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FNH 405 > Lectures 11-14 > Flashcards

Lectures 11-14 Flashcards

1
Q

Mother dough

A
  • continuously maintained
  • contains the microbial inoculum for subsequent doughs
  • made primarily of water and flour
  • rich in fermentable CHO (maltose)
  • low pH allows LAB to flourish
  • endophytes
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2
Q

Backstopping

A

take a piece of the mother dough from one batch and use it to start a new batch

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3
Q

Sourdough type 1

A
  • spontaneous and relies on the naturally present microflora
  • mixing flour + water, adding some of the previous batch’s mother dough
  • Saccharomyces cerevisiae NOT added
  • LAB/yeast are ‘fed’ daily w/ freshwater/flour
  • fermented at ambient temperature for 6-24hrs
    ph 3.8-4.5
    -rise due to CO2 production
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4
Q

Sourdough type 2

A
  • adding a starter culture of LAB to flour-water mixture -> acid tolerant Lactobacilli used
  • strain chosen
    a) fast acid producers
    b) produce desirable flavour compounds
  • Saccharomyces cerevisiae added as a leavening agent -> rise
  • temp >30 Celsius for 1 to 3 days; no extra feeding
  • pH < 3.5
  • pumpable liquid form and produced in bioreactors/tanks
  • liquid culture sold commercially to bakeries
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5
Q

Type 1 vs Type 2

A

type 1:
- pH 3.8 - 4.5 ‘
- thick dough (low DY)
- temp: 20 - 30

Type 2:
- pH < 3.5
- thin dough (high DY)
- temp: > 30

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6
Q

Dough yield

A

Formula: (flour mass + water mass) * 100/ flour mass

high DY -> more water and thinner dough
- faster acidification
- better diffusion of produced organic acids/secondary metabolites
- better access to substrates
- high temperature and water content -> enhances acid production

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7
Q

Sourdough type 3

A

type 2 dried
- microflora inactivated; heat-resistant LAB is used
- Saccharomyces cerevisiae added
- adding flavour/texture to the product
- dried using Drum drier and miller down after
- stream heat; minimal heat damage; no/minimal caramelization/Mailard rxn; > 113 -> acetic acid

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8
Q

Main factors of Sourdough

A
  • type of grain used
  • age of mother dough
  • DY
  • co-presence of other organisms
  • temp./season
  • industrial vs. artisanal bakery
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9
Q

LAB and Yeast Symbiosis

A
  • LAB -> high adaptable CHO metabolism (sugars) and acidification creates a low pH environment (proteases -> free amino acids for their growth)
  • Yeast -> flavour, leavening, breakdown of phytic acid = more mineral availability)
  • relationship between F. sanfransicisensis (process maltose) and k. humilis (can’t process maltose; acid-tolerant)
  • F. sanfransicisensis imports and processes maltose into glucose and glucose-6-phosphate vis isomerizes
  • glucose is released into the extracellular medium for use by K. humilis
  • K.humilis supplies F. sanfransicisensis with vitamins and minerals
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10
Q

Shelf-life stability

A

Retrogradation -> crust becomes leathery, flavour diminished

mould contamination and development of rope caused by bacillus spp.
- unpleasant odours
- discoloured, sticky bread crumbs

addition of sourdough to bread dough -> slow stale process, prevent ropiness and prolong mould period
- due to the acidification of acetic acid

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11
Q

Sourdough spoilage

A
  • prone to mould growth
  • baking -> good kill step
  • cooling bread before bagging to remove moisture
  • use preservatives -> calcium phosphate, potassium sorbate, calcium lactate -> inhibits growth of mould
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12
Q

Kefir

A
  • insoluble macroscopic particles
  • protein mostly casein
  • CHO mostly LAB exopolysaccharides
  • unique kefir polysaccharide
  • 1:1 glucose to galactose
  • LAB + AAB + yeast + maybe some fungi
  • hetero- and homo- LAB
  • assimilating
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13
Q

Kefiran

A
  • unique kefir polysaccharide
  • LAB symbiosis w/ saccharomyces cerevisiae: improves the quantity of kefiran made
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14
Q

LAB present in Kefir

A

Primarily Lactobacillus, Lactococcus, Streptococcus, Leuconostoc (90%)
- act to preserve the milk -> acetic/lactic acid; flavour

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15
Q

Yeast present in Kefir

A

mostly saccharomyces cerevisiae, kluyveromyces marxianus, kluyveromyces lactis, Candida kefir
- produces ethanol, CO2

