Introduction to Biotechnology
• Lab 1C:
The Evolution of Cheese Making
Technology
The Complex Nature of Milk
• Milk supplies the calcium for building bones
and teeth, especially during adolescence
• Milk is 87% water
• However that’s a solvent for over 250 chemical
compounds, milk sugar (what is the name for milk
sugar_____?____) water-soluble vitamins and trace
minerals and salts
Protein
• Two main proteins make up milk:
• 80% Casein = milk protein
• 20% Whey = milk protein
• Micelles = an aggregation or cluster, of
molecules, often found in colloidal
dispersions
– The light reflecting from micelles makes milk white
• As long as milk keeps its normal acidity
level, about pH 6.6, casein remains stable
Protein Continued
• When the pH level decreases the milk forms lumps
or coagulates.
• Curds = The casein clumps that separate from the
liquid when milk coagulates
– When cooking with milk you can prevent curdling by using starch to thicken the milk
– If you want to coagulate milk, you can use the enzyme rennin or vinegar.
• Whey = protein found in the liquid that remains
after fat and casein have been removed from milk.
– Whey is also called serum protein
Fats
• Milk is an emulsion because small globules of fat
(lipid) are dispersed throughout the water
• Creaming = process in which some of the fat
droplets come together in larger clusters that rise
and float to the top of the milk
– These clusters rise to the surface because fat is less dense than the watery portion of
milk
• Cream = simply milk that is extra rich in emulsified
fat droplets
• The fat in cow’s milk are most complex lipids, over 400
different fatty acids
• Click For Milk Experiment
Carbohydrate
• Lactose or milk sugar is the main
carbohydrate
– Lactose provides food energy
– Also adds body to milk as well as a sweet flavor
– When milk is heated, lactose reacts with amino acids in the protein
(giving cooked milk a slightly caramel flavor)
– When you consume milk, lactose becomes available to the body because
of the enzyme lactase.
•
This enzyme breaks lactose down into galactose and glucose, which is used in the body for
fermentation during digestion.
Carbohydrate Continued
• Do you know someone who cannot drink
milk???
• People can be lactose intolerance = the inability to
digest milk due to the absence of the enzyme lactase
in the intestines
– People who are lactose intolerant cannot break down lactose in their
body. When they drink the milk they can have bloating, stomach cramps
and diarrhea.!!! -NOT FUN
Cheese
•
Cheese is made by coagulating the casein
protein in milk.
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Once the curds have formed, the whey is drained away.
(heating and cutting the whey helps this drain)
The curd is then treated and allowed to ripen
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During ripening, the cheese is hung for at least 60 days, some take months
Four main categories of cheese are based on moisture
content:
1.
Very hard cheese – parmesan and Romano
2.
Hard cheese – cheddar, Colby and provolone
3.
Semi-Soft cheese – Munster, Roquefort, and stilton
4.
Soft cheese – brie, camembert, and mozzarella
Unripened Cheese – cottage cheese and cream cheese
Cheese-making Procedure 1
Cheese-making Procedure 2
Cheese-making Procedure 3
Cheese-making Procedure 4
Improving Cheese-making
Purpose:
Which curdling agent produces cheese the fastest?
Which curdling agent produces the most cheese?
To examine numerical data for support of predictions.
To examine variables that can lead to invalid experiments.
Hypothesis: ______ is expected to produce the most volume of cheese in the
shortest amount of time because it _________________________.
Procedures:
1. Using a 10 mL pipet and pipet pump, transfer exactly 7 mL of whole milk into a labeled, 15
mL conical tube.
2. Using a pre-set micropipet, add 0.25 mL (250 uL) of one of the four curdling agents to the
7 mL of milk.
Use either: buttermilk, rennin, chymosin, or dH20 (- control) as assigned by your supervisor.
3. Cap the tube and gently mix by inverting 3 times. Record this “initial time”. __________
4. Place the milk-containing portion of the tube deep in your armpit, like a thermometer, and
incubate it there for at least 15 min.
5. Check for curdling every 5 minutes, recording the time to curdling in minutes. To check
for curdling, gently tilt the tube, careful to not breakup any curds. Curds are large lumps of
solidified milk. After 15 min, place the tube upright, at room temperature and check for
curdling every 15 min for 2 hours. If curdling has not occurred within 2 hours, continue
checking once every four hours. With the greatest accuracy possible, record the number of
minutes passed until the milk had curdled to the greatest extent.
6. If curdling has not occurred by the end of the class period, bring the tube home (keep at
room temperature) and back to class in 24 hours. Keep tube upright so any curds fall to the
bottom of the tube.
Procedures:
7. On return to the lab, measure the amount of
curds (solids) and whey (liquid) in the tube.
You may be able to read the volume of each
directly off the tube although it may be
difficult. Better yet, filter it as described
below, using a “whey-o-meter”.
8. If necessary, pour the whey and curds
mixture through a filter paper funnel into a 10
mL graduated cylinder (a “whey-o-meter”).
Determine the volume of whey collected in
the graduated cylinder, using a pipet if
necessary to measure small amounts. By
subtraction, determine the volume of curds.
Can you suggest other methods of
determining the amount of curds produced in
each treatment?
9. Record the data for your sample plus one
each of the other variable groups on the data
table below. Record the name of the person
from whom you have gotten data.
Fill in the Blank-o-Meter
Fill in the Blank-o-Meter
10. Using Excel®, the lab supervisor will collect each individual’s data to make a
class data table showing multiple replications of the experiment. Averages for
each variable group should also be recorded on this data table. Averaged data
is the best answer to an experimental question. Can you explain why?
11. Using Excel®, produce two graphs; one which shows the average time to
curdling for each enzyme treatment and one which shows the average volume
of curds produced by each enzyme treatment. Use the Excel® tutorial if
necessary.
12. Imagine you are an employee at a cheese curdling company and you
must summarize the results of your experiments and give your supervisor
the best answer to the scientific questions asked. Write a conclusion that
reports the Results of the experiment (answer to the purpose question)
including Evidence and Explanations for your findings. Discuss how well
the results support the hypothesis. Identify sources of Possible Errors in
the technique that may lead to variations in results (see next slide). Think
about the Practical Applications of the results of the experiment. Make a
recommendation to the cheese company supervisor about which curdling
agent should continue to be the focus of production. Include any variations
in the procedures that you think may improve the cheese production.
13. In the biotechnology industry, the work of others is reviewed and “OK’d”
by peers. This is called “witnessing”. When you witness data and analysis,
check for:
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Accuracy of statements (and that they make sense)
Completeness (R/E/E, PE, PA)
Evidence (numerical with units of measurement)
Grammatical and spelling errors
Make correction and suggestions right on the page,
For corrections, strike a single line through the error, correct it, and initial it.
For suggestions, write your suggestion in the margin, draw an arrow where it should be
placed and initial it.