1. Food Safety Dr. Wahida H. Alqahtani
Disclaimer
The texts, tables and images contained in this course presentation are not my own, they can be found on:
References supplied
Atlases or
The web sites
FSN 522
Food Safety Dr. Wahida H. Alqahtani

2. Part 10 out of 2 Enzymatic reactions IN FOOD Dr. Wahida H. Alqahtani
Disclaimer
The texts, tables and images contained in this course presentation are not my own, they can be found on:
References supplied
Atlases or
The web sites
FSN 522
Part 10 out of 2 Enzymatic reactions IN FOOD Dr. Wahida H. Alqahtani

3. Instructors : Dr. Wahida H. Alqahtani
Office : Bldg. 9, Room 57T, Tel: ,
Schedule : Wednesday am
Office Hour: Tuesday pm ,Wednesday 12-1 pm and Thursday 10-12pm, if you can’t come on this time you should take an appointment
References :
The handout of the parts :

4. Objectives: To describe What are enzymes.
To explain enzyme Class Characterizations.
To identify examples of enzymatic Reactions.
To Explain the function of enzymes as catalysts in chemical reactions.
To outline Coagulation of Milk by Rennet Addition.
Preparations: You are expected to prepare for each lecture by reading material to be covered before it is to be presented in class.
Examinations: Exams will consist of one-hour exam and final exam.
Grading: one - hour exams will be 30%, assignments will be 14% , Presentation will be 16% and final exam will be 40 % .

6. Enzymatic Reactions

7. introduction

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

9. Enzymes
Food quality can be changed due to the activity of enzymes during storage or processing
Enzymes can also be used as analytical indicators to follow those changes
Enzyme-catalyzed reactions can either enhance or deteriorate food quality
Changes in color, texture, sensory properties

10. Enzymes They do so through enzyme catalysis
Living organisms must be able to carry out chemical reactions which are thermodynamically very unfavorable
Break and/or form covalent bonds
Alter large structures
Effect three dimensional structure changes
Regulate gene expression
They do so through enzyme catalysis

11. Enzymes
A common biological reaction can take place without enzyme catalysis
…but will take 750,000,000 years
With an enzyme….it takes ~22 milliseconds
Even improvement of a factor of 1,000 would be good
Only 750,000 years
Living system would be impossible

12. Enzyme Class Characterizations
Oxidoreductase
Oxidation/reduction reactions
Transferase
Transfer of one molecule to another (i.e. functional groups)
Hydrolase
Catalyze bond breaking using water (ie. protease, lipase)
Lyase
Catalyze the formation of double bonds, often in dehydration reactions, during bond breaking
Isomerase
Catalyze intramolecular rearrangement of molecules
Ligase
Catalyze covalent attachment of two substrate molecules

13. Oxidation vs Oxidized
The removal of an electron is oxidation (redox reactions).
When a food system is oxidized, oxygen is added to an active binding site
For example, the result of lipid oxidation is that the lipid may become oxidized.
In the food industry, we common speak of “oxidizing agents” versus “reducing agents”. Both are used in foods.

14. Oxidation vs Oxidized
Reducing agents are compounds that can donate an electron in the event of an oxidation reaction.
L-ascorbic acid is an excellent reducing agent as are most antioxidants
Oxidizing agents induce the removal of electrons
Benzoyl peroxide is commonly added to “bleached” wheat flour

15. Effect of Enzymes

16. Effect of Enzymes Enzymes are highly specialized class of proteins:
A bag of sugar can be stored for years with very little conversion to CO2 and H2O.
This conversion is basic to life, for energy.
When consumed, it is converted to chemical energy very fast.
Both enzymatic and non-enzymatic reactions.
Enzymes are highly specialized class of proteins:
Specialized to perform specific chemical reactions.
Specialized to work in specific environments.

17. The importance of enzymes
in the food industry

18. 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

19. controls the action of enzymes

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

21. Properties of Enzymes

22. Properties of Enzymes Specificity of enzymes Sensitivity to pH
Sensitivity to temperature
Kinetic properties of enzymes

23. Specificity of enzymes
Absolute – one enzyme acts only on one substrate (example: urease decomposes only urea; arginase splits only arginine)
Relative – one enzyme acts on different substrates which have the same bond type (example: pepsin splits different proteins)
Stereospecificity – some enzymes can catalyze the transformation only substrates which are in certain geometrical configuration, cis- or trans-

