1. Lecture VI Dehydration/Browning Reactions
Caramelization
Maillard Rx
Lecture #6 - CHO Dehydration/Browning Reactions
Will cover mainly
...Caramelization, and
...Maillard Rx

2. Reactions of Carbohydrates VII Dehydration/Degradation
Carbonyl group (only)
Hydroxyl groups
Anomeric hydroxyl group
Both carbonyl & hydroxyl groups
Hydrolysis
Dehydration/degradation

3. Reactions of Carbohydrates VII Dehydration/Degradation
In Strong Acid HO C H
CHO OH 4 3 O
CHO
Furfural 4 3 2
12% HCl
- 3 H2O 2 5 5 1 1
a pentose

4. Reactions of Carbohydrates VII Dehydration/Degradation
In Strong Acid
HMF O
CHO
HOH2C 4 3
12% HCl
- 3 H2O +
a hexose 2 5 6 1 O C
CH2OH O= O
CHO
CH2
OHC +
hydroxyacetylfuran

5. Reactions of Carbohydrates VII Types of Browning Rxs in Foods
Ascorbic acid
Enzymatic
Caramelizaton
Non-enzymatic - Malliard

6. Reactions of Carbohydrates VII Types of Browning Rxs in Foods I
Type of Browning
Ascorbic Acid
Enzymatic
Caramelization
Maillard
Starting Material (Precursors)
Ascorbic Acid
Phenols
Sugars
Amino groups & carbonyls from sugars, oxidized lipids, etc.

7. Reactions of Carbohydrates VII Types of Browning Rxs in Foods II
Type of Browning
Ascorbic Acid (AA)
Enzymatic
Caramelization
Maillard
General Rx types
oxidation of AA and multiple condensations
Enzymatic ox, followed by multiple condensations
Heat induced ox and multiple condensations
Substitution and multiple condensations

8. Reactions of Carbohydrates VII Browning Rxs - Similarities
Starting Materials (or precursors)
Polyhydroxy compounds
Furfural-type intermediates**
Except for enzymatic browning
Colored end-pdts; all polymers
Pathways to polymers
Some similarities
Some distinct differences

9. Reactions of Carbohydrates VII Ascorbic Acid Browning6 C HO O 5 4 3 2 1 C O O C OH O
CHO OH O C OH O2 O C C OH HF HO HO HO C
CH2OH
CH2OH
CH2OH
Polymers AA
L-DHAA
L-DKA
Anaerobic O
*COOH
*HCOH *O
CHO +
CO2
Furfural

10. Reactions of Carbohydrates VII Dehydration/Degradation
Caramelization I
CH2OH O
CH2 OH O
Heat OH OH
- H2O OH OH
1,6-Anhydro-b-D-glucopranose
(Levoglucosan)
D-glucose

11. O 1st Stage 2nd Stage 3rd Stage Polymers
hydroxyacetylfuran
1st Stage O
enediol
3-deoxyosone
2nd Stage
3rd Stage
Polymers
hydroxymethylfurfural
(HMF)
3,4-dideoxyosone
Formation of hydroxymethylfurfural by dehydration of a hexose enediol

12. Reactions of Carbohydrates VII Caramelization
Third Stage of the Rx, Polymerization O CH
HOCH2 OH + O CH
HOCH2 : +
HMF
-H+ O CH
HMF O C
HOCH2 OH CH
OCH2 H
HOH2C O

13. Reactions of Carbohydrates VII Dehydration/Degradation
Caramelization II
Polymeric, colloidal particles
Types of Caramel particles
Strongly negative (pH 2 – 4.5)
Positive (pH 4.2 – 4.8)
Weakly negative (pH 3 – 4)

14. Reactions of Carbohydrates VII Dehydration/Degradation
CH2CH3 OH
Caramelization III 1 3 4 2 6 5 O OH
CH3 C O= O O=
CH3 OH 1 3 4 2 5 1 3 4 2 6 5 O O= HO
CH3
Ethyl maltol 1 3 4 2 5
Isomaltol
Maltol
2H-4-Hydroxy-5-
methylfuran-3-one

15. Reactions of Carbohydrates VII Dehydration/Degradation
Browning Reactions - non-enzymatic
Caramelization
Maillard reaction
General observations I

16. KITCHEN CHEMISTRY Grilled meats. Crusty bread. Dark beer
KITCHEN CHEMISTRY Grilled meats. Crusty bread. Dark beer. The Maillard reaction gives our favorite foods their taste and aroma.

17. Reactions of Carbohydrates VII Dehydration/Degradation
Browning Reactions - non-enzymatic
Caramelization
Maillard reaction
General observations II
Positive vs negative effects
+ bread crust, soy sauce, cake color, flavor development
- browning of evap milk, “skunky” beer flavor, nutritional destruction of aa’s
Controlling the Rx
pH, RH, Trace minerals

18. Reactions of Carbohydrates VII Dehydration/Degradation
Browning Reactions - non-enzymatic
Caramelization
Maillard reaction (Non-enzymic glycation)
General observations III
Positive vs negative effects
Controlling the Rx
Medical consequenses

19. Reactions of Carbohydrates VII Dehydration/Degradation
Browning Reactions - non-enzymatic
Caramelization
Maillard reaction
Requirements for Rx
Amino groups
Reducing sugar
Water
“Nonacidic” environment

20. Reactions of Carbohydrates VII Dehydration/Degradation
Browning Reactions - non-enzymatic
Caramelization
Maillard reaction
Initial Stage of the Rx
Color development (none)
Reactions
Properties