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16
Q

Role of kluyveromyces lactis

A

intracellularly produces B-galactosidase
- breakdown of lactose into glucose and galactose

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17
Q

Role of LAB

A
  1. intracellular produces B-galactosidase
    - glucose -> homofermentative pathway
    - galactose -> Leloir pathways
  2. Lactose phosphorylated during transport and split by 6-phospho-B-galactosidase
    - glucose -> homofermentative pathway
    - galactose-6-phosphate -> Tagatose-6-pathways
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18
Q

Kefir Production - Traditional/home

A
  • initially aerobic, but O2 is consumed and becomes anaerobic
  • LAB -> combination of homo- and heterofermentative
  • lactic acid, acetic acid, diacetyl, acetaldehyde, CO2
  • yeast -> ethanol production
  • recover grains afterwards for re-use
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19
Q

Kefir Production - Industrial

A
  • milk content standardized
  • pasteurized -> rid of undesired microflora
    Starter culture
  • lactobacillus kefir, lactobillus kefiranfaciens
  • no yeast
  • anaerobic
    after 24hr add flavour, etc. and packages
  • final product -> 0.8% to 1.% lactic acid
  • tart flavour, smooth, viscous body
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20
Q

Cholesterol-lowering effects

A
  • kefir grains reduce CH levels in milk
    K. marianus -> ability to assimilate CH; put it in the grain
    L. plantarum -> inhibits host CH uptake -> bile salts hydrolase that cuts up bile salts and prevents lipid uptake
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21
Q

Milk

A

initially pH: 6.0-6.5
- composition standardized
skim milk; extra milk solids added to facilitate texture
- total non-fats milk solids: 12 -15%
- enhances water binding, prevents syneresis

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22
Q

Stabilizers for Yogurt

A

high water availability (~0.97-0.99)
- spoilage is not an issue

improves viscosity/body; minimizes syneresis; uniformity batch -batch; function at low pH

examples: gelatin, pectins, starches, whey proteins, locust/carob, ultrafiltered milk

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23
Q

What type of pasteurization does milk normally get?

A

High-temperature short time (HTST)
30 minutes, ~85 Celsius -> denatures whey proteins (alpha-lactalbumin and b-lactoglobulin)
- more protein unfolding = more water binding capacity

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24
Q

Gel-Formation

A

“acid-induced milk gel”
Pre-starter:
- whey proteins denatured w/ heat -> these interact w/ k-caseins via hydrophobic interactions and cross-link w/ k-caseins through disulphide bonds

Post-starter:
- acidification (protons) leads to charge neutralization facilitating more casein-casein interactions
Calcium phosphates leached out of micelle
- normal complexes w/ phosphoserine residues in casein - further destabilize micelles
- isoelectric point (pH ~ 4.6) gelation of caseins occurs

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25
Q

Key properties of Yogurt Starter

A
  • Freeze well
  • rehydrates/wakes up and grows well
  • make acid quickly - drop pH to required to target in 4-6 hours
  • resistant to bacteriophages
  • able to create the ‘right’ viscosity/body
  • no acid production at low temp
  • mild flavours/no off flavours
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26
Q

2 Starters in Yogurt

A

Streptococcus thermophilus (St) and Lactobacillus delbrueckii (Ld)
- thermotolerant bacteria
- both heterofermentative bacteria
- grown separately; different preferred growth conditions

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27
Q

Streptococcus thermophilus (St)

A
  • grows first, lowers pH of milk for Ld
  • anaerobic, but aerotolerant
  • more acid-sensitive; inhibited sooner

Proteolytic system:
- casein is degraded by cell envelope-associated proteases (CEPS) -> in St called Prts
- serine protease

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28
Q

Lactobacillus delbrueckii

A

hydrolases caseins peptides via PrtB -> peptides transported via various transporters for different size fragments
- hydrolyzed by peptidases to amino acids -> feed St. higher acid tolerance

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29
Q

Metabolism

A

Both microorganisms express cytosolic B-galactosidase
- glucose -> homofermentative pathways
- galactose -> exports galactose to pump in lactose via lactose permeases (Lacs)
- energetically favourable to use galactose and lactose permease to transport lactose

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30
Q

Protocooperation

A

shift pH of milk closer to optimal for Ld

CO2, formic acid, folic acid (St. -> Ld.) -> cofactor/precursors in purine biosynthesis

Purines (Ld -> St) -> St is capable of making them but in co-culture, all turned off

LCFA (St. -> Ld) -> growth for Ld; lack the genes encoding enzymes capable of making LCFA; synthetase, desaturase, dehydrase

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31
Q

Where is the CO2 coming from?

