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VEN 124 Section IV. The Malolactic Fermentation. Lecture 12: The Biology of the Lactic Acid Bacteria. Reading Assignment: Chapter 6, pages 244-250; 262-278.

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ven 124 section iv

VEN 124 Section IV

The Malolactic Fermentation

slide2

Lecture 12:

The Biology of the Lactic

Acid Bacteria

slide3

Reading Assignment:

Chapter 6, pages 244-250;

262-278

slide4

The “malolactic fermentation” refers to the conversion of the grape acid malate to lactate conducted by members of the lactic acid bacteria

malolactic fermentation
Malolactic Fermentation

COOH

CH2 CH3 + CO2

CHOH CHOH

COOH COOH

Dicarboxylic Monocarboxylic

Can give up Can give up

2 protons 1 proton

lactic acid bacteria characteristics
Lactic Acid Bacteria: Characteristics
  • Prokaryotes: no membrane around nucleus
  • Gram positive
    • Peptidoglycan
    • Teichoic acid
  • Divide by binary fission
lactic acid bacteria divisions
Lactic Acid Bacteria: Divisions
  • Group I: Strict homofermenters
  • Group II: Facultative heterofermenters
  • Group III: Strict heterofermenters
homofermentative metabolism
Homofermentative Metabolism

85% of Glucose Lactic acid

Glucose Pyruvate via glycolytic pathway

HO-C-C-CH3 Pyruvate

HO-C-CH-CH3 Lactate

O O

NADH2

NAD+

O OH

heterofermentative metabolism
Heterofermentative Metabolism

Organisms metabolize glucose via the pentose phosphate pathway.

End products can vary depending upon level of aeration and presence of other proton and electron acceptors. Acetyl-phosphate can be converted to acetate and ATP or reduced to ethanol without ATP production.

pentose phosphate pathway
Pentose Phosphate Pathway

Lactic Acid Bacteria can also metabolize pentoses such as ribose, arabinose and xylose, via the pentose phosphate pathway.

Acetyl-phosphate leads to the generation of acetate and ATP exclusively in pentose metabolism.

slide12

Pentose Phosphate Pathway

Glucose

Phospho-6-gluconate

ATP ADP

NADP+

NADPH

CO2

Ribulose 5-phosphate

NADP+

NADPH

Xylulose 5-phosphate

Acetyl-phosphate

Glyceraldehyde 3- phosphate

NADH

NAD+

ADP

ATP

ADP

ATP

(glycolysis)

Acetate

Acetaldehyde

Pyruate

NADH

NAD+

Ethanol

Lactate

lactic acid bacteria genera
Lactic Acid Bacteria: Genera
  • Oenococcus
  • Pediococcus
  • Lactobacillus
  • Leuconostoc
oenococcus
Oenococcus
  • O. oeni
pediococcus
Pediococcus
  • P. damnosus
  • P. parvulus
  • P. pentosaceus
  • P. acidilactici
lactobacillus
Homolactic on hexoses

L. bavaricus

L. casei

L. homohoichii

L. curvatus

L. saki

L. plantarum

Heterolactic on hexoses

L. fermentum

L. brevis

L. buchneri

L. fructovorans

L. hilgardii

Lactobacillus
leuconostoc
Leuconostoc

Wine species of Leuconostoc have been reclassified as Oenococcus.

lactic acid bacteria prevalence in wine
Lactic Acid Bacteria: Prevalence in Wine
  • Only O. oeni is found at low ( 3.5) pH
  • Pediococcus and Lactobacillus grow at pH values above 3.5.
deacidification
Deacidification
  •  Titratable acidity by 0.01 to 0.03 g/L because of H+ fixation
  •  pH by 0.1 to 0.3 units
  • Important for high acid wines
  • May be undesirable in low acid situations
effects of malolactic fermentation1
Effects of Malolactic Fermentation
  • Deacidification
  • Bacterial stability
bacterial stability
Bacterial Stability
  • Consume nutrients that would otherwise be available for other organisms
  • Produce toxins (bacteriocins) that may inhibit growth of other bacteria
  • Prevent malolactic fermentation from occurring in bottle
malolactic fermentation in bottle
Malolactic Fermentation in Bottle:
  • Increases turbidity due to cell growth
  • Produces noticeable gas as CO2
  • May produce polysaccharide material
    • Haze
    • Ropiness
  • May raise pH allowing growth of spoilage organisms
  • Does not allow for control of flavor/aroma profile of wine
effects of malolactic fermentation2
Effects of Malolactic Fermentation
  • Deacidification
  • Bacterial stability
  • Flavor changes
acetic acid
Acetic Acid
  • From sugar metabolism
  • Amount formed versus ethanol depends upon aeration and presence of other electron acceptors
  • Level produced can be significant
  • Can also be produced from citrate metabolism
  • Low levels can be made by Saccharomyces
slide27

