Topic : Maillard reaction

Question 1

Early stage : Maillard reaction

What is the main product from early stage of Maillard reaction?

Answer 1

Amadori / Heyn’s products (which then further get converted into deoxyosones)

Question 2

Early stage : Maillard reaction

What types of reducing sugar form Amadori and Heyn’s products respectively?

Answer 2

Amadori products are formed from aldose sugars and Heyn’s products are formed from ketose sugars.

Question 3

Early stage : Maillard reaction

State the general outline of formation 1-deoxyosones from glucose + AA (only state the important intermediates).

Draw it out

Answer 3

Glucose + AA → glycosylamine → Schiff base (C=N) ⇌ Amadori compound ⇌ 2,3-eneaminol → 1-deoxyosone

Draw : refer to notes

Question 4

Early stage : Maillard reaction

State the general outline of formation 1-deoxyosones from fructose + AA (only state the important intermediates).

Draw it out

Answer 4

Glucose + AA → glycosylamine → Schiff base (C=N) ⇌ Amadori compound ⇌ 1,2-eneaminol → 3-deoxyosone

Draw : refer to notes

Question 5

Early stage : Maillard reaction

What does 1-deoxyosone mean? What does the number 1 mean?

Answer 5

1 : there is no -OH group on carbon 1

Question 6

Intermediate stage : Maillard reaction

What are the 3 different pathways intermediates can undergo to form aroma compounds (mainly volatiles ;; non-volatiles) through the Maillard reaction?

Answer 6

1. Cyclisation
2. Fragmentation
3. Strecker degradation

Question 7

Intermediate stage : Maillard reaction

What are some key cyclisation (dehydration) compounds in the Maillard reaction which gives sweet-smelling, caramel-like aromas?

Answer 7

1. Maltol (from 1-deoxyosone;; derived from Amadori → glucose)
2. 5-hydroxylmethylfurfural(5-HMF) (from 3-deoxyosone;; derived from Heyn’s → fructose)

Question 8

Intermediate stage : Maillard reaction

What 2 types of fragmentation reactions can deoxyosones undergo?

Answer 8

1. Dicarbonyl cleavage
2. Retro-aldol condensation (cleavage reaction)

Question 9

Intermediate stage : Maillard reaction

What is dicarbonyl cleavage?

Answer 9

The cleavage of a C-C bond in a dicarbonyl compound (O=C–C=O)

Question 10

Intermediate stage : Maillard reaction

What is retro aldol condensation?

Answer 10

Aldol = aldehyde + enol (derived from isomerisation of ketone)
It is the reverse of aldol condensation, and it involves cleavage of a C-C bond (in a β-hydroxy carbonyl compound) to produce 2 smaller carbonyl compounds, an aldehyde + ketone

Question 11

Intermediate stage : Maillard reaction

What is a sweet smelling volatile that can be formed through dicarbonyl cleavage of 3-deoxyosone?

Answer 11

2-furfural

Question 12

Intermediate stage : Maillard reaction

What is the key intermediate of dicarbonyl cleavage / retro aldol condensation?

Answer 12

Dicarbonyl compound (e.g. diacetyl, pyruvaldehyde)

Question 13

Intermediate stage : Maillard reaction

The other important intermediate stage reaction in Maillard reaction is Strecker degradation, which involves the reaction of ___ and ____ to form ___ and ___

Answer 13

Reaction of amino acid and dicarbonyl
To form Strecker aldehyde and aminoketones

Question 14

Intermediate stage : Maillard reaction

Draw out a chemical reaction for Strecker degradation (how the R groups change etc)

Answer 14

Refer to notes

Question 15

Intermediate stage : Maillard reaction

The most important Strecker degradation reactions involve ___-containing amino acids, ___ and ____. The Strecker degradation of these amino acids are important in generating ___-like process flavours.

Answer 15

Sulfur
Methionine, cysteine
Meat

Question 16

Intermediate stage : Maillard reaction

What important class of compounds does Strecker degradation of methionine produce and what is their characteristic odor? [4] Name the other initial compound formed and its characteristic odour

Answer 16

Organosulfides.
- Methanethiol (CH₃SH) : rotten cabbage ;; which can be oxidised
- Dimethyl sulfide & dimethyl disulfide (CH₃ - S - S - CH₃ ): rotten cabbage, garlic
- Dimethyl trisulfude (CH₃ - S - S - S - CH₃: garlic, meaty

Initial compound formed from Strecker degradation : aldehyde
- Methional : cooked potato

Question 17

Intermediate stage : Maillard reaction

What important intermediates does Strecker degradation of cysteine produce for final stage heterocycle formation? [2]

Answer 17

Nucleophiles
- H₂S
- NH₃

Question 18

Final stage : Cyclisation products from intermediates

What 2 chemical pathways can furanthiols be formed?

Answer 18

1. H₂S + furans (cyclisation products from deoxyosone)
2. Aldehyde + thiols (followed by cyclisation and dehydration) - check but seems like aldol condensation

Question 19

Final stage : Cyclisation products from intermediates

What is the odour characteristic of furanthiols?

Answer 19

Cooked meat, sulfurous

Question 19

Final stage : Cyclisation products from intermediates

Thiazole and thiazoline are heterocyclic compounds with __ membered rings, containing __ and __ atoms within the ring.

Answer 19

5
S,N

Question 20

Final stage : Cyclisation products from intermediates

What are the 2 reactants to form thiazoline / thiazole?

Answer 20

1. α-mercaptoketone (replacing one O atom on dicarbonyl with SH group)
2. Imine (Schiff base, derived from aldehyde)

Question 21

Final stage : Cyclisation products from intermediates

α-mercaptoketone and imine react to form ___ (intermediate), which then undergoes cyclisation to form ____, and can be oxidised to form _____

Answer 21

Thioaminal
Thiazoline
Thiazole

Question 21

Final stage : Cyclisation products from intermediates

Name the thiazoline / thiazole learnt in lecture and their characteristic aromas.

Answer 21

1. 2-acetyl thiazoline : popcorn (corn-like)
2. 2-acetyl thiazole : roasted, popcorn, nut (peanut)

Thiazoline oxidised into thiazole. Thus, when oxidised, thiazole have more roasted aroma

Question 22

Final stage : Cyclisation products from intermediates

Pyrazines are heterocycles containing 2 __ atoms in their 6-membered ring.

Answer 22

N

Question 22

# **Final stage : Cyclisation products from intermediates** Draw out the pyrazine ring

Answer 22

refer to notes - 6 membered ring, 2 N atoms, 3 conjugated double bonds

Question 23

# **Final stage : Cyclisation products from intermediates** What intermediates are pyrazines made from?

Answer 23

Pyrazines are formed from the dimersation of 2 α-aminoketones, which are products of Strecker degradation

Question 24

# **Final stage : Cyclisation products from intermediates** What is the characteristic aroma of pyrazines, in what kind of food?

Answer 24

Roasted, nutty aroma Commonly associated with coffee / chocolate