A

Urease (St. -> Ld) -> enzymes, breaks urea into ammonia and Co2

ammonia
- CO2 -> Ld -> purines
- controls acidity in the media; acting as a protein sink

32
Q

Exopolysaccharides (EPS)

A

modulate texture using high or low levels

potential issues -> excessive
- ropiness/stringiness
- undesirable; mask flavours; ‘slick’ mouthfeel

Controlled
- dec. temp = more EPS production

EPS -> homo- or heteropolymers; starts out as glucose-6-phosphate

33
Q

Yogurt - Acetaldehyde

A

Primarily flavour
- light green apples/ tartness
- hydrolysis of threonine; decarboxylation of pyruvate; oxidation of acetyl-CoA

34
Q

Yogurt Defect - overproduction of acid

A

pH < 4.0 and acid > 2.0% acid
- too high temp; cooling rate too low; acid production during storage
- control -> LAB strains sensitive to low pH or high temperature; incubate at 37 celsius

35
Q

Syneresis

A

yellow/green H2O floating on top
- occur if too much acid
- week gel formation
- stabilizer -> bind up the extra water -> inc. gell strength

36
Q

Yogurt stabilizers

A
  • act to improve viscosity
  • minimize syneresis (whey release)
  • uniformity batch-batch
  • must be functional at low pH
37
Q

Villi

A

“capsular” EPS produces -> stays attached to the cell wall
- musty flavour -> yeast (Geotrichrim candidum)
- yeast and LAB present
- velvet like surface; aerobic; catabolizes lactic acid (pH ~4.4) ; release protease that breakdown amino acids and release ammonia
- secretes lipases
- not homogenized; mesophilic cultures

38
Q

What is cheese?

A

cheese is the fresh or matured product obtained by the drainage after the coagulation of milk, cream, skimmed or partly skimmed milk, buttermilk or a combination thereof

39
Q

Coagulation in cheese production

A

liquid is removed from cheese through the coagulation of milk proteins
- casein micelles

40
Q

Three Coagulation mechanisms in cheese production

A
  1. Acid Coagulation
  2. Acid/heat coagulation
  3. Enzymatic coagulation
41
Q

Acid Coagulation

A
  1. drop pH to 4.6: isoelectric point of casein
    - addition of aid or lactic acid by LAB
    - neutralizes charges on casein micelle
    fresh cheese - 70-80% moisture
    can be strained or pressed to remove whey and reduce moisture

ex. cottage cheese, cream cheese, quark,

42
Q

Acid/heat coagulation

A
  1. Cooking to 90 celsius
    - denaturation of whey protein
  2. Drop pH to ~5.3
    - addition of acid

fresh cheese with 50-80% moisture
can be pressed to remove extra moisture
e. ricotta cheese, paneer

43
Q

Enzymatic Coagulation

A

Enzymes induce curd formation

Rennet: a mixture of enzymes found in the stomach of ruminant animals (main enzyme: chymosin, an aspartic protease)

Fungal proteases

Plant-derived proteases

Function: cleavage of k-casein

44
Q

Enzymatic Coagulation - 2 phases

A

Primary phase
- cleavage of k-casein on the exterior of casein micelles = reduction in negative charge
- micelles being to aggregate

Secondary phase
- residual negative charge in casein micelles reduced by free Ca2+; further aggregation occurs

45
Q

Three goals of the cheesemaker

A
  1. expel the correct amount of whey
  2. retain the correct amount of calcium phosphate
  3. incorporate the correct amount of NaCl (preserve)
46
Q

Cheese production steps

A
  1. setting
  2. cutting
  3. cooking
  4. draining/knitting/pressing
  5. salting/brining
    6 finishing/maturing/ripening
47
Q

Step 1: Setting

A

Rennet/chymosin is added to the milk
- chymosin-acid protease; most active at pH 5.5
- the rate of acidification important - rapid causes a loss of calcium phosphate - crumbly cheese

Culture may be added or slightly before rennet to allow ph drop

a) coagulation
- length of renneting affects curd firmness

b) acidification by LAB
- final pH 4.6-5.1
- the rate of pacification affects calcium phosphate retention
- pH affects curd firmness -> low pH = firmer curd

48
Q

Step 2: Cutting

A

curd is cut to initiate syneresis
surface area to volume ratio
- to inc. water removal, cut the curd into smaller pieces
smaller surd (grain sized) used for hard cheese, larger curds for softer cheese

