Believe it or not, your humble kitchen toaster contains some very hot technology. Its heating elements are wires made of nichrome, a special alloy of nickel and chromium that incandesces (glows like a light bulb), yet doesn't burn up when exposed to the air.
Why does toasting turn a slice of white bread brown? The bread isn't burning when it turns brown. Rather, it's undergoing what chemists call a Maillard reaction--sugars and amino acids in the bread reacting at 310 degrees Fahrenheit (F) to "toast" the bread. Heating also dehydrates the bread (removes water), leaving the slice dry and crunchy.
What happens if your toaster doesn't heat to 310 degrees F? Try it!
Lindstrom, Elizabeth E. (Editor). Odyssey: Adventures in Science. 2009: 18 (3); p. 26.
Friday, April 3, 2009
Do Astronauts Eat Sandwiches?
Sure, they do! It's called a "rocket science sandwich!"
But first, a quick question: "Have you ever dropped a few crumbs while making or eating a sandwich?" Well, you can't do that in space because in zero gravity astronauts accidentally could inhale breadcrumbs floating around in their spacecraft and choke. That's why lunch on the Space Shuttle is served on special "space bread," a tortilla-like wafer that snaps instead of crumbles. To create it, NASA's food scientists used nuclear magnetic resonance (NMR), known as "MRI" in medical testing, to study bread at the atomic level.
Lindstrom, Elizabeth E. (Editor). Odyssey: Adventures in Science. 2009: 18 (3); p. 15.
But first, a quick question: "Have you ever dropped a few crumbs while making or eating a sandwich?" Well, you can't do that in space because in zero gravity astronauts accidentally could inhale breadcrumbs floating around in their spacecraft and choke. That's why lunch on the Space Shuttle is served on special "space bread," a tortilla-like wafer that snaps instead of crumbles. To create it, NASA's food scientists used nuclear magnetic resonance (NMR), known as "MRI" in medical testing, to study bread at the atomic level.
Lindstrom, Elizabeth E. (Editor). Odyssey: Adventures in Science. 2009: 18 (3); p. 15.
Thursday, March 26, 2009
How Powerful Are You?
What’s that got to do with food? Well, food is the body’s basic source of energy, its fuel! Physiologists and nutritionists use kilocalories (kcal) to let us know how much energy our food contains. Let’s say your diet intake is 2400 Calories/day. Notice the big “C” in calorie. A food calorie or “Calorie”—the one you read about on packaged food products and in articles about nutrition—is the same as a kcal. So, if you consume 2400 Calories/day, you’re also consuming 2400 kcal/day. Now, one kcal is equivalent to 4184 joules or 4184 J, the SI unit for energy. Power is given in joules per second (J/s) or watts (W). What all this means is that your daily diet represents about 1 x 107 J/day, and since a day has 86,400 seconds, your average power is about 115 W, a little more than a 100 W light bulb.
How powerful are you if you eat four Cinnabons? One Cinnabon contains 2000 Calories.
Cameron, John R., Skofronick, James G., and Grant, Roderick M. Physics of the Body (Second Edition). Madison, Wisconsin: Medical Physics Publishing, 1999.
How powerful are you if you eat four Cinnabons? One Cinnabon contains 2000 Calories.
Cameron, John R., Skofronick, James G., and Grant, Roderick M. Physics of the Body (Second Edition). Madison, Wisconsin: Medical Physics Publishing, 1999.
Tuesday, March 17, 2009
How Long Can I Store This Food In The Freezer?
In the winter time across the country, especially in the Midwest and Northeast, people sprinkle salt on icy sidewalks and roads to help “melt the ice,” essentially lowering the freezing point of the ice-water system. So, instead of the ice freezing at 0°C, it might not freeze until it’s -6°C or colder—a good thing when winter’s temperatures drop below freezing!
Now what about food that’s been salted, particularly prepared food that will be stored frozen? The prepared food won’t freeze until it’s reached a much lower temperature than if it had been unsalted and will thus have a shorter minimum freezer storage life. If there’s lots of salt in the food, it could take very low temperatures to freeze the food, and, again, decrease the food’s freezer storage life.
Now, fat does not freeze as well as protein or carbohydrate and consequently has a shorter freezer storage life than its two companion nutrients. The implication is clear: If you plan to freeze a cut of meat for a long period, you should probably trim off all or most of its excess fat before freezing it.