Acetic Acid

OH

H3C-C=O

diacetyl
Diacetyl
  • Made from pyruvate
  • Multiple pathways to pyruvate
  • 1-4 mg/L adds complexity “buttery”
  • Over 4 mg/L dominates “movie popcorn butter/rancid”
  • Low amounts can be produced by yeast
  • Dicarbonyl compounds important in the chemical generation of wine grape characters
slide30

Pathways to Diacetyl

Citrate

Acetate

Oxaloacetate

Pyruvate

Pyruvate

CO2

Pyruvate

Acetaldehyde*

Acetaldehyde*

Acetyl CoA

Acetaldehyde*

Pyruvate

-Acetolactate

O O

H3 C-C-C-CH3

Diacetyl

CO2

slide31

Acetaldehyde* refers to “active acetaldehyde” which indicates the enzymatically bound form of acetaldehyde with the coenzyme thiamine pyrophosphate.

acetoin
Acetoin
  • Also produced from pyruvate
  • Can be derived from diacetyl
  • Generally present below threshold of detection
  • May be important in other chemical reactions in wine
slide34

Pathways to Acetoin

Citrate

Acetate

Oxaloacetate

Diacetyl

CO2

Pyruvate

NAD+

NADH

Acetaldehyde*

Pyruvate

Acetoin

-Acetolactate

O OH

H3 C-C-CH-CH3

CO2

flavor changes associated with malolactic fermentation3
Flavor Changes Associated with Malolactic Fermentation
  • Acetic acid
  • Diacetyl
  • Acetoin
  • 2,3-Butanediol
2 3 butanediol
2,3-Butanediol
  • Derived from acetoin
  • Generally present below threshold of detection
  • Mild “sweet alcohol” flavor that borders on bitterness
  • Can be produced by yeast
slide37

2,3 Butanediol

O OH

Acetoin

H3C-C-CH-CH3

NADH

NAD+

HO OH

2,3 Butanediol

H3C-CH-CH-CH3

flavor changes associated with malolactic fermentation4
Flavor Changes Associated with Malolactic Fermentation
  • Acetic acid
  • Diacetyl
  • Acetoin
  • 2,3 Butantediol
  • Ethyl lactate
ethyl lactate
Ethyl Lactate
  • “Generic fruit” character
  • Ester of lactate, a monocarboxylic acid

H

O OH

H3C-C-O-C-C-CH3

H

H

flavor changes associated with malolactic fermentation5
Flavor Changes Associated with Malolactic Fermentation
  • Acetic acid
  • Diacetyl
  • Acetoin
  • 2,3 Butanediol
  • Ethyl lactate
  • Diethyl succinate
diethyl succinate
Diethyl Succinate
  • “Generic fruit” similar to ethyl lactate
  • Ester of succinate, a dicarboxylic acid

H

O

H H

O

H

H3C-C-O-C-C-C-C-O-C-CH3

H

H H

H

flavor changes associated with malolactic fermentation6
Flavor Changes Associated with Malolactic Fermentation
  • Acetic acid
  • Diacetyl
  • Acetoin
  • 2,3 Butanediol
  • Ethyl lactate
  • Diethyl succinate
  • Acrolein
acrolein
Acrolein
  • Made from glycerol
  • Creates an intensely bitter taste when combined with phenolic compounds
slide44

Acrolein

Glycerol

-hydroxypropionaldehyde

H H

Acrolein

H2C=C-C=O

flavor changes associated with malolactic fermentation7
Flavor Changes Associated with Malolactic Fermentation
  • Acetic acid
  • Diacetyl
  • Acetoin
  • 2,3 Butanediol
  • Ethyl lactate
  • Diethyl succinate
  • Acrolein
  • Other compounds
other compounds
Other Compounds

The Lactic Acid Bacteria are capable of producing numerous other aroma compounds, especially from the degradation of amino acids. It is likely that some of these compounds are also being produced during growth in wine.

tartrate
Tartrate

Some strains of L. plantarum and L. brevis are capable of metabolizing tartrate to acetic acid, referred to as “tourne disease” by Pasteur. This is always undesirable.

flavor changes associated with the malolactic fermentation
Flavor Changes Associated with the Malolactic Fermentation

Amounts of specific compounds produced are strain dependent and dependent upon the composition of the juice and level of aeration.

slide49

In the next lecture we will learn how to manage the malolactic fermentation in the winery.