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 Raft.net, which contain a simple explanation of what's happening. A more detailed chemical explanation is available at Butter Through the Ages.

Resources:

SEP: Testing for Lipids, Proteins and Carbohydrates
http://seplessons.ucsf.edu/node/362

Protein, Carbohydrate, Lipid Power Point http://teacher.edmonds.wednet.edu/mths/awelman/index.php?section=documents

Virtual Protein, Carbohydrate, Lipid Lab Tests
http://faculty.kirkwood.edu/apeterk/learningobjects/biologylabs.htm

Home Training Tools Food Lab
http://www.hometrainingtools.com/food-chemistry-projects/a/1591/

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.

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.

Growing Bacteria Cultures

The ingredients and the bacterial smear of the window.

We tried a couple of formulas for homemade growth medium in which we could grow bacteria cultures. In real labs, a vegetable product called agar is used to make a gel. The agar is melted and poured into Petri dishes, and then chilled until it solidifies again. To get bacteria samples, a sterile cotton swab is rubbed across a surface. Then the dish is streaked by rubbing the swab in a zigzag pattern across the agar. It is set aside in a warm place and allowed to grow for several days.

The first formula was from The Science of Life by Frank G. Bottone, Jr. It used combined flavored Jello and SlimFast diet drink. Instead of Petri dishes, we used small plastic cups (the kind they put ketchup in at fast food places) covered with clear plastic wrap held on with a rubber band. For the sterile swabs, we took Q-Tips and dipped them in a cup of boiling water. Sadly, this formula grew mold but no bacteria.

Stirring the gelatin.

We had better luck with the second formula. It came from a website called Science in the Real World and was designed by biologist Teresa Thiel of the University of Missouri. It used unflavored gelatin, beef boullion cubes and sugar. We used bacteria from yogurt, a toilet, the stem of our hydroponic tomato plant, the inside of one of our mouths, the inside of our refrigerator, the inside of our fish tank, a window, the inside of one of our navels, some dirt from our back yard, the kitchen counter, a sock, and one of our fingers.

The naval smear and the finger smear at 7 days.

The dirt smear after 2 days and after 7 days. The fuzz on the right is mold.

The plant smear and window smear (see top) at 7 days.

At the end of the week, we're going to dispose of the smears and bleach out the box so that any possible escaped bacteria won't start infecting our house.

Yogurt

This week for Biology, we made yogurt using a bacterial process. The bacteria ferments the yogurt by converting milk sugar to lactic acid. We used store-bought yogurt as starter to introduce the bacteria into the milk. The milk is heated to kill off bad bacteria and to alter the proteins to give it a better consistency.


There isn't much to do for this experiment so the instructions are in the photo captions.
Source: New York Times. You can also read more about the biology of yogurt making here.

The Ingredients: All you need is some yogurt, milk, a closed container, something to keep it warm, and a candy thermometer.

Put 3 1/2 cups of milk in a pan and heat.



The milk's temperature being tested. You want it to go up to 180 degrees.



Then put the pan inside a larger pan filled with cold water. Cool the milk down to 120 degrees.


The yogurt being poured into the container -- a quart-sized travel mug.
You want to mix in about about 2 tablespoons of yogurt to one quart or less milk.


Keep the container warm for about 12 hours. We put ours in an insulated lunch cooler.
When it's done, put it in the refrigerator. Homemade yogurt will keep for one week. Enjoy!

Foraging

Last week's post for GeekDad featured Wildman Steve Brill, the famous New York City expert on edible weeds and plants. Brill gives tours of parks in the metropolitan NY area. Maybe someday we'll catch one. In the meantime, I'm putting his site in the sidebar in the hopes I work up the nerve to try a wild backyard salad...

Brill has a book you can buy, but on his website there's a wonderful section for kids. He also recommends these Wild Cards. I'm ordering a set. They'll come in handy.

In the Wall Street Journal today:

In Attics and Closets, 'Biohackers' Discover Their Inner Frankenstein
Using Mail-Order DNA and Iguana Heaters, Hobbyists Brew New Life Forms; Is It Risky?

(Something to worry about if you're too successful in getting your kids interested in biology!)

See also my post on DIYbio.