How about salt pork and bacon? Both are salty and fatty, depressing their freezing points and making their freezing properties “poor.” Consequently, salt pork and bacon have a short freezer storage life.
Consider ice cream. It is foam that is preserved by freezing. It contains solid globules of milk, fat, tiny air pockets, minute ice crystals, and small droplets of liquid water containing dissolved sugars and salts with suspended milk proteins or lots of solutes! The droplets of water solution do not freeze because of their high concentration of solutes (like the salt on icy sidewalks or in food). Can you see why ice cream goes “bad” or “tastes funny” after a short while in the freezer?
If you want to know the science behind this, take a peek in a chemistry reference under colligative properties. Freezing point depression is just a colligative property of solutions; it is characteristic of the solvent and depends on the concentration, not the nature of the solute.
Look in your freezer. Ask yourself the question, “How long has this (food) been in here?” Then, think about what’s in that food.
Dorin, H., Demmin, P., and Gabel, D. Chemistry: The Study of Matter (Fourth Edition). Englewood Cliffs, New Jersey: Prentice Hall, Inc., 1992.
Hillman, Howard. The New Kitchen Science. New York: Houghton Mifflin Company, 2003.
Now what about food that’s been salted, particularly prepared food that will be stored frozen? The prepared food won’t freeze until it’s reached a much lower temperature than if it had been unsalted and will thus have a shorter minimum freezer storage life. If there’s lots of salt in the food, it could take very low temperatures to freeze the food, and, again, decrease the food’s freezer storage life.
Now, fat does not freeze as well as protein or carbohydrate and consequently has a shorter freezer storage life than its two companion nutrients. The implication is clear: If you plan to freeze a cut of meat for a long period, you should probably trim off all or most of its excess fat before freezing it.
How about salt pork and bacon? Both are salty and fatty, depressing their freezing points and making their freezing properties “poor.” Consequently, salt pork and bacon have a short freezer storage life.
Consider ice cream. It is foam that is preserved by freezing. It contains solid globules of milk, fat, tiny air pockets, minute ice crystals, and small droplets of liquid water containing dissolved sugars and salts with suspended milk proteins or lots of solutes! The droplets of water solution do not freeze because of their high concentration of solutes (like the salt on icy sidewalks or in food). Can you see why ice cream goes “bad” or “tastes funny” after a short while in the freezer?
If you want to know the science behind this, take a peek in a chemistry reference under colligative properties. Freezing point depression is just a colligative property of solutions; it is characteristic of the solvent and depends on the concentration, not the nature of the solute.
Look in your freezer. Ask yourself the question, “How long has this (food) been in here?” Then, think about what’s in that food.
Dorin, H., Demmin, P., and Gabel, D. Chemistry: The Study of Matter (Fourth Edition). Englewood Cliffs, New Jersey: Prentice Hall, Inc., 1992.
Hillman, Howard. The New Kitchen Science. New York: Houghton Mifflin Company, 2003.
Thursday, February 26, 2009
Glass or Crystal?
Natural glass can be formed when volcanoes melt minerals, then force them to Earth's surface where they cool rapidly. Crystals, on the other hand, form underground when minerals are dissolved in water and left to grow over much longer periods of time like thousands or millions of years.
The material we commonly call "glass" is made of silicon dioxide (the most abundant mineral in sand) that's heated until it starts to melt, then super-cooled; this "glass" is really many, many molecules of silicon dioxide that have no repeating pattern.
Now, you may recall that the molecules in a solid aren't free to move around. They are usually locked into a repeating pattern. Not so with glass. Glass feels solid because its molecules aren't free to move around. However, the molecules in glass are not locked into a pattern. Instead, glass's molecules are just a wee bit out of line. This means glass is not a crystal.
But what about a common household item that is a crystal? Let's think about sugar. If you look closely, you will see that granulated sugar is made up of tiny crystalline cubes. The sugar molecules in each tiny crystal are arranged in a regular pattern that forms a cube. You can change these crystals by melting them and by dissolving them in water. When you melt sugar and quickly cool it, you make sugar glass. When you dissolve sugar in water and let the crystals reform over time, you make new, larger sugar crystals.
Here are two yummy ways to transform that sugar sitting in your sugar bowl. Try them!