49
Q

Step 3: Cooking

A

Curds and whey are cooked and stirred to help remove moisture
higher temp/longer time = drier curd
affect mineral retention, buffer capacity, lactic acid production

50
Q

Step 4: Draining/knitting/pressing

A
  • curd is separated from the whey
  • curd is allowed to fuse
  • added pressure is often used to facilitate moisture removal and knitting
51
Q

Step 5: salting/brining

A
  • further removal of whey from, the curd
  • provide an appropriate environment for ripening organisms
  • prevents spoilage microorganism growth
52
Q

Acidification

A

Fermentation of lactose to lactic acid by LAB
- naturally present; starter culture

Acid
- preserves cheese
- Inc., syneresis
- impacts enzymatic coagulation rate

53
Q

The rate of acidification affects

A
  • retention of colloidal calcium phosphate
  • curd firmness
  • gel syneresis
  • pH at the start of ripening
54
Q

Starter cultures microorganisms

A

Harder cheeses are made with thermophilic cultures
- more syneresis/moisture removal at higher temperatures

Mesophiles (< 39°C):
Lactococcus lactis subsp. lactis
Lactococcus lactis subsp. cremoris

Thermophiles (> 39°C):
Lactobacillus delbrueckii subsp. bulgaricus
Lactobacillus delbrueckii subsp. lactis
Lactobacillus helveticus
Streptococcus thermophilus

55
Q

Lactococcus lactis

A
  • Gram +ve cocci
  • Mesophilic (20-
    30°C)
  • Homofermentative
  • Acid production inhibited above 39°C
  • Cell death above 45°C
  • membrane transport consumes ATP
  • 1 lactose = 4 lactic acid
  • galactose: TGP pathway
56
Q

Lactobacillus delbrueckii/helveticus

A
  • Gram +ve rods
  • Thermophilic (40°C - 44°C)
  • Homofermentative
  • Used in high-temperature cooked
    cheese (< 65°C)
  • Protocooperative with Streptococcus
    thermophilus
  • antiporter transport of LacA Galactose is lost
  • 1 lactose = 2 lactic acid + 1 galactose
57
Q

Flavour development - three key components of cheese

A
  1. Fermentation of lactose to lactic acid
  2. Hydrolysis of lipids to fatty acids (lipases)
  3. Breakdown of casein to peptides, amino acids,and ammonia
58
Q

Bloomy-rind cheese

A

Ex. Brie, Camembert
Penicillium camemberti can be added as freeze-dried spores
Geotrichum candidum can be added directly to the milk or to the salt brine or sprayed on the surface

Pre-ripening conditions:
- rapid acidification w/ mesophilic cultures
- low pre-aging pH: 4.6-4.7
- no cooking or pressing
- moisture >50%
- dry salt

Yeasts grow first, consume lactate and raise pH
- Geotrichum candidum
- Kluyveromyces lactis
- Saccharomyces cerevisiae
- Debaromyces hansenii

Molds (Penicillium) follow later

Geotrichum candidum
- proteinase activity releases peptides that stimulate the growth of Penicillium camemberti

Penicillium camemberti
- appears after 6-7 days
- lactic acid metabiluzes, raising pH > 7.0
- allows entry of flavour-producing bacteria

59
Q

Why is bloomy-rind cheese softer near the exterior? A zonal cheesy gradient

A
  • pH inc. on the cheese surface and a pH gradient forms
  • CaPO4 precipitates at the rind as pH inc. and forms a gradient (high at the rind and low at the centre
  • softening from the inc. pH, precipitation of CaPO4 at the rind results in a zonal pattern of ripening
60
Q

Bloomy-rind cheese flavour

A
  • A synergistic effect between G. candidum
    and P. camemberti prevents bitterness
    from developing in the cheese
  • P. camembert releases proteinases that
    create large, bitter peptides
  • G. candidum and P. camemberti produce
    aminopeptidases and carboxypeptidases
    that break down bitter peptides
61
Q

Washed-rind cheese

A

Ex. Limburger, Talgeggio, Muenster

Pre-ripening conditions:
- similar to bloomy rind, except:
- slower acidification
- higher starting pH of 5.0 to 5.4

Yeasts (G. candidum) raise pH to ~6.0 within a few days of ripening, opening the way for
coryneform growth

