Objective

To determine the total lipids in food samples

Background

Many processed foods contain added fats and oils. We call these fats and oils, lipids. Lipids that are solid at room temperature are fats and those that are liquid at room temperature are oils. Lipids provide us with 9 calories of energy per gram. They can be extracted by hydrophobic solvents such as hexane. In this lab we will be using hexane to extract total fats from prepackaged food products.

Materials and Equipment

  1. Prepackaged food products
  2. Mortar and pestle
  3. 150 ml beaker
  4. Hexane
  5. Measuring cylinder
  6. Homogenizer
  7. Filtration apparatus
  8. 140 ml x 140 mm weight boat
  9. Digital scale
  10. Fume hood

Procedure

Note Carefully: In this procedure, you will be working with hexane. Please use gloves and work under the hood. Hexane is a defatting agent and may cause irritation to skin.

  1. Collect the prepackaged food product assigned to your group
  2. Grind approximately 15 grams of the sample using a mortar and pestle
  3. Add 5 grams of the ground sample (in duplicate) to a 150 ml beaker
  4. Measure 50 ml of hexane using a measuring cylinder and pour the hexane in the beaker
  5. Take your beaker to the homogenization station and mix the sample with the hexane for 3 minutes at 10,000 rpm to rapidly extract fat from the sample.
  6. Filter the sample using the filtration apparatus (diagram below). The apparatus consists of a 100 ml filtering flask, a 50 mm Buchner funnel fitted with a 42.5 mm Whatman No. 1 filter paper, clamp, and a vacuum hose.
  7. Collect 140 mm x 140 mm weight boats (one for each replication)
  8. Weigh the weight boat and record the weight
  9. Transfer the extracted lipid solution to the weight boat and leave it in the fume hood until the next lab
  10. When you return, weight the weigh boat with the extracted lipid, and minus the weight of the weigh boat to get the weight of the extracted lipid. Use the answer to calculate the mean percentage of lipids that was extracted from the sample

Figure 1. Filtration station

Figure 2. Homogenizer

Lab Questions (15 points)

  1. Hexane is a _______________ (polar or non-polar) solvent (1 point)
  2. Based on your observation of the extracted lipid, was it mostly fat or oil? (1 point)
  3. Based on the nutrition label, what was the serving size of the product you worked with? (1 point)
  4. Based on the nutrition label what was the total weight (grams) of fat in the product? (1 point)
  5. Based on the weight of the fat on the label, what is the total Calories that you will get from fat alone, when you eat one serving of this product? (2 points)
  6. Based on the labeling information what is the calculated percentage of fat in each serving size of the product? (2 points)
  7. Based on your experiment, what was the percentage of fat in the product? (2 points)
  8. Were the values for question 6 and 7 exactly the same? If not, what could have contributed to differences? Discuss. (5 points)
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Courtney Simons
Courtney Simons
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Courtney Simons is a food science professor. He holds a BS degree in food science and a Ph.D. in cereal science from North Dakota State University.