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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
oxygen
enzymes
glucose
6CO2 + 6H2O
carbon dioxide water
ENERGY transfer
between enzymes,
other molecules
ADP + Pi
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
2CO2 + 2C2H5OH
glucose
carbon dioxide
ethanol
•provides 2 molecules ATP per glucose
•done by yeast
Products of Alcoholic Fermentation
don’t drink alcohol
Making Rootbeer: 6 simple steps
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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
Yogurt
Yogurt-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):
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
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
Commercial Yogurt
Contains 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
How Does Milk Turn Into Yogurt?
Lactic acid Bacteria
Lactose
(Milk sugar)
-------------------------> Lactic Acid
Acid causes casein (milk
protein) to denature and
hold water into a
semi-solid gel = yogurt
Milk
Casein protein micelles
(bundles)
10-7 meters in diameter
Yogurt
Bacteria produce acid
Acid causes
Casein bundles to
fall apart into
separate casein
molecules.
Fat
globule
These rebind to
each other in a
network that traps
water.
=> makes a gel
Making Yogurt in 4 Simple Steps
1. Start with Cow, Sheep, or Goat milk.
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
Casein after heat
Casein before heat
Casein after acid:
pre-treatment:
pre-treatment:
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