24. Sensitivity to pH
Each enzyme has maximum activity at a particular pH (optimum pH)
For most enzymes the optimum pH is ~7 (there are exceptions)

25. Sensitivity to temperature
-Each enzyme has maximum activity at a particular temperature (optimum temperature)
-Enzyme will denature above 45-50oC
-Most enzymes have temperature optimum of 37o

26. Kinetic properties of enzymes
Study of the effect of substrate concentration on the rate of reaction 26

27. Enzymatic Reactions

28. Chemical Reactions in Foods
Enzymatic
Enzymes are proteins that occur in every living system
Enzymes can have beneficial and detrimental effects
Bacterial fermentations in cheese, pickles, yogurt
Adverse color, texture, flavor, and odor
High degree of specificity (Enzyme – Substrate)
Non-enzymatic
Those reactions that do not require enzymes
Addition, redox, condensation, hydrolysis.

29. Enzymatic Reactions sucrose glucose + fructose
Enzymatic reactions can occur from enzymes naturally present in a food
Or as part of food processing, enzymes are added to foods to enable a desired effect
Enzymes speed up chemical reactions (good or bad) and must be controlled by monitoring time and temperature.
Typically we think of enzymes as “breaking apart” lipids, proteins, or carbs; but there are several enzyme categories
sucrose glucose + fructose
sucrase
“invertase”

30. Enzymatic Browning
Fruits such as apples, pears, peaches, apricots, and bananas, and vegetables such as potatoes quickly turn brown when their tissue is exposed to oxygen.
Such oxygen exposure occurs when the food is sliced or bitten into or when it has sustained bruises, cuts or other injury to the peel.
This “browning reaction” is related to the work of an enzyme called phenolase (or polyphenoloxidase), a conjugated enzyme in which copper is present.

31. Prevention

32. Prevention
- Enzymatic browning can be prevented or slowed in several ways.
- Immersing the “injured” food (for example, apple slices) in cold water slows the browning process.
-The optimum temperature for enzymes to act is 43ºC(109ºF).The lower temperature decreases enzyme activity, and the water limits the enzyme’s access to oxygen.
- Refrigeration slows enzyme activity even more, and boiling temperatures destroy (denature) the enzyme.
- A long-used method for preventing browning involves lowering of pH to by the addition of acids such as ascorbic acid, malic or citric acid

33. Common Enzymatic Reactions

34. Common Enzymatic Reactions
some reactions can also occur without enzymes
HYDROLYSIS
Food molecules split into smaller products, due to the action of enzymes, or other catalysts (heat, acid) in the presence of water
OXIDATION / REDUCTION:
Reactions that cause changes in a food’s chemical structures through the addition or removal of an electron (hydrogen).
Oxidation is the removal of an electron
Reduction is the addition of an electron

35. Common Enzyme Reactions
Carbohydrases : making corn syrup from starch
Proteases : Meat tenderizers
Lipases : Flavor production in chocolate and cheese
Pectinases
Glucose oxidase
Flavor enzymes
Lipoxygenase
Polyphenol oxidase
Rennin (chymosin)

36. Example of Enzymes

37. Enzymes catalyze reactions such as these:

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

39. 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.

40. Coagulation of Sample
Control

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

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

43. The Mechanism
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.

44. Other Example of Enzymes

45. 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.

46. Coenzymes

47. Coenzymes Coenzymes act as group-transfer reagents .
A (CoA, CoASH, or HSCoA) is a coenzyme, notable for its role in the synthesis and oxidation of fatty acids, and the oxidation of pyruvate in the citric acid cycle. All genomes sequenced to date encode enzymes that use coenzyme A as a substrate, and around 4% of cellular enzymes use it (or a thioester, such as acetyl-CoA) as a substrate. In humans, CoA biosynthesis requires cysteine, pantothenate, and adenosine triphosphate (ATP).

48. Coenzyme classification
(1) Metabolite coenzymes - synthesized from common metabolites. (2) Vitamin-derived coenzymes - derivatives of vitamins . Vitamins cannot be synthesized by mammals, but must be obtained as nutrients.

50. Examples of metabolite coenzymes
ATP can donate phosphoryl group
ATP
S-adenosylmethionine
donates methyl groups in many biosynthesis reactions
S-adenosylmethionine 50

51. Vitamin-Derived Coenzymes
Vitamins are required for coenzyme synthesis and must be obtained from nutrients .
Most vitamins must be enzymatically transformed to the coenzyme .
Deficit of vitamin and as result correspondent coenzyme results in the disease .