Yogurt has been made and consumed for thousands of years, and is
today recommended for effective regulation of the digestive system. Although
milk from a number of animals (sheep, goat and water buffalo) can be used, it’s more popularly produced by using milk from cows. This process also involves the use of bacteria, which thickens the milk, giving it a tangy taste.
Yogurt is produced through a simple process referred to as fermentation.
Here, the lactose in milk is fermented by rod-shaped bacteria to produce lactic
acid. It is this acid that gives yogurt its characteristics.
Observing Yogurt under the Microscope
Microscopic cover slips
Without Using Stain
Place a drop of
distilled water on the microscopic slide
Using a cotton swab/tooth pick, take a small drop of yogurt and
smear it onto the microscopic slide (try having the smear at the central part
of the slide and make a thin smear)
Gently place the microscopic cover slip on the smear (use blotting
paper to remove excess solution on the side of the slide)
Place the slide on
the stage of the microscope starting with lower magnification (40X) and move to
Note** Yogurt bacteria are not bad, and are therefore safe to use.
The staining process will also
require the use of heat and
methylene blue stain
Place a drop of dilute yogurt
solution on the microscopic slide and spread it to form a thin smear
Allow the slide to dry in air
(without using heat) to form a thin film
Quickly pass the slide three
times above the flame (a bunsen burner can be used) to fix the bacteria. The
side with film should be up
Allow the slide to cool to room
Add a drop of methylene blue
stain on the film and allow it to settle for about 2 minutes
Gently rinse excess stain in a
beaker of water
Place a cover slip on the film
and observe under the microscope starting with low magnification
student will be able to see rod-like organisms, which may be in clusters.
a stained slide, students will be able to observe light bluish rod-like
organisms (individual bacillus or in clusters) moreover, the student may
observe organisms that are round in shape (cocci). These may be in clusters,
isolated or in pairs.
staining may appear a little more complicated than the former, it would prove
to be an easy procedure if the steps are followed appropriately. This would
also be an important process, which would allow the student to compare stained and unstained yogurt slides.
With unstained slides, students are more
likely to see and identify the bacteria if they are in clusters rather than
single, individual cells.
On the other hand, in bright-field, closing the condenser iris diaphragm will
also make the bacteria appear darker, allowing for easier identification.
is a fun and interesting experiment that will allow the student to learn more
about yogurt. It is an opportunity to learn the different between stained and
unstained slides as well as the different types of bacteria that are used to
make the yogurt they drink.
yogurt bacteria are safe to handle in the laboratory, safety is still
emphasized given that students will still come in contact with glass slides and
stains. Gloves should therefore be used at all times while avoiding clutter in
the working space.
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