FST 605 - Laboratory 8 & 9
Dates Performed: February 26 & March 5, 2002
Report Due: March 12, 2002
The purpose of this laboratory exercise is to observe the effects of trace minerals on the course of lipid oxidation and to become familiar with different procedures utilized to evaluate the extent of lipid oxidation that has occurred in the samples. We will look at the effect of an antioxidant. We will see how crystal structure can affect the melting temperature of solid fat. The lab will extend into next week. There will be only one report for the two labs.
The instructor will assign each group one of the following samples:
Corn oil
Olive Oil
Safflower Oil
Butter
Lard
Shortening
Place 100 ml or 70 g (for solid samples) in each of 3 beakers. To each beaker add the following:
1. Nothing - control
2. One copper penny
3. 100 mg BHA
Place the samples in the 60º C oven.
Prepare a sample for the oxygen absorption method. Do a peroxide value and a TBA on the abused oil and on your control oil. Next week you will do TBA and PV on all three samples and determine the weight gain of your control and control + BHT samples.
Abused Oil Sample
Your fresh oil samples should not give measurable quantities for either TBA or peroxides. A sample of old oil is available for you to use. You should perform a TBA and peroxide value on this sample. This will allow you to gain experience in performing these assays on samples that have oxidized.
Sample Preparation for Melting
Fill two test tubes about 1/3 full for each of the solid fat samples (butter, lard and shortening). Place one sample of each in a beaker of water at room temperature. Place the other tubes in a boiling water bath. When the samples have melted, transfer the tubes to an ice water bath. After they have completely solidified (5 minutes) transfer the tubes to the room temperature water bath and let stand for 20 minutes.
Methods
Melting.
Place the duplicate tubes for a given fat in a 60º C water bath and observe. Note which tube melts first. Note how much longer it takes for the other sample to be completely melted. If it does not melt completely in the 60º C bath, transfer it to an 80º C bath and observe. Repeat for the other two sets of samples.
Peroxide Values
Weigh 5.00 + 0.05 g sample into a 250 ml Erlenmeyer flask and then add 30-ml acetic acid-chloroform (3:2) solution. Swirl the flask until the sample is dissolved and add 0.5 ml saturated KI solution. Allow the solution to stand with occasional shaking for one minute and then add 30 ml distilled water. Titrate with 0.01 N Na2S203 adding it gradually with constant and vigorous shaking. Continue the titrating until the yellow color has disappeared. Add about 0.5 ml starch indicator solution. Continue the titration, shaking the flask vigorously near the end point to liberate all the iodine from the CHCl4 layer. And the Na2S203 dropwise until the blue color has just disappeared.
Oxygen Absorption
Before you leave the lab remove beakers 1 and 3 from the oven and obtain samples as described (be sure to replace the beakers when you are done). Zero the balance. Weigh 1.0 ± .003 g of each oil into labeled aluminum weighing dishes. Record the total weight of dish and oil. Place the dishes in a 60º C oven. At the next lab, place the dishes in a desiccator for 30 min. to cool and then weigh to the nearest 0.001 g.
Thiobarbituric Acid Values
Weigh 1.0 g oil into a test tube and dissolve the sample in 1 ml of hexane. Add 20 ml of TBA reagent and then screw the cap on to the tube. Back off the cap to prevent pressure build-up during-refluxing. Heat the tubes in a boiling water bath for exactly 30 minutes and then cool with tap water. Remove and discard the top layer. Read the absorbency of the sample at 530 nm.
Aroma
Compare the aromas of your three samples. Note any off flavors. Check the samples of the other groups. Give each sample a rank for intensity of off aromas.
Results
Give a copy of your weight gain, peroxide value and TBA data for your sample to the instructor before you leave the second lab.
Compare the control samples to those with antioxidant and with added copper. Compare the results obtained with different fats to your samples.
Discuss the comparisons of the melting behavior of control fats to those that had been rapidly cooled.
Questions
1. Why was each test performed?
2. What is the limitation of each test?
3. Which test compared best to the odor values for each sample? Was this test the same for each sample?
4. How can you explain the melting data?