve the qualities of bread?

Answer 10

Breaks down lipids into glycerol and free unsat FA

Free unsat FA is then converted into lipid hydroperoxides, which act as oxidants to form disulfide bonds in gluten, strengthening the gluten network and stabilizing gas cells

Question 11

[PROCESS AIDS]

How do fats aid in processing / improve the qualities of bread? [2]

Answer 11

1. 0.1-0.2% or higher helps gluten expand and stretch, expanding loaf volume.
2. It delays gluten development, leading to a softer, cake-like texture in bread
   - Fat bonds to the gluten proteins preventing them from bonding with one another and forming gluten chains. This makes the final bread more tender,

Question 12

[PROCESS AIDS]

What kinds of yeast nutrients are used, and how do they aid in processing / improve the qualities of bread? [2]

Answer 12

Yeast nutrients, such as ammonia salts of sulfate/chloride; and phosphate or carbonate salts help to adjust the pH

• offer suitable pH for yeast ferm

Question 13

[PROCESS AIDS]

How do vitamins aid in processing / improve the qualities of bread?

Answer 13

Improves the nutritional quality of bread through enrichment/fortification

Question 14

[PROCESS AIDS]

What are the 2 kinds of dough improvers?

How do they aid in processing/ enhance properties of bread?

Answer 14

1. Reducing agents weaken dough structure by breaking up disulfide bonds/cross-links in gluten, decreasing mixing time
2. Oxidising agents such as vit C (ascorbic acid) and K bromate increase elasticity of dough by strengthening the gluten network, and improving gas retention

Question 15

[PROCESS AIDS]

What kind of substance is usually used as preservatives in bread, and how does it improve the quality of bread?

Answer 15

Anti-fungal agents such as salts of weak organic acids.

They improve the microbial quality of bread by inhibiting the growth of mould.

Question 16

[PROCESS AIDS]

How do emulsifiers aid in processing/ enhance properties of bread?[4]

How do the presence of emulsfiers affect appearance of bread?

Answer 16

They increase water absorption, gas retention, decreasing proofing time and reduce staling rate (emulsifiers can bind water to lipids/air, promote gluten-lipid-starch interactions– starch : hydrophilic, lipid : hydrophobic, gluten : depends)
.
.
.
.
.

Emulsifiers lead to smaller, consistent holes on bread and thus having a better texture.

Question 17

What are the 3 main purposes of dough mixing/hydration?

Answer 17

1. Blend and hydrate the dough ingredients
2. Develop the dough to produce a viscoelastic structure that is able to retain gas without rupturing
3. Aerate the dough

Question 18

What are the 2 purposes for aerating the dough in dough mixing?

Answer 18

1. provide nucleation sites (air pockets) for CO2 diffusion and bubble growth during proofing
2. provide oxygen to assist in dough development, via initial aerobic yeast multiplication

Question 19

What is the main microorganism used to ferment bread? (normal bread)

Answer 19

Baker’s Yeast, Saccharomyces Cervisiae

Question 20

Is the fermentation by Saccharomyces Cervisiae aerobic or anaerobic?

Answer 20

Both, Saccharomyces Cervisiae is facultative anaerobic

Initially, metabolism is aerobic (TCA cycle), glucose is broken down into CO2 and aerobic metabolism causes yeast to grow

After 30 min, fermentation becomes anaerobic (glycolysis – alcoholic fermentation), producing alcohol and CO2 as end products [glucose –> pyruvate –> ethanol + CO2]

Question 21

[SOURDOUGH]
For a sourdough starter culture, what form is it usually in?

Answer 21

Dry form

Question 22

[SOURDOUGH]
For sourdough starter culture, what is the ratio of LAB to yeast used and why?

Answer 22

LAB : Yeast = 100 : 1.

This is because LAB is not as metabolically active as yeast

Question 23

[SOURDOUGH]
What is a sourdough starter culture?