Cook Up A Batch Of Glass
Materials You Will Need:
Two cups of sugar
One cup of water
2/3 cup of light corn syrup
1/4 teaspoon of cream of tartar
Two-quart cooking pot
Candy thermometer
Wooden spoon
11 x 17 inch cookie sheet with raised edges
Aluminum foil
Non-stick cooking spray
Hot mats
Your Procedure:
1. Place the cookie sheet on top of the hot mats. Make sure the cookie sheet lies flat. Line the cookie sheet with aluminum foil and spray it thoroughly with the non-stick cooking spray.
2. Mix the sugar, water, corn syrup, and cream of tartar in the cooking pot over medium heat. Stir until the mixture begins to boil, about 15 minutes.
3. Stop stirring and use the candy thermometer to take the mixture's temperature. It should be between 200 and 220 degrees Fahrenheit (F).
4. Let the mixture continue to boil, checking the temperature every five minutes. When the temperature reachers 200 degree F, turn off the heat. It should take about 30 to 40 minutes of boiling to reach this temperature.
5. Pour the mixture onto the cookie sheet and allow it to cool.
6. The glass should be cool to the touch after one hour. Test the edges to see if the glass is firm. If it is hard, slowly peel it away from the aluminum foil.
The Result:
You have your very own pane of sugar glass.
Your Conclusion:
When heat is applied to sugar, the sugar melts--the sugar crystals are changed. If the hot mixture is cooled quickly, the sugar crystals do not have enough time to reform and instead, form a substance that looks like "glass."
Why do we add the extra ingredients?
Even "real" glass doesn't contain just one ingredient. The water is your sugar glass helps the sugar to dissolve and prevents it from burning in your pot. The corn syrup and cream of tartar are known as interfering agents, because they prevent the sugar from reforming into crystals.
Rocks Good Enough To Eat
Materials You Will Need:
A piece of cotton string about 12 inches long
One pencil
One paper clip
One heat-proof glass jar approximately one-pint size
One-quart cooking pot
One cup of water
Three cups of sugar
Wooden spoon
Your Procedure:
1. Tie one end of the string to the middle of a pencil.
2. Place the pencil across the top of the jar so that the string hangs down into the jar.
3. Cut the string so that it's long enough to hang from the top to the bottom of the glass jar. Tie the paper clip to the hanging end of the string. The paper clip acts as a weight to help hold the string in place. It's "ok" for the paper clip to touch the bottom of the jar. Put the pencil, string, and paper clip aside.
4. Pour the water into the cooking pot and heat it over a medium-high heat until it boils.
5. Very slowly pour the sugar into the boiling water, stirring constantly as it dissolves. Keep adding sugar while stirring the mixture until you notice that no more sugar will dissolve. You may not need all three cups of sugar. Turn the heat off.
6. Carefully pour the mixture into the jar.
7. Rub a pinch of sugar crystals into the string. Then place the string into the jar, making sure that it hangs straight down.
8. Place the jar in a location where it will not be disturbed. Check it every day and notice what forms on the string. It will probably take at least a week for a sizeable amount of rock candy to appear.
The Result:
Large crystals of sugar form on the submerged string.
Your Conclusion:
When sugar is dissolved in water and left alone with a string (or support), sugar crystals reform over time, making new, larger sugar crystals.
Cox, Mary Beth. "I Know What Glass Is, Thank You." Odyssey: Adventures in Science. November/December (2008): 6-8.
Artinian, Zareh M. "Edible Glass and Rocks!?" Odyssey: Adventures in Science. November/December (2008): 31 - 33.
The material we commonly call "glass" is made of silicon dioxide (the most abundant mineral in sand) that's heated until it starts to melt, then super-cooled; this "glass" is really many, many molecules of silicon dioxide that have no repeating pattern.
Now, you may recall that the molecules in a solid aren't free to move around. They are usually locked into a repeating pattern. Not so with glass. Glass feels solid because its molecules aren't free to move around. However, the molecules in glass are not locked into a pattern. Instead, glass's molecules are just a wee bit out of line. This means glass is not a crystal.
But what about a common household item that is a crystal? Let's think about sugar. If you look closely, you will see that granulated sugar is made up of tiny crystalline cubes. The sugar molecules in each tiny crystal are arranged in a regular pattern that forms a cube. You can change these crystals by melting them and by dissolving them in water. When you melt sugar and quickly cool it, you make sugar glass. When you dissolve sugar in water and let the crystals reform over time, you make new, larger sugar crystals.
