lec 6 bread and baking technology Flashcards
what ingredients are in bread?
-Flour
– Water
– Yeast
– Salt
what are the Processes for creating colloidal structures?
-Mixing
– Fermentation
– Oven
– Storage
what Transformation happens when baking?
Transformation of a liquid foam to a solid foam
what types of Cereals are there?
*Wheat (Triticum aestivum, T.Durum)
– Bread and other foods, feed, biofuel
* Rye (Secale cereal) – Bread (sour dough and crisp bread)
* Triticale (Hybrid of wheat and rye) – Feed
* Barley (Hordeum vulgare) – Beer, malt liquors, feed
* Oat (Avena sativa) – Feed, porridge, dairy alternatives
* Rice (Oryza sativa) – Food, beer
* Maize/Corn (Zea mays) – Food, feed, high fructose corn syrup, biofuel
what is The wheat kernel made up of?
Endosperm – cells filled
with starch granules in
protein matrix (75-85%)
Bran (8-10%)
Aleurone layer – part of endosperm, separated by
bran (6-9%)
Germ (2-3.5%)
what is the difference in quality between winter and spring wheat?
Winter wheat
* Sown in autumn – harvest following year
* Lower protein content
* Cakes and cookies
* Dominating in Sweden (85%)
* New varieties similar to spring wheat are being introduced
Spring wheat
* Sown in spring – harvest late
summer
* Higher protein content
* Bread
* Internationally dominating
what qualities does soft weat have?
Soft wheat (weak)
* Endosperm breaks along cell
walls during milling
* Many small flour particles, free
starch granules
* Little starch granule damage –less water absorption
* Weak protein-starch interaction
* Lower protein content (8-10%)
what qualities does hard weat have
Hard wheat (strong)
* Endosperm fractures through cells during milling
* Large and irregular flour
particles, low amount of small
particles
* More damaged starch granules
– higher water absorption
* Strong protein-starch
interaction
* Higher protein content (12-
14%)
can we use Newly milled flour for baking?
no, oxidation is necessary
– Often chemicals are used for oxidation e.g. ascorbic acid or KBr
* Complex and not completely understood process
– Most likely chemical changes in proteins and polar
lipids
what can influence the bread volume?
Protein content and quality
what 4 protein types are there in wheat?
- Albumins
- Globulins
- Prolamins
- Glutelins
Albumins
water ‘soluble’
Globulins
soluble in salt solutions
Prolamins
soluble in 70% ethanol
Glutelins
dispersible in dilute acid
What is gluten?
Gluten is a group of proteins found in wheat, barley, rye, and their derivatives.
* Gluten provides elasticity to the dough
* Approx. 80% protein and 10% lipids
* Main proteins – gliadin (prolamin fraction) and glutenin (glutelin fraction)
amino acid composition of gluten?
– Amino acid composition: glutamine (34-40%),
proline (13-20%), cysteine (1-3%)
– Few charged amino acids
– Insoluble in water and salt solutions
– Gives viscoelasticity to the dough
– Forms a 3D polymeric network with embedded
starch granules and other components
what are Gliadins?
- Monomeric protein with
intramolecular S-S bridges - MW 25-100 kDa
- Contributes to dough viscosity
and extensibility
what are Glutenins?
- Polymeric protein with intra- and intermolecular bridges.
- Ultra-high MW ≈ 20 000 kDa
- Contributes to dough elasticity and strength
how do Gliadin and glutenin associate?
through S-S bridges
what is the lipid content in wheat?
1-2% lipids
-Polar ≈ 50% (Triglycerides
Not surface active)
-Non-polar ≈ 50% (Glycolipids,
Phospholipids –>Surface active!)
what ratio is most beneficial for bread volume?
High ratio of polar/non-polar lipids
what do Polar lipids form?
lamellar liquid-crystalline phases
what does the polar lipid formation of the lamellar liquid-crystalline phases aid in?
Aids the stabilization of expanding gas bubbles upon baking
what do the Wheat cell wall polysaccharides contain?
Pentosans (e.g. arabinoxylan), β-glucan (low solubility in wheat) etc
what is the percentage of water soluble pentosans?
1-1.5%
what is the percentage of water insoluble pentosans?
2.5%
how can the Wheat cell wall polysaccharides form gels?
after oxidation.
what does wheat starch contiain?
Amylose and Amylopectin
what is the percentage of amylose in wheat starch?
20-28%
what is the percentage of Amylopectin in wheat starch?
72-80%
what is the shape of amylose?
mainly linear
what is the shape of Amylopectin?
branched polysaccharide
what is gelatinization?
Gelatinization is the swelling and bursting of starch granules when they are heated in the presence of water.
how does the release of amylose molecules from starch granules occur during gelatinization?
they Leach from granules
how does the release of amylopectin molecules from starch granules occur during gelatinization?
Limited leaching – remain in
granule remnants
what is Retrogradation
Retrogradation refers to the process in which the gelatinized starch molecules, which have been dispersed in a solution during heating, reassociate and rearrange themselves into a more ordered structure upon cooling. It is essentially the opposite of gelatinization.
