FERMENTATION

• Classical Biotechnology

• Humans have been using this technology for

centuries

• Involves harnessing the wastes of bacteria

and/or yeast for products that humans

consume

• Big business

Cellular Respiration: the process of using

glucose to make energy (ATP) for the cell.

Aerobic Cellular Respiration (requires oxygen)

6O2 + C6H12O6 6CO2 + 6H2O

oxygen glucose carbon dioxide water

enzymes

ADP + Pi

ENERGY transfer

between enzymes,

other molecules

ATP

•Aerobic Cellular Respiration takes place

in the mitochondria of cells.

•It can provide up to 38 molecules of ATP

per molecule of glucose.

Anaerobic Cellular Respiration (without oxygen)

also known as Fermentation

Alcoholic Fermentation:

C6H12O6

glucose

•provides 2 molecules ATP per glucose

•done by yeast

2CO2 + 2C2H5OH

carbon dioxide ethanol

Products of Alcoholic Fermentation

don’t drink alcohol

Making Rootbeer: 6 simple steps

• Heat Water to ~40 degrees C (yeast like it)

• Add sugar and dissolve

• Add root beer extract

• Add yeast

• Ferment @ ~27 degrees C

• Chill and enjoy!

Lactic Acid Fermentation:

Glucose carbon dioxide + lactic acid

•provides 2 molecules ATP per glucose

•done by muscle cells

•done by bacteria cells

Products of Lactic Acid Fermentation

Other products of fermentation - some are

fermented by both yeast and bacteria

Idli, Dosas, Kimchee, Sausage, Kefir,

sauerkraut, miso, tempeh, tamari,

chutney

More products of fermentation

YogurtYogurt-like products have been made for millenia across Eastern Europe,

North Africa, Central Asia and India.

Contains bacteria that are “thermophilic” = heat loving

Two main types of Lactic Acid Bacteria

(Identified around the year 1900):

Traditional spontaneously fermented milks contain species that can reside in the human digestive tract:

• Lactobacillus fermentum,

• L. casei

• L brevis

• L plantarum (from picked vegetables)

• L acidophilus

Lactobacillus• meaning “milk” and “rod”

• over 50 different species

• found on plants and in the digestive system of animals such as cows and humans.

Lactococcus• meaning “milk” and “sphere” because of its shape

• found primarily on plants

• less common than lactobacillus

Commercial YogurtContains 2 species of bacteria specialized to grow well in milk (but can’t

survive inside the human body):

First,

Streptococcus

thermophilus is

more active,

then slows

down when

acidity reaches

0.5%

Next,

Lactobacillus

bulgaricus is

more acid

tolerant and takes

over until acidity

>1%

These bacteria work in symbiosis. Each bacterium stimulates the growth

of the other => acidifies the milk more rapidly than either partner on its

own.

Milk is

•Water

•Protein (casein and whey)

•Fat

•Sugar (lactose)

•Vitamins

• Minerals

LactoseLactic acid Bacteria

------------------------->

Acid causes casein (milk protein) to denature and

hold water into a semi-

solid gel = yogurt

(Milk sugar)

How Does Milk Turn Into Yogurt?

Lactic Acid

Milk YogurtBacteria produce acidCasein protein micelles

(bundles)

10-7 meters in diameter

Fatglobule

Acid causes

Casein bundles to

fall apart into

separate casein

molecules.

These rebind to

each other in a

network that traps

water.

=> makes a gel

Making Yogurt in 4 Simple Steps1. Start with Cow, Sheep, or Goat milk.

Casein before heatpre-treatment:

Casein after heat pre-treatment: Casein after acid:

2. Heat milk to 80 °C. Two purposes:• destroy existing bacteria

• “condition” the proteins = begins the denaturing process

(a whey protein molecule binds to a casein molecule which disrupts the casein bundles

allowing them to make short branched micelle chains)

3. Cool milk to 40 °C and innoculate with bacteria

4. Incubate at 30 °C to 45 °C

Incubation Temperature

• 40-45 °C takes 2-3 hours

Produces a coarse protein network with thick strands give firmness but easily leak whey

(a process called syneresis - the separation of liquid from the gel)

• 30 °C takes 18 hours

Produces a finer more branched delicate network that holds the liquid whey