Here are two yummy ways to transform that sugar sitting in your sugar bowl. Try them!
Cook Up A Batch Of Glass
Materials You Will Need:
Two cups of sugar
One cup of water
2/3 cup of light corn syrup
1/4 teaspoon of cream of tartar
Two-quart cooking pot
Candy thermometer
Wooden spoon
11 x 17 inch cookie sheet with raised edges
Aluminum foil
Non-stick cooking spray
Hot mats
Your Procedure:
1. Place the cookie sheet on top of the hot mats. Make sure the cookie sheet lies flat. Line the cookie sheet with aluminum foil and spray it thoroughly with the non-stick cooking spray.
2. Mix the sugar, water, corn syrup, and cream of tartar in the cooking pot over medium heat. Stir until the mixture begins to boil, about 15 minutes.
3. Stop stirring and use the candy thermometer to take the mixture's temperature. It should be between 200 and 220 degrees Fahrenheit (F).
4. Let the mixture continue to boil, checking the temperature every five minutes. When the temperature reachers 200 degree F, turn off the heat. It should take about 30 to 40 minutes of boiling to reach this temperature.
5. Pour the mixture onto the cookie sheet and allow it to cool.
6. The glass should be cool to the touch after one hour. Test the edges to see if the glass is firm. If it is hard, slowly peel it away from the aluminum foil.
The Result:
You have your very own pane of sugar glass.
Your Conclusion:
When heat is applied to sugar, the sugar melts--the sugar crystals are changed. If the hot mixture is cooled quickly, the sugar crystals do not have enough time to reform and instead, form a substance that looks like "glass."
Why do we add the extra ingredients?
Even "real" glass doesn't contain just one ingredient. The water is your sugar glass helps the sugar to dissolve and prevents it from burning in your pot. The corn syrup and cream of tartar are known as interfering agents, because they prevent the sugar from reforming into crystals.
Rocks Good Enough To Eat
Materials You Will Need:
A piece of cotton string about 12 inches long
One pencil
One paper clip
One heat-proof glass jar approximately one-pint size
One-quart cooking pot
One cup of water
Three cups of sugar
Wooden spoon
Your Procedure:
1. Tie one end of the string to the middle of a pencil.
2. Place the pencil across the top of the jar so that the string hangs down into the jar.
3. Cut the string so that it's long enough to hang from the top to the bottom of the glass jar. Tie the paper clip to the hanging end of the string. The paper clip acts as a weight to help hold the string in place. It's "ok" for the paper clip to touch the bottom of the jar. Put the pencil, string, and paper clip aside.
4. Pour the water into the cooking pot and heat it over a medium-high heat until it boils.
5. Very slowly pour the sugar into the boiling water, stirring constantly as it dissolves. Keep adding sugar while stirring the mixture until you notice that no more sugar will dissolve. You may not need all three cups of sugar. Turn the heat off.
6. Carefully pour the mixture into the jar.
7. Rub a pinch of sugar crystals into the string. Then place the string into the jar, making sure that it hangs straight down.
8. Place the jar in a location where it will not be disturbed. Check it every day and notice what forms on the string. It will probably take at least a week for a sizeable amount of rock candy to appear.
The Result:
Large crystals of sugar form on the submerged string.
Your Conclusion:
When sugar is dissolved in water and left alone with a string (or support), sugar crystals reform over time, making new, larger sugar crystals.
Cox, Mary Beth. "I Know What Glass Is, Thank You." Odyssey: Adventures in Science. November/December (2008): 6-8.
Artinian, Zareh M. "Edible Glass and Rocks!?" Odyssey: Adventures in Science. November/December (2008): 31 - 33.
Wednesday, February 11, 2009
Why Do Apple Slices Brown If Left Out In The Air?
When fruits or vegetables are peeled or cut, enzymes contained in the plant tissue are released. In the presence of oxygen from the air, the enzyme polyphenol oxidase (phenolase) catalyzes one step in the biochemical conversion of plant phenolic compounds to brown pigments known as melanins. This reaction, called enzymatic browning, occurs readily at warm temperatures when the pH is between 5.0 and 7.0.
The presence of iron or copper can increase the rate of reaction. This can be easily observed when fruit is cut with a rusty knife or mixed in a copper bowl.
