Monday, June 29, 2009

Food Labs (Biochemistry)

Biological macromolecules like proteins, lipids (fats), and carbohydrates (sugars and starches)
are the building blocks of living cells. They also use them to store energy. This week, for biology, we made food samples, and tested them for fat and starch. Here is how we did it:

Fat Test
For the fat test, we tested samples of milk, butter, peanut butter, olive oil, Nutella, egg whites, an egg yolk, heavy cream, sunflower seeds, sesame seeds and yogurt. We also used water for the control sample. We tested them by taking a big piece of brown paper-bag-type paper, drawing squares for the samples, and spreading a little of each food in its square. We than waited for around 15 minutes for the food samples to dry. Once dry, any sample containing fat left a dark grease stain on the paper.

Starch Test
The starch test was slightly more complicated. For the starch test, we made samples of cooked pasta, bread, crackers, a blue chip, flour, a potato, sugar, corn starch. Again, we used water as a control. For the set-up, we took a small sample of each food, and put it in a small plastic cup. For the testing, we put a few drops of iodine on the sample. If the sample contained starch, the drops turned blue. This is because (from Wikipedia) "Starch forms an unstable complex (blue colored) in low concentrations of Iodine."

The potato after the Iodine was added.
As it's reacting with the starch,
the brown Iodine turns dark blue.

The sugar after the Iodine was added.
As you can see, the Iodine did not change color,
meaning that the sugar contains no starch.

One of the cracker samples we made after the iodine was added.
This sample has water added because we were trying to contrast it
with a cracker sample that we chewed up. The starch in the chewed-up
sample was supposed to convert to sugar via the enzymes in our saliva.
Unfortunately, we were unable to detect any difference
between the chewed-up sample and the regular sample.

A couple of days earlier, we made butter from heavy cream. All we did was put about half a cup of cream and a pinch of salt in a glass jar and shake it for roughly 15 minutes. First the cream became thick like whipped cream, then it separated into "buttermilk" and butter.

We followed these directions from, which contain a simple explanation of what's happening. A more detailed chemical explanation is available at Butter Through the Ages.


SEP: Testing for Lipids, Proteins and Carbohydrates

Protein, Carbohydrate, Lipid Power Point

Virtual Protein, Carbohydrate, Lipid Lab Tests

Home Training Tools Food Lab

Tuesday, June 9, 2009

What's Living in Our Compost Tube?

We haven't observed any change in temperature, but the food scraps in our compost tube are definitely starting to rot. And things are growing: above, looking down the neck of the soda bottle, you can see an onion sprouting up from the pile. We also took a sample of the water which collects in the bottom of the tube and took a look under the microscope. Check out the videos below:

Here you can see some of the microorganisms living in our compost pile at 40X magnification, shot with a small hand-held digital camera. The worm above is called a nematode. Cornell's Department of Crop and Soil Science has a page about compost inhabitants. They also have an online guide called Composting in the Classroom: Scientific Inquiry for High School Students which we haven't checked out yet but will.

Above is a 400X magnification of the kidney-shaped organisms, which are probably protozoa. Here's a page about Microbial Decomposers, with microphotos, from the city of Euless, Texas.

Tuesday, June 2, 2009

Soda Bottle Compost

This week, we did another experiment having to do with bacteria and other microbes: a compost column. The purpose being to show how microbes in the soil break down old plants and turn it into fertilizer. A regular compost pile, like the one by our backyard vegetable garden, is made up of old leaves and grass cuttings. The documentary "Unseen Life on Earth" mentioned a town that was using a compost pile as its trash pile by burying it in microbe-rich soil. It could decompose all the trash in a couple of years and got up to temperatures of about 140 degrees Fahrenheit.

For our compost tube, we took some old soda bottles, cut them up to make the column, put food scraps in it, and left it for a few days to decompose. We changed the directions a little, but here is the link to the original instructions.

· 2 clear, plastic, 2-liter soda bottles, one with a cap

· Nylon netting or pantyhose

· Rubber band

· Push pin

· Metal skewer or nail

· Wide packing or masking tape

· Coffee filter - basket type

· Scissors and/or box cutter

· Soil

· Vegetable and fruit scraps

· Meat thermometer

· Waterproof marking pen

1. Rinse the soda bottles. Cut the first bottle around the middle. Set the bottom half aside.

2. Take the top half of the bottle and cut again where it widens out. DO NOT CUT ALL THE WAY AROUND. Leave a flap that will act as a hinge, so you can open the top. Set aside.

3. Cut the bottom off the second bottle just above the curve. Discard the bottom.

4. Wrap the netting over the mouth of the bottle and fasten it below the neck with the rubber band.

5. Poke a hole in the top of the cap with the skewer or nail. If you heat the skewer over the stove you can melt a hole through the cap. Make it big enough to slip in the meat thermometer.

6. With the push pin, poke holes in the second bottle all around the sides to allow air to flow into the column. Do the same with with the top of the first bottle.

7. Take the second bottle with the netting and set it upside-down inside the bottom of the first bottle. Place a coffee filter inside the upside-down bottle so it covers the opening.

8. Fit the top of the first bottle inside the upside-down bottle so they form a long column. You may need to cut small V-shapes in the edge of the inner bottle so it lies flat. Use clear packing tape inside and out to fasten the two bottles together. You may need to re-open some of the holes with the push pin.

9. Bend back the hinged top of the uppermost bottle. Fill the column with fruit and vegetable scraps. You can add any plant matter, including leaves from houseplants. Sprinkle some soil over the scraps, and shake or poke down so it’s evenly mixed. If it’s dry, add some water.

10. Close the hinged top and fasten with tape. Screw on the cap. Insert the meat thermometer. Mark the height of the material in the column with the pen, and write down the date.

11. Put the compost column in a place where it can be observed for several weeks without smelling up the house. Check it regularly to see if the height or temperature changes and to see what is happening to the plant material inside.