pH Measurements – Applications in Food Science
http://virtuallabs,hmm .nmsu.edu/
So how is pH related to your life? The pH of cleaners is important because it often dictates their ability to kill bacteria.
Why is pH so important? When pH is too acidic or too basic, living things cannot grow, and are often killed. This is why
cleaning solutions are generally either very basic (like Chlorox or oven cleaner) or very acidic (like toilet bowl cleaner,
lemon juice or vinegar). We can also use very hot temperatures to kill bacteria as well.
Foods are (or were) living things. When living things die, or when we pick fruits and vegetables, the nutrient supply to
their cells is stopped. No nutrients means that the cells will eventually run out of energy and no longer be able to
metabolize. Normal every day bacteria that are always present on living things will start to break down the food and
eventually the food will decompose.
One job of a food scientist is to create food formulations and use different food processing techniques to preserve
foods.
Food scientists use a combination of heat, low pH and lack of air (sealing foods in a jar or can) to both kill bacteria, AND
prevent recontamination of foods. While many bacteria are killed simply by heating foods to boiling for a few minutes,
there are a few bacteria that can survive this intense heat. The bacteria do this by becoming dormant. Some bacteria
encase themselves in a sort of shell (called a spore) and can remain this way for YEARS. One of the most dangerous
species that become dormant is Clostridium botulinum. C. botulinum grows only in an environment without oxygen (in
an anaerobic environment). This means that even though we heat food AND seal the food by putting it in a jar or a can,
this bacteria can still grow (very slowly). When this bacteria grows, it also produces a toxin that is lethal to humans. A
very small amount consumed when we eat food that is not properly processed can lead to a rapid death.
How can we prevent this organism from growing? Scientists have found that as long as the pH of the food is at or below
4.6, even the spores of C. botulinum will be destroyed. This means there is no bacterial growth, and no toxin is
produced.
So how does a food scientist go about creating a food that tastes good, and is safe? This lab will take you through the
steps of calibrating a pH meter (most measurement devices should be calibrated regularly) and how to design an
experiment to text different formulations for a new type of corn salsa.
At the conclusion of this activity you should be able to:
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Explain how a pH meter can be calibrated using a double standard calibration.
Explain the importance of calibration, labeling and cleanliness when performing scientific tests
Explain how the researcher (you) decided to set up your experiment (your experimental design)
Write the procedure used during the experiment
Set up a data ( raw data and averages) for all tests you performed
Create an appropriate graph to display your results
Draw conclusions as to the best formulation to use, and why you chose the formulation
Determine next steps you would need to take to verify that what you have created is “sellable”.
Finally, a colleague has just handed you the abstract to an article that discusses whether pH 4.6 is “safe”. Read
the abstract and determine whether you need to go back and reformulate your Salsa, based on the results of
this study.
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Part I. Choose: The pH scale and pH meter calibration
1. The range of the pH scale ________________________
a. Lower numbers represent ___________________
Substance
Lemon juice
Vinegar
Soft drinks
Coffee
pH (given)
pH (measured)
pH indicator paper measure
pH? Use the indicator paper
to identify the
“approximate” pH of lemon
juice, coffee, egg whites and
milk of magnesia.
How does a food’s acidity
relate to safe storage?
Milk
Water
Saliva
Blood
Egg Whites
Baking Soda
Milk of Magnesia
Magnify the bacteria. You
will see that the cell, when
dormant, is actually
encapsulated by hard spore
casing. This makes the
bacteria very resistant to
heat (it won’t die) at 100 C
2. Why is C. botulinum harmless in the environment but deadly in anaerobic conditions? Be specific in your
answer.
3. If foods are being canned or jarred, what pH is “safe” to prevent the growth of C. botulinum?
4. What is the difference between an acid food and a low acid food?
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5. Which category is more acidic?
6. What is the concern with the salsa?
7. What is the purpose of calibrating a pH meter? What is a 2 point calibration?
8. How do you choose your calibration standards?
Part II. Choose Testing/Adjusting pH from the blue bar menu to continue
In this part of the lab activity you will identify the components of the food scientist’s controlled experiment.
2. Purpose or goal of the experiment of the experiment:
3. What was chosen as the independent variable?
a. Why was this variable used instead of temperature, or available oxygen?
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3. What technique will be used to lower the pH?
4. What are the experimental groups in this experiment? What is the control group?
5. What are constants used in the experiment?
6. Why did we repeat the measurements for each Salsa ?
7. Why is it necessary to homogenize the samples before measuring the pH?
8. What are things that were done in this experiment to ensure that the measurements were as accurate
and precise as possible?
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9. Create a table (below) to record the results of this experiment. Be sure to include both the original
measurements and the averages. Then create a graph to illustrate your results.
10. Write a conclusion. Based on the data, which formulation should you choose? Use the data to
support your decision and make sure you DISCUSS the actual data within your conclusion
THINKING QUESTIONS:
11. What further tests should you do to make sure that people will want to buy your salsa more than
once?
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12. Your coworker shows you an abstract (summary) of a study that voices concerns about using a pH of
4.6 as a good “benchmark” for pH. Read the abstract (below). Do you need to worry about the results
of this article? Would you change your conclusion? Before answering this, you may want to look at a
nutrition label for salsa containing corn. Explain your decision.
http://www.ncbi.nlm.nih.gov/pubmed/39257 (this is the abstract for the last question)
Nature. 1979 Oct 4;281(5730):398-9.
Clostridium botulinum can grow and form toxin at pH values lower than 4.6.
Raatjes GJ, Smelt JP.
Abstract
It is generally accepted that in Clostridium botulinum both growth and toxin formation are completely inhibited at pH
values below 4.6. This critical pH value has been confirmed by many investigators using food as substrate.
Some researchers have occasionally reported growth of C. botulinum and toxin formation at pH values below 4.6, In these
cases retesting determined that the growth and toxin formation occurred in lab situations (in agar, not in foods) where the
media (agar in which the bacteria grew) was heterogeneous or where proper calibration of the pH meter was not done
prior to pH testing.
In our own testing, we have observed that growth and toxin formation by C. botulinum can take place in homogeneous
protein- rich substrates (> 3% protein) at pH values lower than 4.6.
Here is the nutritional label for your salsa
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Part III – Neutralization:
http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/crm3s5_5.swf
Work through the animation and answer the questions. This time if might benefit you to go through the animation
once before beginning the questions.
1. What is the purpose of this experiment?
2. How are we going to accomplish the task?
3. Why does the pH increase as base (NaOH) is added to the acid (be specific!!!)
4. What is the equivalence point?(Why do they use the word “equivalence”? (what is equal)
5. How much NaOH had to be added to 60 ml of HCl to neutralize the HCl?
6. At the equivalence point, what solution exists in the beaker?
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7. You are not responsible for this equation or the math, BUT…just for fun: the formula to calculate the concentration
of an unknown substance through titration is the following:
C1V1 = C2V2 in other words, the concentration of substance 1 multiplied by the volume of substance 1 equals the
concentration of substance 2 multiplied by the volume of substance 2. Use this equation to calculate the
concentration of the HCl used in the animation. SHOW YOUR WORK!
Part IV: Buffering:
Go to the following website:
http://www.johnwiley.net.au/highered/interactions/media/Balancing/content/Balancing/ur6a/screen0.swf
1. What is the normal pH of the blood?
a. What happens if the pH is above 7.4?
b. Below 7.4?
2. Why is it so key that pH is maintained (ie homeostasis). What whould happen to all our chemical reactions if it
were not maintained?
3. List three mechanisms that help maintain the pH system.
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