Reassociation of starch molecules: As the gelatinized starch solution cools, the amylose and amylopectin molecules begin to realign and reassociate with each other. This reassociation results in the formation of a more ordered and crystalline structure.
Water expulsion: As the starch molecules reassociate, they expel water molecules from the gel network. This leads to the formation of tighter bonds between starch molecules and contributes to the thickening and firming of the gel.
Texture changes: The retrogradation process leads to changes in the texture of starch-containing foods. For example, retrogradation contributes to the firming of cooked pasta and the staling of bread. In desserts and other products thickened with gelatinized starch, retrogradation can lead to the formation of a firmer and sometimes gritty texture over time.
what is syneresis
Syneresis is the process in which a gel or gel-like substance expels liquid, usually water, and contracts or shrinks. This expulsion of liquid occurs after gel formation, typically during storage or when the gel is subjected to mechanical stress
when does retrogredation start for amylose?
– Starts within minutes after
baking – completed within 48h
– Gives syneresis
when does retrogredation start for amylopectin?
– Starts several hours after
baking – completed within 2
weeks
– Contributes to bread staling
when does Starch gelatinization occur?
Gelatinization occurs upon heating in the presence of water
at what temp does granule swelling start?
– Granule swelling starts at approx. 45 °C
– Amylose leaches from granules
what temp is Loss of crystallinity at?
at approx. 62-64 °C
what is pasting?
polymers align (may gel upon
cooling)
what happens after gelatinizsation?
Gelatinization is followed by
retrogradation (i.e. recrystallization) of
starch polymers
what does α-amylase degrade starch into?
dextrins and sugars
what happens when α-amylase degrades starch to dextrins and sugars?
– Decrease in viscosity
– ‘Falling number’: α-amylase activity in a flour
– Blending of flours
–> gives constant ‘Falling number’
The falling number test measures the time it takes for a plunger to fall through a heated and stirred flour-water slurry. This time is inversely related to the α-amylase activity in the flour. Higher α-amylase activity results in faster starch degradation and a lower falling number, while lower α-amylase activity leads to slower starch degradation and a higher falling number. The falling number is an important parameter for assessing flour quality and predicting its performance in baking processes.
what is the Macromolecular composition of dough
(including hydrating water)?
Damaged starch
Starch
Protein
Pentosans/Cell wall PS
When is the dough sufficiently mixed?
Development in dough rheology during hydration and mixing
* Gluten
– Physical ‘cross-linking’
* Hydrophobicity and H-bonding
– S-S cross-linking
– Interaction with water and other dough components
Dough Rheology: Dough should become smoother and cohesive during mixing, with even water distribution and changes in elasticity and viscosity indicating gluten development.
Gluten Formation: Proper mixing aligns and bonds gluten proteins, creating a continuous network crucial for texture and volume in baked goods.
Hydrophobicity and H-Bonding: Hydrophobic interactions and hydrogen bonding between gluten proteins, along with S-S cross-linking, strengthen the gluten network during mixing.
Interaction with Water: Water hydrates flour, initiating gluten formation, and interacts with other dough components to ensure uniform hydration and proper gluten development
what is the dough?
a foam
what is Bubble creation aided by?
by decrease in surface tension
– Proteins and polar lipids
– Bubbles initially covered by proteins – forms stiff
surface layer
– Upon expansion lipids play an increasingly
important role
– Viscosity of continuous phase important
* Starch gelatinization
* Pentosans/cell wall polysaccharides
what is used for Fermentation/Proofing in bread baking?
- Yeast (Saccharomyces cerevisiae)
– Uses approx. 3% of flour CO2 and EtOH
– Creates volume, porosity and aroma - Sour dough – Lactobacilli produce lactic and acetic
acid
what happens during baking (Temperature increase)?
- Fermentation bubbles are retained as foam
during proofing & baking - Bubble surface layer hardens
- limits excessive growth of bubbles
even crumb structure - Baking heats and ́sets ́ the structure as a
sponge by gelatinizing the starch - The crust forms on drying the starch gel
below the glass transition temperature to
form a solid, brittle layer
what are some storage related changes in bread during staling?
(except microbial)
- Complex phenomenon of physico-chemical changes
- Increased softness of crust
- Increased firmness of crumb
- Increased crumbliness
- Increased whiteness
- Loss of aroma and taste, development of ”stale” taste
- Crumb softness recovered (to some extent) when
bread is reheated
what happens during staling?
- Water migration from crumb to crust and between components in the bread
- Changes in gluten
- Starch retrogradation (Amylopectin, slow)
How to prevent/delay staling?
- Storage temperature – maximum staling at approx. 4-6°C
- Control water content and distribution
- Enzymes
- Emulsifiers
- Starch source and treatment
- Starch composition
- Starch-lipid complex formation
how is staling affected by emulsifiers (surfactants)?
- Some polar lipids form inclusion complexes with amylose and longer
amylopectin chains (monoglycerides, lyso-lecithin, fatty acids etc.) - Hydrophobic tail of emulsifier enters the apolar cavity of the amylose or
amylopectin helices - Disturbs the recrystallization (retrogradation) of starch