Answer 23

A defined or undefined culture of lactobacilli, usually with yeast maintained over time, propagated and continued for the purpose of leavening

Question 24

[SOURDOUGH]
What is sourdough?

Answer 24

A flour dough fermented with or containing a symbiotic culture of LAB, dominantly lactobacilli, plus yeasts to leaven bread. It is used as an ingredient/starter culture for sourdough bread.

Question 25

What is sourdough bread?

Answer 25

Bread that is leavened by sourdough/sourdough starter culture.

Question 26

Sourdough bread always have a sour flavour / odour. True or False?

Answer 26

False, it depends on the acids produced by the specific strains of lactobacilli involved.

Question 27

In sourdough bread, the ratio of lactic acid : acetic acid = 4:1. Why is it in this ratio?

Answer 27

This ratio allows for the development of the sour flavour of sourdough bread. Flavour = taste + aroma Lactic acid contributes to the sour taste while acetic acid contributes to the sour aroma.

Question 28

To achieve the ideal ratio/ a ratio close to the ideal ratio of lactic acid : acetic acid = 4:1 in sourdough bread, name 2 species of LAB you will use.

Answer 28

Homofermentative LAB : 2 moles of lactic acid from 1 mole of glucose - **Companilactobacillus Farciminis** Heterofermentative LAB : 1 mole of lactic acid + ~1 mole of acetate - **Fructilactobacillus Sanfranciscensis**

Question 29

What are artificial sourdoughs?

Answer 29

Sourdough bread that involves direct acidification with lactic acid and does not involve fermentation with LAB

Question 30

state the flow of making sourdough bread

Answer 30

Refer to lect notes pg 31

Question 31

In sourdough bread, at what pH is sourness detected?

Answer 31

around pH 4, with a pH <4, there will be a distinct **mild** sour taste

Question 32

The final pH of sourdough bread is low at around 4 and thus inactivates the enzyme amylase. How does amylase inactivation improve the qualities of sourdough bread? [4]

Answer 32

1. Improves water-binding capacity of starch (since less amylase to hydrolyse starch, if starch is hydrolysed then there is less starch molecules to cross link and trap water) 2. Decrease starch retrogradation and staling (since WBC increase and less water lost, so wont stale) 3. Gluten swelling and dough becoming more elastic 4. Better gas retention

Question 33

The sourdough LABs show antimicrobial activity. What metabolites do LABs produce and what 2 kinds of MOs do they inhibit

Answer 33

1. Anti-bacterial activity - production of bacteriocins, substances which inhibit other gram positive bacteria (e.g. plantaricin by Lactobacillus Plantarum) 2. Anti-fungal activity --organic acids, especially 2 carbon organic acids, inhibit mould

Question 34

How does sourdough LAB improve the nutritional quality of bread? [2]

Answer 34

1. **Phytic acid** It breaks down phytate, a naturally occurring metal chelator in cereals. With the breakdown of phytate, an antinutritional factor, mineral bioavailbility increases 2. **Gluten** - Proteases, peptidiases in sourdough LAB can break down gluten to a certain extent, thus gluten content in sourdough bread is decreased, gluten intolerant people may be able to consume the sourdough bread due to reduced allergencity

Question 35

What benefits, in terms of bread quality, does sourdough bread have over normal yeast fermented bread? [5]

Answer 35

1. [Microbial] prolonged shelf life due to production of acids which inhibits spoilage microbes 2. [Sensory] Increases loaf volume and delayed staling 3. [Sensory] Improves bread flavour (sour flavour contributed by lactate and acetate, **diacetyl**, esters etc) - since initial aerobic ferm by yeast (TCA) produces citrate, then the LAB ferments citrate into diacetyl 4. [Sensory] Improves texture (rye sourdough bread, which does not contain much gluten, thus bread as softer texture) 5. [Nutrition] Improves nutritional quality (mineral availability and gluten tolerance)