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The Effects of Fluorescent Bulbs on
Photo-oxidation in Milk
Photo-oxidation
Discussion
Photo-oxidation is defined as oxidation under the
influence of radiant energy as light. This
occurs when a certain substance bonds with an
atom of oxygen. In milk, the substance that is
most likely to react with oxygen is riboflavin.
When milk undergoes photo-oxidation, the proteins
in the milk change character as they take on an
extra oxygen atom and they become slightly
acidic. Milk spoils when enough of the
proteins in it have reacted with the oxygen. The
light induces the reaction, acting as a catalyst
to start it (Aurand et al., 1966). This is true
for the majority of visible light, but not for
all invisible wavelengths. As milk spoils, it
becomes more acidic and then becomes measurable
for the purpose of this experiment.
Our hypothesis was correct since the data
suggests that bright white fluorescent light
bulbs cause the highest rate of spoilage. The
soft white bulb had the second highest rate,
while the daylight bulb changed the milk least
over the set amount of time. Daylight and soft
white have around the same intensity, however the
daylight bulb is tinted more yellow whereas the
soft white is much whiter. The results show that
the bright white bulb is much worse to use over
milk, but the other two colors were not as
distinctive and while daylight is better, it is
not to a great extent (Graph 1). However, all
colors of fluorescent bulbs that were tested
spoiled the milk much less than the incandescent
bulb, which hardened the milk in a matter of
hours (Picture 4).
Melanie Parnon
Fluorescent Bulbs
Fluorescent bulbs will continue to grow in
popularity until incandescent bulbs are obsolete.
Instead of creating light by heating a filament,
they excite gases within the tube using
electricity. The excited gas then reacts with
phosphorescent chemicals to create light that
humans are able to see. This uses much less
energy to create the same amount of light (Kuhl,
2007). Although compact fluorescent bulbs do
save a lot of energy, they are also potentially
much more dangerous. Since they work with
mercury, when a bulb breaks, mercury dust is
released, which is extremely hazardous (Maine
Department of Environmental Protection, 2007).
These bulbs are commonly used in grocery store
cases, giving the light access to mass quantities
of milk. The differences in color are created by
sending the light through different locations in
the light spectrum that has been created by
phosphors. While the whole spectrum is created,
only one color is permitted to be released,
namely, the one that corresponds with the bulbs
name (Oikos, 2007).
Testing pH (Picture 2)
Purpose
This investigation is testing small portions of
milk under different colors of compact
fluorescent bulbs and a medium intensity
incandescent bulb using the pH of the milk as an
indicator. Recent studies have shown that
fluorescent bulbs are more efficient than
incandescent bulbs, but they also produce more
ultraviolet radiation (Kuhl, 2007). If four
kinds of milk are placed under three different
colors of fluorescent compact bulbs, then the
milk under the bright white fluorescent bulb will
be the most acidic after 12 hours because the
wavelength of the light that is entering the milk
is smaller and will deteriorate the proteins more
quickly.
Incandescent Milk Dry After 12 Hours (Picture 4)
Causes
Preliminary Data (Table 1)
One reason why we obtained these results could be
the variation in wavelength. According to the
visible light spectrum, white-purple light has a
much shorter wavelength than yellow. Since the
beams are smaller, they are able to permeate the
milk molecules more easily and to a larger
degree. Another reason might be that milk itself
reflects yellow-white light rays, which is why we
see it as that color. The bright purple-white
light would not be reflected, while the creamier
light would be. Thus, more purple-white light
would be able to infiltrate the milk and
deteriorate the proteins inside.
The three skim milk lids from each fluorescent
bulb color were compared to each other and, based
on the darkness of the pH paper, were numbered
one, two, or three (because there were only three
bulb colors). One was the lightest paper with the
lowest pH, three was the darkest paper with the
highest pH. The lids labeled one changed the
most from the starting pH. This was repeated for
each type of milk. Incandescent samples were
omitted due to the fact that the milk was
completely solid, and the pH could not be taken.
Materials
Experiment in process (Picture 3)
-16 PowerAde caps -3 100W compact fluorescent
bulbs (bright white, daylight, soft white) -1
100W incandescent light bulb -Four light
fixtures -50 Color Phast pH strips -4 cardboard
compartments -1 teaspoon -1 pint skim, 1, 2,
whole milk
Extensions
This study could be improved by using four
identical lamp fixtures, so that the current of
electricity and the height from the table would
be exactly the same. Also, more sensitive pH
paper could be used to obtain the exact pH of the
milk, instead of simply comparing the colors. To
extend this experiment, colored saran wrap could
be placed over the milk samples to recreate the
color of the milk container, and see which one
blocks the most light. Other variables that
could be changed are the height of the lamp, the
color of the light bulbs, or the thickness of the
covering over the milk.
Literature Cited
Materials (Picture 1)
Aurand, L.W., Singletun, J.A., Noble, B.W.
(1966). Photo-oxidation Reactions in Milk.
Journal of Dairy Science, 49 (2) 138.
Dexheimer, E. (1993, September). Fighting the
Light Campaign Aims to Sell More Milk Packaged
in Paperboard. Dairy Foods. Kuhl, Jackson.
(2007, November 8). Are Compact Fluorescent Bulbs
Good for the Environment? SciTech. Maine
Department of Environmental Protection (2007).
Fluorescent Light Bulb Information. Maine State
of Maine. Oikos, Green Building Source (1996).
How to Select Compact Fluorescent Lamps. Iris
Communications, Inc.
Methodology
Screw each bulb into a different light fixture
but do not turn them on. Place a cardboard box
around each lamp fixture. Adjust the fixtures so
that the bulb is approximately 25 cm from the
table. This is about how far milk would be from
the light bulb in a refrigerator if it was on the
second shelf. Set four PowerAde lids in each
cardboard compartment. Pour one teaspoon of milk
into each lid, one of each type per compartment.
Turn all four lights on at the same time and wait
12 hours. After 12 hours, turn off the lights
and stick a pH strip into each lid. Wait 10
minutes for them to saturate and record the pHs
in the data table. Repeat nine times.
Last revised 2/12/08