22. Schiff base

23. Reactions of Carbohydrates VII Maillard reaction
Innital Stage Cpds, Schiff Base Formation
RNH 2
-H2O O
R2C
R2CNHR NR
R2C OH +
Schiff base
HCOOH H
R2CNHR
CO2
H:CO2 -
R2CNHR + + +

24. Reactions of Carbohydrates VII Maillard reaction
CH2OH C OH
C(H)(OH) R N H
Initial Stage, Compounds O
CH2OH OH
CH2OH C OH HC O :
+RNH2
D-Glucopyranose NR
CH2OH C OH HC O
CH2OH OH
NHR
-H2O
mild
a glycosylamine
Schiff Base

25. Reactions of Carbohydrates VII Dehydration/Degradation Amadori Rearrangement- R’ C HC NR OH H R’ C HC NR OH -: R’ C HC OH NR :
-H+
Schiff Base : O R’ C HC
NHR - O R’ C
CH2NHR R’ C HC
NHR O-
-H+
+H+
Amadori product

26. Reactions of Carbohydrates VII Maillard reaction
Initial Stage, Compounds 6 O
CH2OH OH HO
NHR O
CH2OH OH HO
+ H2O 6 5 2
+RNH2 4 5 2 1 3 4 3 1 O
CH2OH OH
NHR 6
Heyns rearrangement
a ketose 5 1 4 2 3
a 2-amino aldose

27. Reactions of Carbohydrates VII Maillard reaction
Initial Stage, Reaction Rate(s)
Pentoses > hexoses (aldoses>ketoses) >disaccharides

28. Reactions of Carbohydrates VII Dehydration/Degradation
Browning Reactions - non-enzymatic
Caramelization
Maillard reaction
Intermediate Stage of the Rx
Color development(buff yellow)
Reactions
Properties

29. Reactions of Carbohydrates VII Maillard reaction
Intermediate Stage, Compounds (Path 1) + O C
CHOH
H2CN OH C
CHOH
HCN
HC=N
-OH- C OH
Amadori product CH
-RNH2
1,2-ene-aminol
CHOH
+H2O O
CHO
HOH2C O C CH HC O C
CH2 HC
CHOH
-H2O
HMF
-H2O
-H2O
3-deoxy-hexosone
+amine
+amine
Melanoidin pigments

30. Reactions of Carbohydrates VII Maillard reaction
Intermediate Stage, Compounds (Path 2) O C
CHOH
H2CN C
H2CN
CHOH OH O C
CH2
CHOH OH
-Amine
Amadori product
1-amino ,3-enediol O C
CH3
CHOH OH O C
CH3
Methyl reductones, a-dicarbonyls
Methyl a-dicarbonyl cpd
-H2O
+amine
+Amine
Melanoidin pigments

31. Reactions of Carbohydrates VII Dehydration/Degradation
Browning Reactions - non-enzymatic
Caramelization
Maillard reaction
Final Stages of the Rx
Color development (brown)
Reactions
Properties

32. Reactions of Carbohydrates VII Maillard reaction
Final Stages of the Rx, Aldol Condensation
CH3CHCH2CHO OH H O C
CH3 + H.
CH2CHO a -
aldol b
CH2OH C OH HC H
CHO b a
CH2OH C OH HC O H + a OH -

33. Reactions of Carbohydrates VII Maillard reaction
Final Stages of the Rx, Strecker Degradation O +
H2N
COOH O
NH2 + H
-CO2
2,3-butanedione
L-valine
3-amino-2-butanone
methylpropanal N O
NH2
H2N + + O2
tetramethylpyrazine
3-amino-2-butanone (X2)

34. Reactions of Carbohydrates VII Maillard reaction
Controlling the Rx - I
Inhibiting techniques
Decrease moisture
Labuza, IFT, 1970, p 618, from Crit Reviews, CRC Press, 1991

35. Reactions of Carbohydrates VII Maillard reaction
Controlling the Rx - II
Inhibiting techniques
Decrease moisture
Liquid systems --
Increase dilution
Lower pH and/or temp
Remove heavy metal ions

36. Reactions of Carbohydrates VII Maillard reaction
CH2OH C OH
C(H)(OH) R N H
Initial Stage, Compounds O
CH2OH OH
CH2OH C OH HC O + X
+RNH3
D-Glucopyranose NR
CH2OH C OH HC O
CH2OH OH
NHR
-H2O
mild
a glycosylamine
Schiff Base

37. Reactions of Carbohydrates VII Maillard reaction
Controlling the Rx - III
Inhibiting techniques
Decrease moisture
Liquid systems --
Increase dilution
Lower pH and/or temp
Remove heavy metal ions
Remove one substrate (sugar)
Add sulfur compound(s)

38. Reactions of Carbohydrates VII Maillard reaction
Controlling the Rx O
CHO R
a furan derivative
HSO3- O
CSO3- R OH H
Melanoidin pigments

39. Reactions of Carbohydrates VII Maillard reaction
Controlling the Rx - IV
Importance of control …..
Loss of nutritive value
Adverse contribution to flavor/odor
Potential toxicity

40. Reactions of Carbohydrates VII Maillard reaction

41. Reactions of Carbohydrates VII Maillard reaction
Controlling the Rx - V
Practical applications I
Cooking

43. Reactions of Carbohydrates VII Maillard reaction
Controlling the Rx - VI
Practical applications II
Cooking
For less browning….