Summary:

In today’s experiment, you will isolate the fat from chips and fries. This type of fat is not inherent in the food itself; rather, it is used either to improve the taste or “mouth feel” of the food, or to process the food, in this case, to deep fry. This type of fat is the easiest to extract from food. In contrast, isolating fat from meat or other fatty food is much more difficult as it is trapped in the cells or attached to the different membranes. You will calculate the percent of fat by weight. To conclude the experiment, you will devise and carry out a procedure to isolate the fat from Oreo cookie filling and to calculate its percent in the cookie. The technique used in this procedure is solvent extraction, the same method used when making coffee. In this experiment, the fat on the surface of the fries or chips can be extracted into a solvent in which the fat is soluble, leaving the defatted chip or fry behind. The solvent we will use is petroleum ether, obtained by distilling petroleum and similar to gasoline. The boiling temperature of petroleum ether is between 30°C and 60°C, significantly lower than water’s boiling point of 100°C. (For reference, 0°C = 32°F, the freezing point of water; 10°C = 50°F; 20°C = 68°F; and 30°C = 86°F—note that the latter two have the “6” and the “8” transposed.)

Learning Goals / Objectives:

1. Fats are present in many foods.
2. Fats are not soluble in water but are soluble in other solvents.
3. Fats can be isolated from foods by dissolving them in an organic solvent.
4. Saturated fats are solid at room temperature and unsaturated fats are more liquidy.

Background

We have two general reactions when we contemplate dietary fat: “yum” and “yuk”. Like it or not, our body’s biochemistry requires that we have fat in our diet and our appetite responds by desiring fat in the foods that we choose.

A diet with no fat is not a healthy diet. On the other side, we have seen abundant evidence that too much fat in the diet can contribute to cardiovascular disease and other health problems. By itself, fat is neither good nor bad; both extremes of fat in the diet are unhealthy.

As is true with so many things in life, finding the right balance is the key to health and happiness. How much fat in the diet is OK? The generally accepted guideline is that no more than 30% of the Calories in a daily diet should come from fat. Be careful when interpreting this number; it does not say that 30% of the food you eat can be comprised of fat. When dealing with components of food, the Calories do not correlate directly with weight! Each gram of fat produces 9 Calories while each gram of protein or carbohydrate generates only 4 Calories. (Note that food Calories begin with an upper case “C” to distinguish them from scientific calories; a scientific calorie is the amount of heat required to raise the temperature of 1 gram of water by 1° Celsius; a food Calorie is 1000 scientific calories, or 1 kilocalorie, the amount of heat required to raise the temperature of 1000 grams of water by 1° Celsius.) Let’s analyze a Whopper. According to Burger King statistics, a Whopper contains 40 grams of fat (17 grams of this is the mayo), 47 grams of carbohydrate, and 29 grams of protein. WEIGHT % BY WEIGHT CALORIES % BY CALORIES FAT 40 grams 34% 40 x 9 = 360 54% Carbohydrate 47 grams 41% 47 x 4 = 188 28% Protein 29 grams 25% 29 x 4 = 116 18% Only about a third of the weight is from fat, but over half the Calories are from fat.

Setup:

Gather all the materials.

Anticipatory Set:

Have students predict and discuss what foods they believe have the most fat and why. Students will then record their predictions on the data sheet provided.

Instructions / Activities:

Record data on the data sheet provided Work in pairs for this experiment; each pair will do two measurements, one on chips and one on fries unless instructed otherwise. Each pair will then jointly isolate the fat and determine the % fat content in an Oreo cookie.

A. Part 1
1. Place a large plastic weighing boat on the electronic balance.
2. Weigh about 14 g (one-half oz.) of chips or fries; record the weight. Transfer to a mortar.
3. Using the pestle, gently grind and pulverize the sample.
4. Flute a 12.5 cm filter paper as demonstrated by the instructor to prepare for filtration.
5. Add about 20 mL of petroleum ether to the mortar. CAUTION! Petroleum ether is highly flammable; avoid all sources of ignition. Minimize breathing the vapor.
6. Grind the sample with petroleum ether for at least a minute to dissolve the fat. If the level of the solvent is not higher than the solid food, add more petroleum ether.
7. Weigh and record an empty 100-mL or 150-mL beaker. Write your initials on the beaker.
8. Filter the petroleum ether through the filter paper in the funnel into the beaker.
9. Add another 20 mL petroleum ether to the mortar, grind again for a minute, and filter.
10. Place the beaker on a hot plate in the hood. Add a boiling stick to aid the boiling. When bubbling stops completely, all the solvent has evaporated; remove the beaker from the hot plate. Discard the boiling stick.
11. Allow the beaker to cool, then weigh it with the fat. Calculate the weight of fat by difference.
12. Calculate the percent of fat in the sample. Compare with the nutrition label. Be careful to read the amount of fat in one serving size; do not interpret the percent of Calories from fat to be the percent of fat by weight; they are different values.
13. If instructed, add your data to the table of class data.
14. Set the beaker in a bowl containing ice water for 3-4 minutes to see if the fat solidifies. The more saturated a fat is, the more likely it is to solidify. Before running the next sample, it is important to clean the glassware that has contacted the fat. For the mortar, discard the contents in the wastebasket, wipe out with a paper towel, and wash using some Big Orange degreasing solution and a brush. Rinse several times with water, then dry with a paper towel. The beaker should be cleaned similarly; wipe out as much of the fat with a paper towel before using Big Orange. Discard the filter paper. If the funnel has fat residue, ask the instructor for the best method to remove it.

B. Part 2
Repeat for a different sample; each team should do one sample of fries and one of chips.

C. Part 3 Devise and carry out a procedure to determine the percent of fat in an Oreo cookie. (Most of the fat is in the filling, but the cookie part has some too.)

Assessment:

Teacher’s discretion.

Wrap-up / Closure:

Students will answer and discuss the questions. Then they will present their findings.

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