This document discusses the Maillard reaction, also known as non-enzymatic browning, which is responsible for pleasant flavors in foods like bread, coffee, and chocolate. It produces primary products through the condensation of reducing sugars and amino acids, which then undergo additional reactions to form secondary products that contribute flavor. These secondary products include carbonyls, pyrroles, pyrazines, oxazoles, thiazoles, pyridines, and imidazoles. The document outlines the specific chemical reactions that form several classes of these compounds, such as Strecker degradation producing carbonyls and pyrazines. It also discusses the formation of furanones, pyranones, pyrrolines

1. NON-ENZYMATIC
BROWNING
(MAILLARD REACTION)
Prof. Harish Chopra,
Department of Chemistry,
SLIET, Longowal (Pb) INDIA

2. Introduction
Maillard reaction or non-enzymatic browning is
responsible for some of the most pleasant flavours like
in freshly baked bread or a freshly brewed cup of
coffee or piece of chocolate.
The different types of primary and secondary
products are formed via non-enzymatic browning.
The primary products formed are non-volatile
compounds formed from the condensation of
reducing sugars and 𝝰-amino acids followed by
Amadori rearrangement.
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3. Introduction
These primary products undergo
different types of reactions like
retro aldol, strecker degradation,
heterocyclization, condensation
etc to produce secondary
products, which are responsible
for the flavour.
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The main flavour products of Maillard
reactions include:
❏ Carbonyls,
❏ Pyrroles,
❏ Pyrazines,
❏ Oxazoles,
❏ Thiazoles,
❏ Pyridines,
❏ Imidazoles, etc.

4. Formation of Carbonyls
The carbonyl compounds are formed from the reaction of
amino acids with 𝝰-dicarbonyl compounds and the reaction is
called as Strecker degradation.
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5. Formation of Pyrazines
Pyrazines are the most studied group of flavour compounds and
presently more than 100 different types of pyrazines have been identified
in food products. The alkyl pyrazines generally possess roasted nut
like flavour while alkoxy pyrazines show earthy vegetable
flavour. The condensation of amino acids with 𝝰-dicarbonyl compounds
gives 𝝰-aminoketones (Strecker degradation), which condense with
another molecule of 𝝰-aminoketone and than, undergoes oxidation to
give pyrazines.
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6. Formation of Pyrroles
Pyrroles are nitrogen-containing heterocycles distributed abundantly in
foods. 2-Acetyl pyrrole and formyl pyrrole are the two most widely
distributed pyrroles in foods possessing a caramel like and a sweet
corn like flavour respectively. Pyrroles are synthesized in foods from
Strecker degradation followed by cyclization.
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7. Furanone Flavours
The furanones are five membered oxygen
containing heterocyclic compounds responsible for
caramel like, sweet, fruity, butterscotch or
nutty flavour. 4-Hydroxy-2,5-dimethyl -
3(2H) furanone (Furanenol) has ‘burnt pineapple’
odor and is used extensively as a flavour enhancer for
sweet products. Similarly, five carbon analogue of
maltol and furaneol, cyclotene has a characteristic
sweet maple odor. 4-Methoxy-2,5-dimethyl-
3(2H) furanone has an odor similar to sherry
whereas 4-n- butoxy-2,5-dimethyl-
3(2H)furanone has a characteristic jasmine like 7

8. Pyranone Flavours
The pyranones are six membered oxygen containing heterocyclic
compounds responsible for caramel like flavour. Maltol is one of
the first known compounds with caramel flavour though ethyl maltol
has 4-6 times stronger flavour than maltol.
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9. Formation of Furanones & Pyranones
Furanones & Pyranones are formed from 2,4-dicarbonyl compounds formed
via 2,3-enolization in Maillard reaction. These 2,4-dicarbonyl compounds
may either undergo cyclization followed by dehydration to give
pyranones or form the 4,5-dienol, which readily loses the C6-OH to give
a triketone. Enolic form of this triketone gives furanones via cyclization.
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10. Formation of Pyrrolines & Pyrrolidines
The Strecker degradation of
proline with dicarbonyl
compounds produces both
pyrrolines and pyrrolidines.
Condensation of the
aldehyde and the secondary
amine forms an iminium
carboxylate intermediate,
which undergoes de-
carboxylation followed by
hydrolysis to give pyrrolines
and pyrrolidines.
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11. Oxazoles & Oxazolines
Most of the oxazoles and oxazolines have been found
in food systems, which have undergone non-
enzymatic browning. The oxazoles have characteristic
green, floral or vegetable like odor or cocoa odor or bacon
fatty odor.
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12. Formation of Thiazoles
Alkyl thiazoles are responsible for green, roasted, nutty, vegetable or meaty
odor. Thiazoles or thiazolines are formed when the dicarbonyl compounds
reacts with H2S and NH3, which are products of degradation of amino
acids. The thiazoles can also be formed from the reaction of carbonyl compounds
with cysteine followed by cyclization.
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13. Formation of Polysulfides
Polysulfide heterocyclic compounds are generally found in meat
products. The condensation of H2S, aldehydes and NH3 gives rise to
the formation of these products
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References
The contents are taken from:
Food Chemistry
By
Harish Chopra,
P S Panesar

15. Thank You !
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