1. 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

2. ENERGY transfer between enzymes, other molecules
Cellular Respiration: the process of using glucose to make energy (ATP) for the cell.
Aerobic Cellular Respiration (requires oxygen)
enzymes
6O2 + C6H12O CO2 + 6H2O
oxygen glucose carbon dioxide water
ENERGY transfer between enzymes, other molecules
ADP + Pi
ATP

3. Aerobic Cellular Respiration takes place in the mitochondria of cells.
It can provide up to 38 molecules of ATP per molecule of glucose.

4. Anaerobic Cellular Respiration (without oxygen)
also known as Fermentation
Alcoholic Fermentation:
C6H12O6
glucose
2CO2 + 2C2H5OH
carbon dioxide ethanol
provides 2 molecules ATP per glucose
done by yeast

5. Products of Alcoholic Fermentation
don’t drink alcohol

6. Making Rootbeer: 6 simple steps
Heat Water to ~40 degrees C (yeast like it)
Add sugar and dissolve
Add root beer extract
Add yeast
~27 degrees C
Chill and enjoy!

7. Lactic Acid Fermentation:
Glucose carbon dioxide + lactic acid
provides 2 molecules ATP per glucose
done by muscle cells
done by bacteria cells

8. Products of Lactic Acid Fermentation

9. Other products of fermentation - some are fermented by both yeast and bacteria
Idli, Dosas, Kimchee, Sausage, Kefir, sauerkraut, miso, tempeh, tamari, chutney

10. More products of fermentation

11. 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

12. 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

13. 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.

14. Milk is Water Protein (casein and whey) Fat Sugar (lactose) Vitamins
Minerals

15. How Does Milk Turn Into Yogurt?
Lactic acid Bacteria
>
Lactose
Lactic Acid
(Milk sugar)
Acid causes casein (milk protein) to denature and hold water into a semi-solid gel = yogurt

16. Milk Yogurt Bacteria produce acid Fat globule
Casein protein micelles (bundles)
10-7 meters in diameter
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
Fat globule

17. 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 pre-treatment:
Casein before heat
pre-treatment:
Casein after acid:

18. 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