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Fermentation

Metabolic process in which carbohydrates and related

compounds are partially oxidized with the release of energy in

the absence of any external electron acceptors. The final

electron acceptors are organic compounds produced directlyfrom the breakdown of the carbohydrates

Slides thanks to V. Trinetta

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Examples of Fermented Foods

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Carnobacterium

Enterococcus

Lactococcus

Lactobacillus

Lactosphera

Leuconostoc

Oenococcus

Pediococcus

Streptococcus

Teragenococcus

Weissella

Vagococcus

LACTIC ACID BACTERIA

Oenococcus oeni

Lactobacillus

Major Groups of Fermentative Microorganisms

11 Gram-positive genera

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The lactic acid bacteria are mesophiles:

10oC < range < 40oC

25oC < Toptimum < 35oC

some 5 or 45oC

4 < pH< 8

some 3.2 or 9.6

LACTIC ACID BACTERIA GROWTH

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All produce lactic acid from hexoses

As fermenting organisms, they do not have a functionalTCA cycle

Energy is obtained by substrate-level phosphorylation whileoxidizing carbohydrates

LACTIC ACID BACTERIA

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LAB can be divided into two groups

lactic acid homofermentative

lactic acid, ethanol and CO2 heterofermentative

LACTIC ACID BACTERIA

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Anaerobic glycolysis for glucose utilization

Glucose2 Pyruvate 2 Lactate

Net energy yield: 2 mole ATP/mole glucose

HOMOFERMENTATIVE LAB

ATP

ATP

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GlucoseLactic acid (~50%) + Ethanol + CO2

Can also form acetate

Net energy yield: 1 mole ATP/mole glucose

Additional biochemical pathways to obtain energy

HETEROFERMENTATIVE LAB

ATP

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THE PROPIONIC BACTERIA

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Saccharomyces

Found naturally on grapes

Many strains are commercially available

Aerobic or anaerobic metabolism

Alcohol is produced anaerobically

Glucose Ethanol CO2

THE GENUS SACCHAROMYCES

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GLUCOSE

2 ATP

4 ATP

Hexose

Isomerase

2 Lactate

2 ATP

4 ATP

1 ATP

2 ATP

Phosphoketolase

Lactate Ethanol

PYRUVATE

Propionyl-Coa Ethanol

2 H

CO2

Acetic

acid

Lactate

Propionate,acetate

, CO2

Propiona

te

2 H

succinat

e Succiny

l-CoA

AB

C D

E

F

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FOOD PRESERVATION/ SHELF LIFE EXTENSION

IMPROVE ORGANOLEPTIC CHARACTERISTIC

INCREASE NUTRITIONAL VALUE

WHY WE FERMENT FOODS???

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Worldwide production of some fermented foods

Food Quantity (t) Beverage Quantity (hl)

Cheese

Yoghurt

Mushrooms

Fish sauce

Dried stockfish

15 million

3 million

1.5 million

300 000

250 000

Beer

Wine

1000 million

350 million

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Natural fermentation

Controlled fermentation

CONTROLLED VS. NATURAL

FERMENTATION

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Lactic starters always include bacteria that convertsugars to lactic acid, usually:

Lactococcus lactis subsp. lactis,

Lactococcus lactis subsp. cremoris

Lactococccus lactis subsp. lactis biovar diacetylactis.

Where flavour and aroma compounds such as diacetylare desired the lactic acid starter will includeheterofermentative organisms such as:

Leuconostoc citrovorum

Leuconostoc dextranicum

(single, mix or multiples strain, mix or multiples species)

SOME EXAMPLES OF STARTER

CULTURES:

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Succession

Multiple strains involved in fermentation of somefood products

Interdependency between strains

Growth and death of one strain allows growth ofanother strain

Speed ripening of cheese ($)

Time

CFUor

PFU

Bacteria

Bacteria

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