Food Enzymes: Friend or Foe? A Great Teaching Topic

1. Food Enzymes: Friend or Foe? A Great Teaching Topic Dr. S. Suzanne Nielsen, Purdue University, Dept. Food Science, nielsens@purdue.edu

2. Enzymes in the Food Industry - - Friend or Foe? • What are enzymes? • What controls the action of enzymes? • Why are enzymes important in the food industry? • Examples of enzymes used in the food industry.

3. What are enzymes? • Enzymes are highly specialized proteins that catalyze specific biochemical reactions • Proteins are chains of individual amino acids

4. Enzymes catalyze reactions such as these: Starch  Glucose   -----   Sucrose  Glucose + Fructose  Proteins  Amino Acids 

5. What controls the action of enzymes? • Temperature • Water Content • pH • Chemicals • Alteration of Substrates • Alteration of Products

6. Why are enzymes important in the food industry? • Added or used to cause particular reaction • Advantages • Natural, Nontoxic • Catalyze specific reactions • Active under mild conditions • Active at low concentrations • Can control rate of reaction • Can be inactivated

7. Why are enzymes important in the food industry? • Naturally present – may want to inactivate them • Naturally present – may want them to act • Used as indicators of proper processing • Used to measure another compound in the food

8. Experiments with Food Enzymes • Enzymatic Browning of Fruits and Vegetables • Coagulation of Milk by Rennet Addition

9. Enzymatic Browning of Fruits and Vegetables • Apple (or potato, banana, etc.) slice is put in each of the following solutions. The browning is observed at 5, 10 , and 20 minutes. • Control (no solution; open to air) • Water Only • 0.1% acetic acid • 0.1% citric acid • 0.1% ascorbic acid

10. Samples at 5 minutes Control

11. Samples at 10 minutes Control

12. Samples at 20 minutes Control

13. Control

14. Water

15. 0.1% Acetic Acid

16. 0.1% Citric Acid

17. 0.1% Ascorbic Acid

18. Why? • Ascorbic acid – Acts as antioxidant; Oxygen preferentially oxidized the ascorbate and not the phenolic compounds • Citric acid – Acts as a chelating agent; Complexes copper ions that are necessary for enzyme activity • Acetic acid – a strong organic acid; Reduces the pH below 3.0 and irreversibly inactivates the enzyme • H2O – Oxygen is necessary for the browning reaction; Immersion in H2O restricts the available oxygen

19. Experiments with Food Enzymes • Enzymatic Browning of Fruits and Vegetables • Coagulation of Milk by Rennet Addition

20. Coagulation of Milk by Rennet Addition • Pipette 10 ml of milk into each of 3 test tubes. • To two of the tubes, add ~1.5 ml of a 1% rennet solution. • Mix. (The 3rd tube will serve as a control. It contains no rennet). • Place one of the two tubes with rennet into water at ~37C • Observe the coagulation.

21. Coagulation of Sample • Control

22. Coagulation of Sample • 1% Rennet Solution, No Heat 5 minutes 10 minutes 20 minutes

23. Coagulation of Sample • 1% Rennet Solution, 37C 5 minutes 10 minutes 20 minutes

24. Why? • Rennet • An enzyme obtained from fourth stomach of ruminant animals, and from some microorganisms • Cleaves particular bond in K-casein of milk to initiate milk coagulation • Coagulates milk protein in cheese making • Aids in development of flavor and texture in ripened cheese. • Mild heat speeds up the enzyme reaction.

25. Other Examples of Enzymes in Foods • Milk • Lactase • Alkaline phosphatase • Lipases • Plasmin • Fresh vs. canned pineapple • Bromelain breaks down gelatin in “Jello” • Meat tenderizer – uses bromelain, ficin, or papain • Blanching of vegetables – catalase and peroxidase • Cloudy vs. clear apple juice • Mandarin oranges • Onions – enzyme alliinase acts on sulfur cmpds.

26. Enzymes in the Food Industry - - Friend or Foe? • What are enzymes? • What controls the action of enzymes? • Why are enzymes important in the food industry? • Examples of enzymes used in the food industry.

27. Food Enzymes: Friend or Foe? A Great Teaching Topic Dr. S. Suzanne Nielsen, Purdue University, Dept. Food Science, nielsens@purdue.edu

28. Questions?