Bruising or other injury to the plant tissue disrupts the structural arrangement of constituents within the cells and allows the contents to make contact with oxygen. This may lead to browning of uncooked fruit tissue.
Enzymatic browning can be a significant problem, limiting the shelf life of many fruits and vegetables which have had little heat applied during processing. However, enzymatic browning is not always a defect. The browning reaction contributes to the desirable color and flavor of raisins, prunes, coffee, tea, and cocoa.
Several substances have been used in the food industry to prevent browning of fruits and vegetables. They are: sulfites, ascorbic acid (vitamin C), citric acid and acetic acid (vinegar), and fresh water.
Let's monitor the level of enzymatic browning of apple slices with the following experiment.
The presence of iron or copper can increase the rate of reaction. This can be easily observed when fruit is cut with a rusty knife or mixed in a copper bowl.
Bruising or other injury to the plant tissue disrupts the structural arrangement of constituents within the cells and allows the contents to make contact with oxygen. This may lead to browning of uncooked fruit tissue.
Enzymatic browning can be a significant problem, limiting the shelf life of many fruits and vegetables which have had little heat applied during processing. However, enzymatic browning is not always a defect. The browning reaction contributes to the desirable color and flavor of raisins, prunes, coffee, tea, and cocoa.
Several substances have been used in the food industry to prevent browning of fruits and vegetables. They are: sulfites, ascorbic acid (vitamin C), citric acid and acetic acid (vinegar), and fresh water.
Let's monitor the level of enzymatic browning of apple slices with the following experiment.
Which Substance Works Best To Slow Apple Browning?
Materials You Will Need:
Fresh apple slices
Test solutions for dipping: 0.1% ascorbic acid, 0.1% citric acid, 0.1% acetic acid, and 1.0% acetic
acid
Cup of water
Tongs
Paper towels
Your Procedure:
1. Place an untreated apple slice on a paper towel. Label the towel "Control."
2. Using tongs, dip another apple slice into one of the test solutions for 30 seconds, place it on the towel, and label the towel with the name of the solution. Rinse the tongs and repeat the same procedure for the other three solutions.
3. Soak one slice in water for 30 seconds. Place it on a towel and label the towel "Water Soak."
4. Note the time and temperature in your data table. Observe the slices every 10 minutes for one hour and record your observations.
The Result:
Apple slices treated with citric acid and acetic acid brown the least.
Your Conclusion:
Citric acid and acetic acid retard the browning of the apple slices because they lower the pH which decreases the phenolase activity. Citric acid also ties up copper ions and prevents them from participating in the reaction. Ascorbic acid prevents oxygen from reacting with the phenolase. Soaking in water alone temporarily reduces the level of browning by restricting the amount of oxygen in contact with the apple tissue.
So, What Causes Potato Chips To Develop A Stale Taste And Flavor?
Proteins, carbohydrates, and fats are the principal structural components of living cells. Lipids are a class of food chemicals that include fats and oils. They are the most concentrated source of food energy providing nine calories of energy per gram. In our bodies, lipids carry the fat-soluble vitamins, contribute to food flavor, and help us feel full after eating. Fats and oils are available in many forms; fats are solid at room temperature while oils are liquid.
According to the Institute of Food Technologists, fats, like all food components, undergo deteriorative changes which result in undesirable flavors and odors with time. These changes in fats are given the term "rancidity." Rancidity can be of two types, hydrolytic and oxidative. Hydrolytic rancidity is caused by a breakdown of the fat into glycerol and fatty acids. This is the type of rancidity that gives "rancid" butter its bad flavor.
Oxidative rancidity results from oxidation of unsaturated and polyunsaturated fatty acids. The products of these chemical reactions produce undesirable flavors and odors. These flavors sometimes develop in foods such as peanut butter, potato chips, and crackers. Manufacturers are permitted to add antioxidants to some foods to slow down this oxidative deterioration. The antioxidants normally used are butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), tertiary butyl hydroquinone (TBHQ), and propyl gallate. You may see these terms on the labels of some foods. In some cases, the antioxidant is incorporated in the packaging material; the antioxidant slowly diffuses into the packaged food product during storage, thus protecting the snack. Another means of slowing down oxidation is to package the food so that it is protected from light, moisture, and oxygen--three things that accelerate oxidation.
Try this experiment to demonstrate typical off-flavors in fat caused by oxidative rancidity.