Cheese is washed regularly with salt solution: which stops mold growth

62
Q

Brevibacterium linens

A
  • yeast
  • appears when surface pH rises above ~6
  • extensive proteolytic activity
  • volatile sulphur compounds and ammonia development = smelly cheese
  • gives the cheese a red-orange colour
63
Q

Interior Ripening - Cheese

A
  • The interior of most cheeses are
    anaerobic, inhibiting the growth of
    cheese yeasts
  • Flavour development is primarily
    the result of starter LAB (SLAB)
    and non-starter LAB (NSLAB)
  • Proteolytic cascades convert the
    casein to peptides, amino acids, and
    finally to flavour compounds
  • This is the dominant ripening method
    of common hard cheeses: Cheddar,
    Gouda, etc.
64
Q

Alpine (swiss) cheese

A

examples: Emmental
- S. thermophilus and L. helveticus work protocooperatively to ferment cheese after cooking
- S. thermophilus metabolizes lactose and excretes galactose back into the cheese
- L.helveticus imports galactose and uses it (Leloir pathway)
- Final pH = 5.1 - 5.3
- Brine in 20% salt and then ripen

65
Q

Alpine (swiss) cheese - Pre-ripening conditions

A
  • delayed acidification
  • cooked up to 50 Celsius
  • curd pressed
  • low salt
  • Warm temperature ripening (20°C - 24°C)
    encourages the growth of Propionibacteria:
    lactate -> propionic acid + acetic acid + CO2
  • CO2 is trapped inside, forming the ‘eye’ associated with alpine cheeses
66
Q

Propionibacterium freundenreichii

A
  • Gram +ve rods, anaerobic to
    aerotolerant
  • Use lactate as a substrate
  • Sensitive to NaCl
  • Optimal growth temperature 25°C
  • Tolerant to 55 °C
  • 3 Lactate = 2 propionate + acetate +
    CO2 + ATP
  • Lactate -> pyruvate is oxidized to acetate or pyruvate can be reduced to propionate through the wood-werkmen pathway
67
Q

Blue-veined cheese

A

Pre-ripening conditions:
- low pH of 4.5 - 6.0
- no cooking or pressing
- moisture 38-50%
- high salt

The interior aerobic environment required for Penicillium roqueforti
- No pressing: keeps space between curds
- Citrate heterofermentation by Leuconostoc cremoris and Lactococcus lactis
subsp. lactis bv. Diacetylactis produces CO2, fracturing the curds

68
Q

Penicillium roqueforti

A
  • Aerobic mould grows through cheese wherever oxygen is available
  • Carries out extensive lipolysis and proteolysis relative to other hard cheeses, leading to strong flavours
  • Converts free lipids to methyl ketones (fruity, floral, musty, spice, “blue cheese”)
  • Flavour intensity correlates with methyl ketone concentration
69
Q

Fish Spoilage

A

Relatively fast
- high water content in general
- historically, no access to refrigeration -> faster microbial spoilage
seawater harbour a large number of spoilage bacteria (psychrotophs)

fermentation allows for extending the edibility of the product in some form

70
Q

Fish - Post mortem

A

4 main steps following death:
Rigour mortis -> resolution of rigour -> autolysis -> microbial spoilage

All contribute to spoilage or if controlled via external factors, fermentation
- temperature, fish size, species

71
Q

Resolution of rigour

A

Proteolytic activity within muscle cells
disrupts actin/myosin associations

Muscles “relax”

72
Q

Fish - Fermentation Routes

A
  1. Fermentation via enzymes/autolysis
  2. Microbial Fermentation
73
Q

Fish - Alkaline Fermentation

A

The end product is ammonia
extensive autolysis occurs (post-mortem step 3) and salt represses unwanted microorganisms
Fish sauce pH < 7.0
- ammonia is a hallmark indicator that alkaline fermentation has occurred

pH range of the main classes of proteases
- aspartic proteases, cysteine proteases, serine proteases
main proteases in alkaline fermentation trypsin-like serine proteases
Endopetidases and exopeptidases

74
Q

Microbial Fermentation

A

Natural seas salt
Lactic acid could be generated by LAB even without CHO present
Common genera:
- Bacillus, staphylococcus
LAB: Tetragenococcus
- generally contributes to the breakdown of fish

75
Q

Post-Fermentation

A

Sauce allowed to settle
- The liquid removed is 1st grade

brine can be added to the solids
- 2nd grade but not as flavourful

solids can be ground and made into a paste

Airing out the sauce
- allows for the dissipation of “fishy” odours
- usually done out in the open with a cover

FNH 405 (3 decks)

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