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Y2S1_FST2110 - Microbiology and fermentation > Lect 10 : Bread Fermentation > Flashcards

Lect 10 : Bread Fermentation Flashcards

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1
Q

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

A

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

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2
Q

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

A

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

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3
Q

What are the 4 major components of wheat flour?

A
  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
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4
Q

What is gluten protein made up of?

A

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

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5
Q

[PROCESS AIDS]

How does salt improve the qualities of bread?

A

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

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6
Q

[PROCESS AIDS]

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

A
  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)
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7
Q

[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]

A

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

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8
Q

[PROCESS AIDS]

How does malt powder improve the qualities of bread?

A

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

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9
Q

[PROCESS AIDS]

How does proteases aid in processing?

A

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

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10
Q

[PROCESS AIDS]

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

A

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

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11
Q

[PROCESS AIDS]

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

A
  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,
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12
Q

[PROCESS AIDS]

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

A

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
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13
Q

[PROCESS AIDS]

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

A

Improves the nutritional quality of bread through enrichment/fortification

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14
Q

[PROCESS AIDS]

What are the 2 kinds of dough improvers?

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

A
  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
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15
Q

[PROCESS AIDS]

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

A

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

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

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16
Q

[PROCESS AIDS]

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

How do the presence of emulsfiers affect appearance of bread?

A

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.

17
Q

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

A
  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
18
Q

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

A
  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
19
Q

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

A

Baker’s Yeast, Saccharomyces Cervisiae

20
Q

Is the fermentation by Saccharomyces Cervisiae aerobic or anaerobic?

A

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]

21
Q

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

A

Dry form

22
Q

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

A

LAB : Yeast = 100 : 1.

This is because LAB is not as metabolically active as yeast

23
Q

[SOURDOUGH]
What is a sourdough starter culture?

A

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

24
Q

[SOURDOUGH]
What is sourdough?

A

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.

25
Q

What is sourdough bread?

A

Bread that is leavened by sourdough/sourdough starter culture.

26
Q

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

A

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

27
Q

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

A

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.

28
Q

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.

A

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
29
Q

What are artificial sourdoughs?

A

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

30
Q

state the flow of making sourdough bread

A

Refer to lect notes pg 31

31
Q

In sourdough bread, at what pH is sourness detected?

A

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

32
Q

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]

A
  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
33
Q

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

A
  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
34
Q

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

A
  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

  1. 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
35
Q

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

A
  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
  1. [Sensory] Improves texture (rye sourdough bread, which does not contain much gluten, thus bread as softer texture)
  2. [Nutrition] Improves nutritional quality (mineral availability and gluten tolerance)

Y2S1_FST2110 - Microbiology and fermentation (12 decks)

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