Does Light Cause Potato Chips To Become "Stale?"
According to the Institute of Food Technologists, fats, like all food components, undergo deteriorative changes which result in undesirable flavors and odors with time. These changes in fats are given the term "rancidity." Rancidity can be of two types, hydrolytic and oxidative. Hydrolytic rancidity is caused by a breakdown of the fat into glycerol and fatty acids. This is the type of rancidity that gives "rancid" butter its bad flavor.
Oxidative rancidity results from oxidation of unsaturated and polyunsaturated fatty acids. The products of these chemical reactions produce undesirable flavors and odors. These flavors sometimes develop in foods such as peanut butter, potato chips, and crackers. Manufacturers are permitted to add antioxidants to some foods to slow down this oxidative deterioration. The antioxidants normally used are butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), tertiary butyl hydroquinone (TBHQ), and propyl gallate. You may see these terms on the labels of some foods. In some cases, the antioxidant is incorporated in the packaging material; the antioxidant slowly diffuses into the packaged food product during storage, thus protecting the snack. Another means of slowing down oxidation is to package the food so that it is protected from light, moisture, and oxygen--three things that accelerate oxidation.
Try this experiment to demonstrate typical off-flavors in fat caused by oxidative rancidity.
Does Light Cause Potato Chips To Become "Stale?"
Materials You Will Need:
Fresh potato chips
Pint or quart canning jars with lids
Aluminum foil
Your Procedure:
1. Wrap a pint or quart canning jar with aluminum foil. Tape the foil in place so that no light can enter the container.
2. Place fresh potato chips in the foil-wrapped jar and in a similar clear jar without foil.
3. Taste the potato chips and rate their flavor on a 5 point scale, where 1 = extremely dislike the flavor and 5 = extremely like the flavor. Place the lids on the jars. Create a table and enter the data for Day 0.
4. Place the two jars on a window sill where they will be exposed to sunlight. Turn each jar one-quarter turn each day (or every 24 hours).
5. Taste the potato chips from each jar at intervals of 1-2 days for 1-2 weeks, careful to remove and replace the lids quickly. The length of time for this experiment is dependent on the amount of sunlight that the jars are exposed to. Enter the data into the table.
6. Make a graph of your data, noting the flavor of the potato chips stored these two ways versus storage time. The y-axis should be the flavor score and the x-axis the time in days.
The Result:
Fresh potato chips
Pint or quart canning jars with lids
Aluminum foil
Your Procedure:
1. Wrap a pint or quart canning jar with aluminum foil. Tape the foil in place so that no light can enter the container.
2. Place fresh potato chips in the foil-wrapped jar and in a similar clear jar without foil.
3. Taste the potato chips and rate their flavor on a 5 point scale, where 1 = extremely dislike the flavor and 5 = extremely like the flavor. Place the lids on the jars. Create a table and enter the data for Day 0.
4. Place the two jars on a window sill where they will be exposed to sunlight. Turn each jar one-quarter turn each day (or every 24 hours).
5. Taste the potato chips from each jar at intervals of 1-2 days for 1-2 weeks, careful to remove and replace the lids quickly. The length of time for this experiment is dependent on the amount of sunlight that the jars are exposed to. Enter the data into the table.
6. Make a graph of your data, noting the flavor of the potato chips stored these two ways versus storage time. The y-axis should be the flavor score and the x-axis the time in days.
The Result:
The potato chips in the jar wrapped in aluminum foil retain their desirable flavors. The potato chips in the clear jar develop off-flavors" over time.
Your Conclusion:
Potato chips protected from ultraviolet light do not undergo lipid oxidation and retain their desirable flavors, whereas potato chips not protected develop "off-flavors."
So, can you see now why potato chips that you purchase in the store are packaged to exclude light? What's more, the packaging also excludes water vapor and oxygen. Let your students design experiments to test these lipid oxidation factors!
http://members.ift.org/IFT/Education/EduResources/xfs.htm
Your Conclusion:
Potato chips protected from ultraviolet light do not undergo lipid oxidation and retain their desirable flavors, whereas potato chips not protected develop "off-flavors."
So, can you see now why potato chips that you purchase in the store are packaged to exclude light? What's more, the packaging also excludes water vapor and oxygen. Let your students design experiments to test these lipid oxidation factors!
http://members.ift.org/IFT/Education/EduResources/xfs.htm
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