Flavor Precursors

Introduction:

Flavor production is an important attribute of non-enzymatic browning, commonly referred to as the Maillard reaction. The reaction is enhanced during the heating process. Thus, this reaction is responsible for developing the brown color and flavor in baked products such as bread crust. The complexity of food flavor is often approached by testing flavor precursors in a simplified model system. The purpose of this lab is to observe the types of flavors generated from the interaction of various amino acids and sugars as flavor precursors. Comparisons will be made between a simple and a complex system (amino acid and sugar).

Materials:

14 test tubes
caps to tubes or aluminum foil
2 - test tube racks
Hot water bath
Incubator (oven)
Glucose
50 ml beaker
10 ml graduated cylinder
Electronic scale
Scupula
Distilled water
Hot pads or hot padded gloves
Mineral oil
Amino Acids
2- pipettes

Amino Acids needed:
Amino Acid 100 degrees C 150 degrees C Weight (mg)
Valine X X 33
Leucine X X 36
Methionine X   41
Glutamine X X 42
Aspartic X   37
Arginine X X 59
Phenylalanine X X 46
Lysine   X 41
No Amino Acids   X 0

Procedures:

Sample preparation

  1. Pipette 0.5 ml of 10% glucose solution into each test tube.
  2. Label the test tubes with the correct name of the amino acid and the temperature to be tested.
  3. Add the designated amount of amino acids to each labeled test tubes.

100 degree Celsius

  1. Loosely attach the cap or place a small piece of aluminum foil over the top of the test tube.
  2. Boil the test tubes for 1 hour in a water bath.
  3. The solution should be gently shaken to help solubilize any material adhering to the test tube wall. Some will not be soluble.
  4. Remove the caps one at a time, smelling each solution and then replace the cap.

150 degree Celsius

  1. Pour a layer of mineral oil (1 ml) on top of the amino acid / sugar solution.
  2. Cap the test tube lightly or place a small piece of aluminum foil over the top of the test tube.
  3. Place the test tubes in a 150 degree Celsius oven for 10 minutes.
  4. Remove the tubes and allow them to cool thoroughly.
  5. Remove the caps one at a time, smelling each solution and then replace the cap.

Each aroma should be identified with one of the following descriptors:

Violets Popcorn
Potato Rock Candy
Sweet, Chocolate Chocolate
Caramel Rye Bread
Burnt Cheese, objectionable Penetrating, chocolate
Butterscotch  

Results:

List the smells (aroma) of the amino acids in the given chart.

Amino Acid 100 degree C 150 degree C
Valine    
Leucine    
Methionine   ---------
Glutamine    
Aspartic   ---------
Arginine    
Phenylalanine    
Lysine ---------  
No Amino Acids ---------  

References:

Darrow, Edward E. "Student Research Projects in Food Science, Food Technology And Nutrition." Ohio State University. Columbus, Ohio. 1989.

Fennema, Owen R. "Food Chemistry." Marcel Dekker, Inc. New York. 1985.

ADDITIONAL LABS - INDEX | HOME | MANUAL - VOLUME 1